SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

     NAME
          systemd.exec - Execution environment configuration

     SYNOPSIS
          service.service, socket.socket, mount.mount, swap.swap

     DESCRIPTION
          Unit configuration files for services, sockets, mount
          points, and swap devices share a subset of configuration
          options which define the execution environment of spawned
          processes.

          This man page lists the configuration options shared by
          these four unit types. See systemd.unit(5) for the common
          options of all unit configuration files, and
          systemd.service(5), systemd.socket(5), systemd.swap(5), and
          systemd.mount(5) for more information on the specific unit
          configuration files. The execution specific configuration
          options are configured in the [Service], [Socket], [Mount],
          or [Swap] sections, depending on the unit type.

          In addition, options which control resources through Linux
          Control Groups (cgroups) are listed in systemd.resource-
          control(5). Those options complement options listed here.

     IMPLICIT DEPENDENCIES
          A few execution parameters result in additional, automatic
          dependencies to be added:

          +o   Units with WorkingDirectory=, RootDirectory=,
              RootImage=, RuntimeDirectory=, StateDirectory=,
              CacheDirectory=, LogsDirectory= or
              ConfigurationDirectory= set automatically gain
              dependencies of type Requires= and After= on all mount
              units required to access the specified paths. This is
              equivalent to having them listed explicitly in
              RequiresMountsFor=.

          +o   Similarly, units with PrivateTmp= enabled automatically
              get mount unit dependencies for all mounts required to
              access /tmp/ and /var/tmp/. They will also gain an
              automatic After= dependency on systemd-tmpfiles-
              setup.service(8).

          +o   Units whose standard output or error output is connected
              to journal or kmsg (or their combinations with console
              output, see below) automatically acquire dependencies of
              type After= on systemd-journald.socket.

          +o   Units using LogNamespace= will automatically gain

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              ordering and requirement dependencies on the two socket
              units associated with systemd-journald@.service
              instances.

     PATHS
          The following settings may be used to change a service's
          view of the filesystem. Please note that the paths must be
          absolute and must not contain a ".."  path component.

          WorkingDirectory=
              Takes a directory path relative to the service's root
              directory specified by RootDirectory=, or the special
              value "~". Sets the working directory for executed
              processes. If set to "~", the home directory of the user
              specified in User= is used. If not set, defaults to the
              root directory when systemd is running as a system
              instance and the respective user's home directory if run
              as user. If the setting is prefixed with the "-"
              character, a missing working directory is not considered
              fatal. If RootDirectory=/RootImage= is not set, then
              WorkingDirectory= is relative to the root of the system
              running the service manager. Note that setting this
              parameter might result in additional dependencies to be
              added to the unit (see above).

          RootDirectory=
              Takes a directory path relative to the host's root
              directory (i.e. the root of the system running the
              service manager). Sets the root directory for executed
              processes, with the chroot(2) system call. If this is
              used, it must be ensured that the process binary and all
              its auxiliary files are available in the chroot() jail.
              Note that setting this parameter might result in
              additional dependencies to be added to the unit (see
              above).

              The MountAPIVFS= and PrivateUsers= settings are
              particularly useful in conjunction with RootDirectory=.
              For details, see below.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          RootImage=
              Takes a path to a block device node or regular file as
              argument. This call is similar to RootDirectory= however
              mounts a file system hierarchy from a block device node
              or loopback file instead of a directory. The device node
              or file system image file needs to contain a file system
              without a partition table, or a file system within an
              MBR/MS-DOS or GPT partition table with only a single

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              Linux-compatible partition, or a set of file systems
              within a GPT partition table that follows the
              m[blue]Discoverable Partitions Specificationm[][1].

              When DevicePolicy= is set to "closed" or "strict", or
              set to "auto" and DeviceAllow= is set, then this setting
              adds /dev/loop-control with rw mode, "block-loop" and
              "block-blkext" with rwm mode to DeviceAllow=. See
              systemd.resource-control(5) for the details about
              DevicePolicy= or DeviceAllow=. Also, see PrivateDevices=
              below, as it may change the setting of DevicePolicy=.

              Units making use of RootImage= automatically gain an
              After= dependency on systemd-udevd.service.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          RootImageOptions=
              Takes a comma-separated list of mount options that will
              be used on disk images specified by RootImage=.
              Optionally a partition name can be prefixed, followed by
              colon, in case the image has multiple partitions,
              otherwise partition name "root" is implied. Options for
              multiple partitions can be specified in a single line
              with space separators. Assigning an empty string removes
              previous assignments. Duplicated options are ignored.
              For a list of valid mount options, please refer to
              mount(8).

              Valid partition names follow the m[blue]Discoverable
              Partitions Specificationm[][1].

              Table 1. Accepted partition names allbox tab(:); lB.  T{
              Partition Name T} l l l l l l l l l.  T{ root T} T{
              root-secondary T} T{ home T} T{ srv T} T{ esp T} T{
              xbootldr T} T{ tmp T} T{ var T} T{ usr T}

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          RootHash=
              Takes a data integrity (dm-verity) root hash specified
              in hexadecimal, or the path to a file containing a root
              hash in ASCII hexadecimal format. This option enables
              data integrity checks using dm-verity, if the used image
              contains the appropriate integrity data (see above) or
              if RootVerity= is used. The specified hash must match
              the root hash of integrity data, and is usually at least
              256 bits (and hence 64 formatted hexadecimal characters)

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              long (in case of SHA256 for example). If this option is
              not specified, but the image file carries the
              "user.verity.roothash" extended file attribute (see
              xattr(7)), then the root hash is read from it, also as
              formatted hexadecimal characters. If the extended file
              attribute is not found (or is not supported by the
              underlying file system), but a file with the .roothash
              suffix is found next to the image file, bearing other-
              wise the same name (except if the image has the .raw
              suffix, in which case the root hash file must not have
              it in its name), the root hash is read from it and auto-
              matically used, also as formatted hexadecimal charac-
              ters.

              If the disk image contains a separate /usr/ partition it
              may also be Verity protected, in which case the root
              hash may configured via an extended attribute
              "user.verity.usrhash" or a .usrhash file adjacent to the
              disk image. There's currently no option to configure the
              root hash for the /usr/ file system via the unit file
              directly.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          RootHashSignature=
              Takes a PKCS7 signature of the RootHash= option as a
              path to a DER-encoded signature file, or as an ASCII
              base64 string encoding of a DER-encoded signature pre-
              fixed by "base64:". The dm-verity volume will only be
              opened if the signature of the root hash is valid and
              signed by a public key present in the kernel keyring. If
              this option is not specified, but a file with the
              .roothash.p7s suffix is found next to the image file,
              bearing otherwise the same name (except if the image has
              the .raw suffix, in which case the signature file must
              not have it in its name), the signature is read from it
              and automatically used.

              If the disk image contains a separate /usr/ partition it
              may also be Verity protected, in which case the signa-
              ture for the root hash may configured via a .usrhash.p7s
              file adjacent to the disk image. There's currently no
              option to configure the root hash signature for the
              /usr/ via the unit file directly.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          RootVerity=

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              Takes the path to a data integrity (dm-verity) file.
              This option enables data integrity checks using
              dm-verity, if RootImage= is used and a root-hash is
              passed and if the used image itself does not contains
              the integrity data. The integrity data must be matched
              by the root hash. If this option is not specified, but a
              file with the .verity suffix is found next to the image
              file, bearing otherwise the same name (except if the
              image has the .raw suffix, in which case the verity data
              file must not have it in its name), the verity data is
              read from it and automatically used.

              This option is supported only for disk images that con-
              tain a single file system, without an enveloping parti-
              tion table. Images that contain a GPT partition table
              should instead include both root file system and match-
              ing Verity data in the same image, implementing the
              m[blue]Discoverable Partition Specificationm[][1].

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          MountAPIVFS=
              Takes a boolean argument. If on, a private mount names-
              pace for the unit's processes is created and the API
              file systems /proc/, /sys/, and /dev/ are mounted inside
              of it, unless they are already mounted. Note that this
              option has no effect unless used in conjunction with
              RootDirectory=/RootImage= as these three mounts are gen-
              erally mounted in the host anyway, and unless the root
              directory is changed, the private mount namespace will
              be a 1:1 copy of the host's, and include these three
              mounts. Note that the /dev/ file system of the host is
              bind mounted if this option is used without PrivateDe-
              vices=. To run the service with a private, minimal ver-
              sion of /dev/, combine this option with PrivateDevices=.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          ProtectProc=
              Takes one of "noaccess", "invisible", "ptraceable" or
              "default" (which it defaults to). When set, this con-
              trols the "hidepid=" mount option of the "procfs"
              instance for the unit that controls which directories
              with process metainformation (/proc/PID) are visible and
              accessible: when set to "noaccess" the ability to access
              most of other users' process metadata in /proc/ is taken
              away for processes of the service. When set to "invisi-
              ble" processes owned by other users are hidden from

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              /proc/. If "ptraceable" all processes that cannot be
              ptrace()'ed by a process are hidden to it. If "default"
              no restrictions on /proc/ access or visibility are made.
              For further details see m[blue]The /proc Filesys-
              temm[][2]. It is generally recommended to run most sys-
              tem services with this option set to "invisible". This
              option is implemented via file system namespacing, and
              thus cannot be used with services that shall be able to
              install mount points in the host file system hierarchy.
              Note that the root user is unaffected by this option, so
              to be effective it has to be used together with User= or
              DynamicUser=yes, and also without the "CAP_SYS_PTRACE"
              capability, which also allows a process to bypass this
              feature. It cannot be used for services that need to
              access metainformation about other users' processes.
              This option implies MountAPIVFS=.

              If the kernel doesn't support per-mount point hidepid=
              mount options this setting remains without effect, and
              the unit's processes will be able to access and see
              other process as if the option was not used.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          ProcSubset=
              Takes one of "all" (the default) and "pid". If the lat-
              ter all files and directories not directly associated
              with process management and introspection are made
              invisible in the /proc/ file system configured for the
              unit's processes. This controls the "subset=" mount
              option of the "procfs" instance for the unit. For fur-
              ther details see m[blue]The /proc Filesystemm[][2]. Note
              that Linux exposes various kernel APIs via /proc/, which
              are made unavailable with this setting. Since these APIs
              are used frequently this option is useful only in a few,
              specific cases, and is not suitable for most non-trivial
              programs.

              Much like ProtectProc= above, this is implemented via
              file system mount namespacing, and hence the same
              restrictions apply: it is only available to system ser-
              vices, it disables mount propagation to the host mount
              table, and it implies MountAPIVFS=. Also, like Protect-
              Proc= this setting is gracefully disabled if the used
              kernel does not support the "subset=" mount option of
              "procfs".

          BindPaths=, BindReadOnlyPaths=
              Configures unit-specific bind mounts. A bind mount makes
              a particular file or directory available at an

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              additional place in the unit's view of the file system.
              Any bind mounts created with this option are specific to
              the unit, and are not visible in the host's mount table.
              This option expects a whitespace separated list of bind
              mount definitions. Each definition consists of a
              colon-separated triple of source path, destination path
              and option string, where the latter two are optional. If
              only a source path is specified the source and destina-
              tion is taken to be the same. The option string may be
              either "rbind" or "norbind" for configuring a recursive
              or non-recursive bind mount. If the destination path is
              omitted, the option string must be omitted too. Each
              bind mount definition may be prefixed with "-", in which
              case it will be ignored when its source path does not
              exist.

              BindPaths= creates regular writable bind mounts (unless
              the source file system mount is already marked
              read-only), while BindReadOnlyPaths= creates read-only
              bind mounts. These settings may be used more than once,
              each usage appends to the unit's list of bind mounts. If
              the empty string is assigned to either of these two
              options the entire list of bind mounts defined prior to
              this is reset. Note that in this case both read-only and
              regular bind mounts are reset, regardless which of the
              two settings is used.

              This option is particularly useful when
              RootDirectory=/RootImage= is used. In this case the
              source path refers to a path on the host file system,
              while the destination path refers to a path below the
              root directory of the unit.

              Note that the destination directory must exist or sys-
              temd must be able to create it. Thus, it is not possible
              to use those options for mount points nested underneath
              paths specified in InaccessiblePaths=, or under /home/
              and other protected directories if ProtectHome=yes is
              specified.  TemporaryFileSystem= with ":ro" or
              ProtectHome=tmpfs should be used instead.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          MountImages=
              This setting is similar to RootImage= in that it mounts
              a file system hierarchy from a block device node or
              loopback file, but the destination directory can be
              specified as well as mount options. This option expects
              a whitespace separated list of mount definitions. Each
              definition consists of a colon-separated tuple of source

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              path and destination definitions, optionally followed by
              another colon and a list of mount options.

              Mount options may be defined as a single comma-separated
              list of options, in which case they will be implicitly
              applied to the root partition on the image, or a series
              of colon-separated tuples of partition name and mount
              options. Valid partition names and mount options are the
              same as for RootImageOptions= setting described above.

              Each mount definition may be prefixed with "-", in which
              case it will be ignored when its source path does not
              exist. The source argument is a path to a block device
              node or regular file. If source or destination contain a
              ":", it needs to be escaped as "\:". The device node or
              file system image file needs to follow the same rules as
              specified for RootImage=. Any mounts created with this
              option are specific to the unit, and are not visible in
              the host's mount table.

              These settings may be used more than once, each usage
              appends to the unit's list of mount paths. If the empty
              string is assigned, the entire list of mount paths
              defined prior to this is reset.

              Note that the destination directory must exist or sys-
              temd must be able to create it. Thus, it is not possible
              to use those options for mount points nested underneath
              paths specified in InaccessiblePaths=, or under /home/
              and other protected directories if ProtectHome=yes is
              specified.

              When DevicePolicy= is set to "closed" or "strict", or
              set to "auto" and DeviceAllow= is set, then this setting
              adds /dev/loop-control with rw mode, "block-loop" and
              "block-blkext" with rwm mode to DeviceAllow=. See
              systemd.resource-control(5) for the details about Devi-
              cePolicy= or DeviceAllow=. Also, see PrivateDevices=
              below, as it may change the setting of DevicePolicy=.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

     CREDENTIALS
          These options are only available for system services and are
          not supported for services running in per-user instances of
          the service manager.

          User=, Group=
              Set the UNIX user or group that the processes are exe-
              cuted as, respectively. Takes a single user or group

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              name, or a numeric ID as argument. For system services
              (services run by the system service manager, i.e. man-
              aged by PID 1) and for user services of the root user
              (services managed by root's instance of systemd --user),
              the default is "root", but User= may be used to specify
              a different user. For user services of any other user,
              switching user identity is not permitted, hence the only
              valid setting is the same user the user's service man-
              ager is running as. If no group is set, the default
              group of the user is used. This setting does not affect
              commands whose command line is prefixed with "+".

              Note that this enforces only weak restrictions on the
              user/group name syntax, but will generate warnings in
              many cases where user/group names do not adhere to the
              following rules: the specified name should consist only
              of the characters a-z, A-Z, 0-9, "_" and "-", except for
              the first character which must be one of a-z, A-Z and
              "_" (i.e. digits and "-" are not permitted as first
              character). The user/group name must have at least one
              character, and at most 31. These restrictions are made
              in order to avoid ambiguities and to ensure user/group
              names and unit files remain portable among Linux sys-
              tems. For further details on the names accepted and the
              names warned about see m[blue]User/Group Name Syn-
              taxm[][3].

              When used in conjunction with DynamicUser= the
              user/group name specified is dynamically allocated at
              the time the service is started, and released at the
              time the service is stopped - unless it is already allo-
              cated statically (see below). If DynamicUser= is not
              used the specified user and group must have been created
              statically in the user database no later than the moment
              the service is started, for example using the
              sysusers.d(5) facility, which is applied at boot or
              package install time. If the user does not exist by then
              program invocation will fail.

              If the User= setting is used the supplementary group
              list is initialized from the specified user's default
              group list, as defined in the system's user and group
              database. Additional groups may be configured through
              the SupplementaryGroups= setting (see below).

          DynamicUser=
              Takes a boolean parameter. If set, a UNIX user and group
              pair is allocated dynamically when the unit is started,
              and released as soon as it is stopped. The user and
              group will not be added to /etc/passwd or /etc/group,
              but are managed transiently during runtime. The nss-
              systemd(8) glibc NSS module provides integration of

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              these dynamic users/groups into the system's user and
              group databases. The user and group name to use may be
              configured via User= and Group= (see above). If these
              options are not used and dynamic user/group allocation
              is enabled for a unit, the name of the dynamic
              user/group is implicitly derived from the unit name. If
              the unit name without the type suffix qualifies as valid
              user name it is used directly, otherwise a name incorpo-
              rating a hash of it is used. If a statically allocated
              user or group of the configured name already exists, it
              is used and no dynamic user/group is allocated. Note
              that if User= is specified and the static group with the
              name exists, then it is required that the static user
              with the name already exists. Similarly, if Group= is
              specified and the static user with the name exists, then
              it is required that the static group with the name
              already exists. Dynamic users/groups are allocated from
              the UID/GID range 61184...65519. It is recommended to
              avoid this range for regular system or login users. At
              any point in time each UID/GID from this range is only
              assigned to zero or one dynamically allocated
              users/groups in use. However, UID/GIDs are recycled
              after a unit is terminated. Care should be taken that
              any processes running as part of a unit for which
              dynamic users/groups are enabled do not leave files or
              directories owned by these users/groups around, as a
              different unit might get the same UID/GID assigned later
              on, and thus gain access to these files or directories.
              If DynamicUser= is enabled, RemoveIPC= and PrivateTmp=
              are implied (and cannot be turned off). This ensures
              that the lifetime of IPC objects and temporary files
              created by the executed processes is bound to the run-
              time of the service, and hence the lifetime of the
              dynamic user/group. Since /tmp/ and /var/tmp/ are usu-
              ally the only world-writable directories on a system
              this ensures that a unit making use of dynamic
              user/group allocation cannot leave files around after
              unit termination. Furthermore NoNewPrivileges= and
              RestrictSUIDSGID= are implicitly enabled (and cannot be
              disabled), to ensure that processes invoked cannot take
              benefit or create SUID/SGID files or directories. More-
              over ProtectSystem=strict and ProtectHome=read-only are
              implied, thus prohibiting the service to write to arbi-
              trary file system locations. In order to allow the ser-
              vice to write to certain directories, they have to be
              allow-listed using ReadWritePaths=, but care must be
              taken so that UID/GID recycling doesn't create security
              issues involving files created by the service. Use Run-
              timeDirectory= (see below) in order to assign a writable
              runtime directory to a service, owned by the dynamic
              user/group and removed automatically when the unit is
              terminated. Use StateDirectory=, CacheDirectory= and

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              LogsDirectory= in order to assign a set of writable
              directories for specific purposes to the service in a
              way that they are protected from vulnerabilities due to
              UID reuse (see below). If this option is enabled, care
              should be taken that the unit's processes do not get
              access to directories outside of these explicitly con-
              figured and managed ones. Specifically, do not use Bind-
              Paths= and be careful with AF_UNIX file descriptor pass-
              ing for directory file descriptors, as this would permit
              processes to create files or directories owned by the
              dynamic user/group that are not subject to the lifecycle
              and access guarantees of the service. Defaults to off.

          SupplementaryGroups=
              Sets the supplementary Unix groups the processes are
              executed as. This takes a space-separated list of group
              names or IDs. This option may be specified more than
              once, in which case all listed groups are set as supple-
              mentary groups. When the empty string is assigned, the
              list of supplementary groups is reset, and all assign-
              ments prior to this one will have no effect. In any way,
              this option does not override, but extends the list of
              supplementary groups configured in the system group
              database for the user. This does not affect commands
              prefixed with "+".

          PAMName=
              Sets the PAM service name to set up a session as. If
              set, the executed process will be registered as a PAM
              session under the specified service name. This is only
              useful in conjunction with the User= setting, and is
              otherwise ignored. If not set, no PAM session will be
              opened for the executed processes. See pam(8) for
              details.

              Note that for each unit making use of this option a PAM
              session handler process will be maintained as part of
              the unit and stays around as long as the unit is active,
              to ensure that appropriate actions can be taken when the
              unit and hence the PAM session terminates. This process
              is named "(sd-pam)" and is an immediate child process of
              the unit's main process.

              Note that when this option is used for a unit it is very
              likely (depending on PAM configuration) that the main
              unit process will be migrated to its own session scope
              unit when it is activated. This process will hence be
              associated with two units: the unit it was originally
              started from (and for which PAMName= was configured),
              and the session scope unit. Any child processes of that
              process will however be associated with the session
              scope unit only. This has implications when used in

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              combination with NotifyAccess=all, as these child pro-
              cesses will not be able to affect changes in the origi-
              nal unit through notification messages. These messages
              will be considered belonging to the session scope unit
              and not the original unit. It is hence not recommended
              to use PAMName= in combination with NotifyAccess=all.

     CAPABILITIES
          These options are only available for system services and are
          not supported for services running in per-user instances of
          the service manager.

          CapabilityBoundingSet=
              Controls which capabilities to include in the capability
              bounding set for the executed process. See capabili-
              ties(7) for details. Takes a whitespace-separated list
              of capability names, e.g.  CAP_SYS_ADMIN,
              CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. Capabilities listed
              will be included in the bounding set, all others are
              removed. If the list of capabilities is prefixed with
              "~", all but the listed capabilities will be included,
              the effect of the assignment inverted. Note that this
              option also affects the respective capabilities in the
              effective, permitted and inheritable capability sets. If
              this option is not used, the capability bounding set is
              not modified on process execution, hence no limits on
              the capabilities of the process are enforced. This
              option may appear more than once, in which case the
              bounding sets are merged by OR, or by AND if the lines
              are prefixed with "~" (see below). If the empty string
              is assigned to this option, the bounding set is reset to
              the empty capability set, and all prior settings have no
              effect. If set to "~" (without any further argument),
              the bounding set is reset to the full set of available
              capabilities, also undoing any previous settings. This
              does not affect commands prefixed with "+".

              Use systemd-analyze(1)'s capability command to retrieve
              a list of capabilities defined on the local system.

              Example: if a unit has the following,

                  CapabilityBoundingSet=CAP_A CAP_B
                  CapabilityBoundingSet=CAP_B CAP_C

              then CAP_A, CAP_B, and CAP_C are set. If the second line
              is prefixed with "~", e.g.,

                  CapabilityBoundingSet=CAP_A CAP_B
                  CapabilityBoundingSet=~CAP_B CAP_C

              then, only CAP_A is set.

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

          AmbientCapabilities=
              Controls which capabilities to include in the ambient
              capability set for the executed process. Takes a
              whitespace-separated list of capability names, e.g.
              CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. This
              option may appear more than once in which case the ambi-
              ent capability sets are merged (see the above examples
              in CapabilityBoundingSet=). If the list of capabilities
              is prefixed with "~", all but the listed capabilities
              will be included, the effect of the assignment inverted.
              If the empty string is assigned to this option, the
              ambient capability set is reset to the empty capability
              set, and all prior settings have no effect. If set to
              "~" (without any further argument), the ambient capabil-
              ity set is reset to the full set of available capabili-
              ties, also undoing any previous settings. Note that
              adding capabilities to ambient capability set adds them
              to the process's inherited capability set.

              Ambient capability sets are useful if you want to exe-
              cute a process as a non-privileged user but still want
              to give it some capabilities. Note that in this case
              option keep-caps is automatically added to SecureBits=
              to retain the capabilities over the user change.  Ambi-
              entCapabilities= does not affect commands prefixed with
              "+".

     SECURITY
          NoNewPrivileges=
              Takes a boolean argument. If true, ensures that the ser-
              vice process and all its children can never gain new
              privileges through execve() (e.g. via setuid or setgid
              bits, or filesystem capabilities). This is the simplest
              and most effective way to ensure that a process and its
              children can never elevate privileges again. Defaults to
              false, but certain settings override this and ignore the
              value of this setting. This is the case when SystemCall-
              Filter=, SystemCallArchitectures=, RestrictAddressFami-
              lies=, RestrictNamespaces=, PrivateDevices=, ProtectKer-
              nelTunables=, ProtectKernelModules=, ProtectKernelLogs=,
              ProtectClock=, MemoryDenyWriteExecute=, RestrictReal-
              time=, RestrictSUIDSGID=, DynamicUser= or LockPersonal-
              ity= are specified. Note that even if this setting is
              overridden by them, systemctl show shows the original
              value of this setting. Also see m[blue]No New Privileges
              Flagm[][4].

          SecureBits=
              Controls the secure bits set for the executed process.
              Takes a space-separated combination of options from the
              following list: keep-caps, keep-caps-locked,
              no-setuid-fixup, no-setuid-fixup-locked, noroot, and

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              noroot-locked. This option may appear more than once, in
              which case the secure bits are ORed. If the empty string
              is assigned to this option, the bits are reset to 0.
              This does not affect commands prefixed with "+". See
              capabilities(7) for details.

     MANDATORY ACCESS CONTROL
          These options are only available for system services and are
          not supported for services running in per-user instances of
          the service manager.

          SELinuxContext=
              Set the SELinux security context of the executed pro-
              cess. If set, this will override the automated domain
              transition. However, the policy still needs to authorize
              the transition. This directive is ignored if SELinux is
              disabled. If prefixed by "-", all errors will be
              ignored. This does not affect commands prefixed with
              "+". See setexeccon(3) for details.

          AppArmorProfile=
              Takes a profile name as argument. The process executed
              by the unit will switch to this profile when started.
              Profiles must already be loaded in the kernel, or the
              unit will fail. If prefixed by "-", all errors will be
              ignored. This setting has no effect if AppArmor is not
              enabled. This setting does not affect commands prefixed
              with "+".

          SmackProcessLabel=
              Takes a SMACK64 security label as argument. The process
              executed by the unit will be started under this label
              and SMACK will decide whether the process is allowed to
              run or not, based on it. The process will continue to
              run under the label specified here unless the executable
              has its own SMACK64EXEC label, in which case the process
              will transition to run under that label. When not speci-
              fied, the label that systemd is running under is used.
              This directive is ignored if SMACK is disabled.

              The value may be prefixed by "-", in which case all
              errors will be ignored. An empty value may be specified
              to unset previous assignments. This does not affect com-
              mands prefixed with "+".

     PROCESS PROPERTIES
          LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=,
          LimitRSS=, LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEM-
          LOCK=, LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=, Limit-
          NICE=, LimitRTPRIO=, LimitRTTIME=
              Set soft and hard limits on various resources for exe-
              cuted processes. See setrlimit(2) for details on the

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              resource limit concept. Resource limits may be specified
              in two formats: either as single value to set a specific
              soft and hard limit to the same value, or as
              colon-separated pair soft:hard to set both limits indi-
              vidually (e.g.  "LimitAS=4G:16G"). Use the string infin-
              ity to configure no limit on a specific resource. The
              multiplicative suffixes K, M, G, T, P and E (to the base
              1024) may be used for resource limits measured in bytes
              (e.g.  "LimitAS=16G"). For the limits referring to time
              values, the usual time units ms, s, min, h and so on may
              be used (see systemd.time(7) for details). Note that if
              no time unit is specified for LimitCPU= the default unit
              of seconds is implied, while for LimitRTTIME= the
              default unit of microseconds is implied. Also, note that
              the effective granularity of the limits might influence
              their enforcement. For example, time limits specified
              for LimitCPU= will be rounded up implicitly to multiples
              of 1s. For LimitNICE= the value may be specified in two
              syntaxes: if prefixed with "+" or "-", the value is
              understood as regular Linux nice value in the range
              -20..19. If not prefixed like this the value is under-
              stood as raw resource limit parameter in the range 0..40
              (with 0 being equivalent to 1).

              Note that most process resource limits configured with
              these options are per-process, and processes may fork in
              order to acquire a new set of resources that are
              accounted independently of the original process, and may
              thus escape limits set. Also note that LimitRSS= is not
              implemented on Linux, and setting it has no effect.
              Often it is advisable to prefer the resource controls
              listed in systemd.resource-control(5) over these
              per-process limits, as they apply to services as a
              whole, may be altered dynamically at runtime, and are
              generally more expressive. For example, MemoryMax= is a
              more powerful (and working) replacement for LimitRSS=.

              Resource limits not configured explicitly for a unit
              default to the value configured in the various Default-
              LimitCPU=, DefaultLimitFSIZE=, ... options available in
              systemd-system.conf(5), and en if not configured there en
              the kernel or per-user defaults, as defined by the OS
              (the latter only for user services, see below).

              For system units these resource limits may be chosen
              freely. When these settings are configured in a user
              service (i.e. a service run by the per-user instance of
              the service manager) they cannot be used to raise the
              limits above those set for the user manager itself when
              it was first invoked, as the user's service manager gen-
              erally lacks the privileges to do so. In user context
              these configuration options are hence only useful to

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              lower the limits passed in or to raise the soft limit to
              the maximum of the hard limit as configured for the
              user. To raise the user's limits further, the available
              configuration mechanisms differ between operating sys-
              tems, but typically require privileges. In most cases it
              is possible to configure higher per-user resource limits
              via PAM or by setting limits on the system service
              encapsulating the user's service manager, i.e. the
              user's instance of user@.service. After making such
              changes, make sure to restart the user's service man-
              ager.

              Table 2. Resource limit directives, their equivalent
              ulimit allbox tab(:); lB lB lB.  T{ Directive T}:T{
              ulimit equivalent T}:T{ Unit T} l l l l l l l l l l l l
              l l l l l l l l l l l l l l l l l l l l l l l l l l l l
              l l l l l l l l.  T{ LimitCPU= T}:T{ ulimit -t T}:T{
              Seconds T} T{ LimitFSIZE= T}:T{ ulimit -f T}:T{ Bytes T}
              T{ LimitDATA= T}:T{ ulimit -d T}:T{ Bytes T} T{ Limit-
              STACK= T}:T{ ulimit -s T}:T{ Bytes T} T{ LimitCORE=
              T}:T{ ulimit -c T}:T{ Bytes T} T{ LimitRSS= T}:T{ ulimit
              -m T}:T{ Bytes T} T{ LimitNOFILE= T}:T{ ulimit -n T}:T{
              Number of File Descriptors T} T{ LimitAS= T}:T{ ulimit
              -v T}:T{ Bytes T} T{ LimitNPROC= T}:T{ ulimit -u T}:T{
              Number of Processes T} T{ LimitMEMLOCK= T}:T{ ulimit -l
              T}:T{ Bytes T} T{ LimitLOCKS= T}:T{ ulimit -x T}:T{ Num-
              ber of Locks T} T{ LimitSIGPENDING= T}:T{ ulimit -i
              T}:T{ Number of Queued Signals T} T{ LimitMSGQUEUE=
              T}:T{ ulimit -q T}:T{ Bytes T} T{ LimitNICE= T}:T{
              ulimit -e T}:T{ Nice Level T} T{ LimitRTPRIO= T}:T{
              ulimit -r T}:T{ Realtime Priority T} T{ LimitRTTIME=
              T}:T{ No equivalent T}:T{ Microseconds T}

          UMask=
              Controls the file mode creation mask. Takes an access
              mode in octal notation. See umask(2) for details.
              Defaults to 0022 for system units. For user units the
              default value is inherited from the per-user service
              manager (whose default is in turn inherited from the
              system service manager, and thus typically also is 0022
              - unless overridden by a PAM module). In order to change
              the per-user mask for all user services, consider set-
              ting the UMask= setting of the user's user@.service sys-
              tem service instance. The per-user umask may also be set
              via the umask field of a user's m[blue]JSON User
              Recordm[][5] (for users managed by systemd-
              homed.service(8) this field may be controlled via home-
              ctl --umask=). It may also be set via a PAM module, such
              as pam_umask(8).

          CoredumpFilter=

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              Controls which types of memory mappings will be saved if
              the process dumps core (using the
              /proc/pid/coredump_filter file). Takes a
              whitespace-separated combination of mapping type names
              or numbers (with the default base 16). Mapping type
              names are private-anonymous, shared-anonymous,
              private-file-backed, shared-file-backed, elf-headers,
              private-huge, shared-huge, private-dax, shared-dax, and
              the special values all (all types) and default (the ker-
              nel default of "private-anonymous shared-anonymous
              elf-headers private-huge"). See core(5) for the meaning
              of the mapping types. When specified multiple times, all
              specified masks are ORed. When not set, or if the empty
              value is assigned, the inherited value is not changed.

              Example 1. Add DAX pages to the dump filter

                  CoredumpFilter=default private-dax shared-dax

          KeyringMode=
              Controls how the kernel session keyring is set up for
              the service (see session-keyring(7) for details on the
              session keyring). Takes one of inherit, private, shared.
              If set to inherit no special keyring setup is done, and
              the kernel's default behaviour is applied. If private is
              used a new session keyring is allocated when a service
              process is invoked, and it is not linked up with any
              user keyring. This is the recommended setting for system
              services, as this ensures that multiple services running
              under the same system user ID (in particular the root
              user) do not share their key material among each other.
              If shared is used a new session keyring is allocated as
              for private, but the user keyring of the user configured
              with User= is linked into it, so that keys assigned to
              the user may be requested by the unit's processes. In
              this modes multiple units running processes under the
              same user ID may share key material. Unless inherit is
              selected the unique invocation ID for the unit (see
              below) is added as a protected key by the name
              "invocation_id" to the newly created session keyring.
              Defaults to private for services of the system service
              manager and to inherit for non-service units and for
              services of the user service manager.

          OOMScoreAdjust=
              Sets the adjustment value for the Linux kernel's
              Out-Of-Memory (OOM) killer score for executed processes.
              Takes an integer between -1000 (to disable OOM killing
              of processes of this unit) and 1000 (to make killing of
              processes of this unit under memory pressure very
              likely). See m[blue]proc.txtm[][6] for details. If not
              specified defaults to the OOM score adjustment level of

     Page 17                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              the service manager itself, which is normally at 0.

              Use the OOMPolicy= setting of service units to configure
              how the service manager shall react to the kernel OOM
              killer terminating a process of the service. See
              systemd.service(5) for details.

          TimerSlackNSec=
              Sets the timer slack in nanoseconds for the executed
              processes. The timer slack controls the accuracy of
              wake-ups triggered by timers. See prctl(2) for more
              information. Note that in contrast to most other time
              span definitions this parameter takes an integer value
              in nano-seconds if no unit is specified. The usual time
              units are understood too.

          Personality=
              Controls which kernel architecture uname(2) shall
              report, when invoked by unit processes. Takes one of the
              architecture identifiers x86, x86-64, ppc, ppc-le,
              ppc64, ppc64-le, s390 or s390x. Which personality archi-
              tectures are supported depends on the system architec-
              ture. Usually the 64bit versions of the various system
              architectures support their immediate 32bit personality
              architecture counterpart, but no others. For example,
              x86-64 systems support the x86-64 and x86 personalities
              but no others. The personality feature is useful when
              running 32-bit services on a 64-bit host system. If not
              specified, the personality is left unmodified and thus
              reflects the personality of the host system's kernel.

          IgnoreSIGPIPE=
              Takes a boolean argument. If true, causes SIGPIPE to be
              ignored in the executed process. Defaults to true
              because SIGPIPE generally is useful only in shell pipe-
              lines.

     SCHEDULING
          Nice=
              Sets the default nice level (scheduling priority) for
              executed processes. Takes an integer between -20 (high-
              est priority) and 19 (lowest priority). See setprior-
              ity(2) for details.

          CPUSchedulingPolicy=
              Sets the CPU scheduling policy for executed processes.
              Takes one of other, batch, idle, fifo or rr. See
              sched_setscheduler(2) for details.

          CPUSchedulingPriority=
              Sets the CPU scheduling priority for executed processes.
              The available priority range depends on the selected CPU

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              scheduling policy (see above). For real-time scheduling
              policies an integer between 1 (lowest priority) and 99
              (highest priority) can be used. See
              sched_setscheduler(2) for details.

          CPUSchedulingResetOnFork=
              Takes a boolean argument. If true, elevated CPU schedul-
              ing priorities and policies will be reset when the exe-
              cuted processes call fork(2), and can hence not leak
              into child processes. See sched_setscheduler(2) for
              details. Defaults to false.

          CPUAffinity=
              Controls the CPU affinity of the executed processes.
              Takes a list of CPU indices or ranges separated by
              either whitespace or commas. Alternatively, takes a spe-
              cial "numa" value in which case systemd automatically
              derives allowed CPU range based on the value of NUMA-
              Mask= option. CPU ranges are specified by the lower and
              upper CPU indices separated by a dash. This option may
              be specified more than once, in which case the specified
              CPU affinity masks are merged. If the empty string is
              assigned, the mask is reset, all assignments prior to
              this will have no effect. See sched_setaffinity(2) for
              details.

          NUMAPolicy=
              Controls the NUMA memory policy of the executed pro-
              cesses. Takes a policy type, one of: default, preferred,
              bind, interleave and local. A list of NUMA nodes that
              should be associated with the policy must be specified
              in NUMAMask=. For more details on each policy please
              see, set_mempolicy(2). For overall overview of NUMA sup-
              port in Linux see, numa(7).

          NUMAMask=
              Controls the NUMA node list which will be applied along-
              side with selected NUMA policy. Takes a list of NUMA
              nodes and has the same syntax as a list of CPUs for
              CPUAffinity= option or special "all" value which will
              include all available NUMA nodes in the mask. Note that
              the list of NUMA nodes is not required for default and
              local policies and for preferred policy we expect a sin-
              gle NUMA node.

          IOSchedulingClass=
              Sets the I/O scheduling class for executed processes.
              Takes an integer between 0 and 3 or one of the strings
              none, realtime, best-effort or idle. If the empty string
              is assigned to this option, all prior assignments to
              both IOSchedulingClass= and IOSchedulingPriority= have
              no effect. See ioprio_set(2) for details.

     Page 19                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

          IOSchedulingPriority=
              Sets the I/O scheduling priority for executed processes.
              Takes an integer between 0 (highest priority) and 7
              (lowest priority). The available priorities depend on
              the selected I/O scheduling class (see above). If the
              empty string is assigned to this option, all prior
              assignments to both IOSchedulingClass= and IOScheduling-
              Priority= have no effect. See ioprio_set(2) for details.

     SANDBOXING
          The following sandboxing options are an effective way to
          limit the exposure of the system towards the unit's pro-
          cesses. It is recommended to turn on as many of these
          options for each unit as is possible without negatively
          affecting the process' ability to operate. Note that many of
          these sandboxing features are gracefully turned off on sys-
          tems where the underlying security mechanism is not avail-
          able. For example, ProtectSystem= has no effect if the ker-
          nel is built without file system namespacing or if the ser-
          vice manager runs in a container manager that makes file
          system namespacing unavailable to its payload. Similar,
          RestrictRealtime= has no effect on systems that lack support
          for SECCOMP system call filtering, or in containers where
          support for this is turned off.

          Also note that some sandboxing functionality is generally
          not available in user services (i.e. services run by the
          per-user service manager). Specifically, the various set-
          tings requiring file system namespacing support (such as
          ProtectSystem=) are not available, as the underlying kernel
          functionality is only accessible to privileged processes.
          However, most namespacing settings, that will not work on
          their own in user services, will work when used in conjunc-
          tion with PrivateUsers=true.

          ProtectSystem=
              Takes a boolean argument or the special values "full" or
              "strict". If true, mounts the /usr/ and the boot loader
              directories (/boot and /efi) read-only for processes
              invoked by this unit. If set to "full", the /etc/ direc-
              tory is mounted read-only, too. If set to "strict" the
              entire file system hierarchy is mounted read-only,
              except for the API file system subtrees /dev/, /proc/
              and /sys/ (protect these directories using PrivateDe-
              vices=, ProtectKernelTunables=, ProtectControlGroups=).
              This setting ensures that any modification of the
              vendor-supplied operating system (and optionally its
              configuration, and local mounts) is prohibited for the
              service. It is recommended to enable this setting for
              all long-running services, unless they are involved with
              system updates or need to modify the operating system in
              other ways. If this option is used, ReadWritePaths= may

     Page 20                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              be used to exclude specific directories from being made
              read-only. This setting is implied if DynamicUser= is
              set. This setting cannot ensure protection in all cases.
              In general it has the same limitations as ReadOnly-
              Paths=, see below. Defaults to off.

          ProtectHome=
              Takes a boolean argument or the special values
              "read-only" or "tmpfs". If true, the directories /home/,
              /root, and /run/user are made inaccessible and empty for
              processes invoked by this unit. If set to "read-only",
              the three directories are made read-only instead. If set
              to "tmpfs", temporary file systems are mounted on the
              three directories in read-only mode. The value "tmpfs"
              is useful to hide home directories not relevant to the
              processes invoked by the unit, while still allowing nec-
              essary directories to be made visible when listed in
              BindPaths= or BindReadOnlyPaths=.

              Setting this to "yes" is mostly equivalent to set the
              three directories in InaccessiblePaths=. Similarly,
              "read-only" is mostly equivalent to ReadOnlyPaths=, and
              "tmpfs" is mostly equivalent to TemporaryFileSystem=
              with ":ro".

              It is recommended to enable this setting for all
              long-running services (in particular network-facing
              ones), to ensure they cannot get access to private user
              data, unless the services actually require access to the
              user's private data. This setting is implied if Dynami-
              cUser= is set. This setting cannot ensure protection in
              all cases. In general it has the same limitations as
              ReadOnlyPaths=, see below.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDi-
          rectory=, ConfigurationDirectory=
              These options take a whitespace-separated list of direc-
              tory names. The specified directory names must be rela-
              tive, and may not include "..". If set, when the unit is
              started, one or more directories by the specified names
              will be created (including their parents) below the
              locations defined in the following table. Also, the cor-
              responding environment variable will be defined with the
              full paths of the directories. If multiple directories
              are set, then in the environment variable the paths are
              concatenated with colon (":").

              Table 3. Automatic directory creation and environment

     Page 21                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              variables allbox tab(:); lB lB lB lB.  T{ Directory
              T}:T{ Below path for system units T}:T{ Below path for
              user units T}:T{ Environment variable set T} l l l l l l
              l l l l l l l l l l l l l l.  T{ RuntimeDirectory= T}:T{
              /run/ T}:T{ $XDG_RUNTIME_DIR T}:T{ $RUNTIME_DIRECTORY T}
              T{ StateDirectory= T}:T{ /var/lib/ T}:T{
              $XDG_CONFIG_HOME T}:T{ $STATE_DIRECTORY T} T{ CacheDi-
              rectory= T}:T{ /var/cache/ T}:T{ $XDG_CACHE_HOME T}:T{
              $CACHE_DIRECTORY T} T{ LogsDirectory= T}:T{ /var/log/
              T}:T{ $XDG_CONFIG_HOME/log/ T}:T{ $LOGS_DIRECTORY T} T{
              ConfigurationDirectory= T}:T{ /etc/ T}:T{
              $XDG_CONFIG_HOME T}:T{ $CONFIGURATION_DIRECTORY T}

              In case of RuntimeDirectory= the innermost subdirecto-
              ries are removed when the unit is stopped. It is possi-
              ble to preserve the specified directories in this case
              if RuntimeDirectoryPreserve= is configured to restart or
              yes (see below). The directories specified with StateDi-
              rectory=, CacheDirectory=, LogsDirectory=, Configura-
              tionDirectory= are not removed when the unit is stopped.

              Except in case of ConfigurationDirectory=, the innermost
              specified directories will be owned by the user and
              group specified in User= and Group=. If the specified
              directories already exist and their owning user or group
              do not match the configured ones, all files and directo-
              ries below the specified directories as well as the
              directories themselves will have their file ownership
              recursively changed to match what is configured. As an
              optimization, if the specified directories are already
              owned by the right user and group, files and directories
              below of them are left as-is, even if they do not match
              what is requested. The innermost specified directories
              will have their access mode adjusted to the what is
              specified in RuntimeDirectoryMode=, StateDirectoryMode=,
              CacheDirectoryMode=, LogsDirectoryMode= and Configura-
              tionDirectoryMode=.

              These options imply BindPaths= for the specified paths.
              When combined with RootDirectory= or RootImage= these
              paths always reside on the host and are mounted from
              there into the unit's file system namespace.

              If DynamicUser= is used in conjunction with StateDirec-
              tory=, the logic for CacheDirectory= and LogsDirectory=
              is slightly altered: the directories are created below
              /var/lib/private, /var/cache/private and
              /var/log/private, respectively, which are host directo-
              ries made inaccessible to unprivileged users, which
              ensures that access to these directories cannot be
              gained through dynamic user ID recycling. Symbolic links
              are created to hide this difference in behaviour. Both

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              from perspective of the host and from inside the unit,
              the relevant directories hence always appear directly
              below /var/lib, /var/cache and /var/log.

              Use RuntimeDirectory= to manage one or more runtime
              directories for the unit and bind their lifetime to the
              daemon runtime. This is particularly useful for unprivi-
              leged daemons that cannot create runtime directories in
              /run/ due to lack of privileges, and to make sure the
              runtime directory is cleaned up automatically after use.
              For runtime directories that require more complex or
              different configuration or lifetime guarantees, please
              consider using tmpfiles.d(5).

              The directories defined by these options are always cre-
              ated under the standard paths used by systemd (/var/,
              /run/, /etc/, ...). If the service needs directories in
              a different location, a different mechanism has to be
              used to create them.

              tmpfiles.d(5) provides functionality that overlaps with
              these options. Using these options is recommended,
              because the lifetime of the directories is tied directly
              to the lifetime of the unit, and it is not necessary to
              ensure that the tmpfiles.d configuration is executed
              before the unit is started.

              To remove any of the directories created by these set-
              tings, use the systemctl clean ...  command on the rele-
              vant units, see systemctl(1) for details.

              Example: if a system service unit has the following,

                  RuntimeDirectory=foo/bar baz

              the service manager creates /run/foo (if it does not
              exist), /run/foo/bar, and /run/baz. The directories
              /run/foo/bar and /run/baz except /run/foo are owned by
              the user and group specified in User= and Group=, and
              removed when the service is stopped.

              Example: if a system service unit has the following,

                  RuntimeDirectory=foo/bar
                  StateDirectory=aaa/bbb ccc

              then the environment variable "RUNTIME_DIRECTORY" is set
              with "/run/foo/bar", and "STATE_DIRECTORY" is set with
              "/var/lib/aaa/bbb:/var/lib/ccc".

          RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectory-
          Mode=, LogsDirectoryMode=, ConfigurationDirectoryMode=

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              Specifies the access mode of the directories specified
              in RuntimeDirectory=, StateDirectory=, CacheDirectory=,
              LogsDirectory=, or ConfigurationDirectory=, respec-
              tively, as an octal number. Defaults to 0755. See "Per-
              missions" in path_resolution(7) for a discussion of the
              meaning of permission bits.

          RuntimeDirectoryPreserve=
              Takes a boolean argument or restart. If set to no (the
              default), the directories specified in RuntimeDirectory=
              are always removed when the service stops. If set to
              restart the directories are preserved when the service
              is both automatically and manually restarted. Here, the
              automatic restart means the operation specified in Res-
              tart=, and manual restart means the one triggered by
              systemctl restart foo.service. If set to yes, then the
              directories are not removed when the service is stopped.
              Note that since the runtime directory /run/ is a mount
              point of "tmpfs", then for system services the directo-
              ries specified in RuntimeDirectory= are removed when the
              system is rebooted.

          TimeoutCleanSec=
              Configures a timeout on the clean-up operation requested
              through systemctl clean ..., see systemctl(1) for
              details. Takes the usual time values and defaults to
              infinity, i.e. by default no timeout is applied. If a
              timeout is configured the clean operation will be
              aborted forcibly when the timeout is reached, poten-
              tially leaving resources on disk.

          ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=
              Sets up a new file system namespace for executed pro-
              cesses. These options may be used to limit access a pro-
              cess has to the file system. Each setting takes a
              space-separated list of paths relative to the host's
              root directory (i.e. the system running the service man-
              ager). Note that if paths contain symlinks, they are
              resolved relative to the root directory set with
              RootDirectory=/RootImage=.

              Paths listed in ReadWritePaths= are accessible from
              within the namespace with the same access modes as from
              outside of it. Paths listed in ReadOnlyPaths= are acces-
              sible for reading only, writing will be refused even if
              the usual file access controls would permit this. Nest
              ReadWritePaths= inside of ReadOnlyPaths= in order to
              provide writable subdirectories within read-only direc-
              tories. Use ReadWritePaths= in order to allow-list spe-
              cific paths for write access if ProtectSystem=strict is
              used.

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              Paths listed in InaccessiblePaths= will be made inacces-
              sible for processes inside the namespace along with
              everything below them in the file system hierarchy. This
              may be more restrictive than desired, because it is not
              possible to nest ReadWritePaths=, ReadOnlyPaths=, Bind-
              Paths=, or BindReadOnlyPaths= inside it. For a more
              flexible option, see TemporaryFileSystem=.

              Non-directory paths may be specified as well. These
              options may be specified more than once, in which case
              all paths listed will have limited access from within
              the namespace. If the empty string is assigned to this
              option, the specific list is reset, and all prior
              assignments have no effect.

              Paths in ReadWritePaths=, ReadOnlyPaths= and Inaccessi-
              blePaths= may be prefixed with "-", in which case they
              will be ignored when they do not exist. If prefixed with
              "+" the paths are taken relative to the root directory
              of the unit, as configured with
              RootDirectory=/RootImage=, instead of relative to the
              root directory of the host (see above). When combining
              "-" and "+" on the same path make sure to specify "-"
              first, and "+" second.

              Note that these settings will disconnect propagation of
              mounts from the unit's processes to the host. This means
              that this setting may not be used for services which
              shall be able to install mount points in the main mount
              namespace. For ReadWritePaths= and ReadOnlyPaths= propa-
              gation in the other direction is not affected, i.e.
              mounts created on the host generally appear in the unit
              processes' namespace, and mounts removed on the host
              also disappear there too. In particular, note that mount
              propagation from host to unit will result in unmodified
              mounts to be created in the unit's namespace, i.e. writ-
              able mounts appearing on the host will be writable in
              the unit's namespace too, even when propagated below a
              path marked with ReadOnlyPaths=! Restricting access with
              these options hence does not extend to submounts of a
              directory that are created later on. This means the
              lock-down offered by that setting is not complete, and
              does not offer full protection.

              Note that the effect of these settings may be undone by
              privileged processes. In order to set up an effective
              sandboxed environment for a unit it is thus recommended
              to combine these settings with either
              CapabilityBoundingSet=~CAP_SYS_ADMIN or
              SystemCallFilter=~@mount.

              These options are only available for system services and

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              are not supported for services running in per-user
              instances of the service manager.

          TemporaryFileSystem=
              Takes a space-separated list of mount points for tempo-
              rary file systems (tmpfs). If set, a new file system
              namespace is set up for executed processes, and a tempo-
              rary file system is mounted on each mount point. This
              option may be specified more than once, in which case
              temporary file systems are mounted on all listed mount
              points. If the empty string is assigned to this option,
              the list is reset, and all prior assignments have no
              effect. Each mount point may optionally be suffixed with
              a colon (":") and mount options such as "size=10%" or
              "ro". By default, each temporary file system is mounted
              with "nodev,strictatime,mode=0755". These can be dis-
              abled by explicitly specifying the corresponding mount
              options, e.g., "dev" or "nostrictatime".

              This is useful to hide files or directories not relevant
              to the processes invoked by the unit, while necessary
              files or directories can be still accessed by combining
              with BindPaths= or BindReadOnlyPaths=:

              Example: if a unit has the following,

                  TemporaryFileSystem=/var:ro
                  BindReadOnlyPaths=/var/lib/systemd

              then the invoked processes by the unit cannot see any
              files or directories under /var/ except for
              /var/lib/systemd or its contents.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          PrivateTmp=
              Takes a boolean argument. If true, sets up a new file
              system namespace for the executed processes and mounts
              private /tmp/ and /var/tmp/ directories inside it that
              are not shared by processes outside of the namespace.
              This is useful to secure access to temporary files of
              the process, but makes sharing between processes via
              /tmp/ or /var/tmp/ impossible. If this is enabled, all
              temporary files created by a service in these directo-
              ries will be removed after the service is stopped.
              Defaults to false. It is possible to run two or more
              units within the same private /tmp/ and /var/tmp/ names-
              pace by using the JoinsNamespaceOf= directive, see
              systemd.unit(5) for details. This setting is implied if
              DynamicUser= is set. For this setting the same

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              restrictions regarding mount propagation and privileges
              apply as for ReadOnlyPaths= and related calls, see
              above. Enabling this setting has the side effect of
              adding Requires= and After= dependencies on all mount
              units necessary to access /tmp/ and /var/tmp/. Moreover
              an implicitly After= ordering on systemd-tmpfiles-
              setup.service(8) is added.

              Note that the implementation of this setting might be
              impossible (for example if mount namespaces are not
              available), and the unit should be written in a way that
              does not solely rely on this setting for security.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          PrivateDevices=
              Takes a boolean argument. If true, sets up a new /dev/
              mount for the executed processes and only adds API
              pseudo devices such as /dev/null, /dev/zero or
              /dev/random (as well as the pseudo TTY subsystem) to it,
              but no physical devices such as /dev/sda, system memory
              /dev/mem, system ports /dev/port and others. This is
              useful to securely turn off physical device access by
              the executed process. Defaults to false. Enabling this
              option will install a system call filter to block
              low-level I/O system calls that are grouped in the
              @raw-io set, will also remove CAP_MKNOD and
              CAP_SYS_RAWIO from the capability bounding set for the
              unit (see above), and set DevicePolicy=closed (see
              systemd.resource-control(5) for details). Note that
              using this setting will disconnect propagation of mounts
              from the service to the host (propagation in the oppo-
              site direction continues to work). This means that this
              setting may not be used for services which shall be able
              to install mount points in the main mount namespace. The
              new /dev/ will be mounted read-only and 'noexec'. The
              latter may break old programs which try to set up exe-
              cutable memory by using mmap(2) of /dev/zero instead of
              using MAP_ANON. For this setting the same restrictions
              regarding mount propagation and privileges apply as for
              ReadOnlyPaths= and related calls, see above. If turned
              on and if running in user mode, or in system mode, but
              without the CAP_SYS_ADMIN capability (e.g. setting
              User=), NoNewPrivileges=yes is implied.

              Note that the implementation of this setting might be
              impossible (for example if mount namespaces are not
              available), and the unit should be written in a way that
              does not solely rely on this setting for security.

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          PrivateNetwork=
              Takes a boolean argument. If true, sets up a new network
              namespace for the executed processes and configures only
              the loopback network device "lo" inside it. No other
              network devices will be available to the executed pro-
              cess. This is useful to turn off network access by the
              executed process. Defaults to false. It is possible to
              run two or more units within the same private network
              namespace by using the JoinsNamespaceOf= directive, see
              systemd.unit(5) for details. Note that this option will
              disconnect all socket families from the host, including
              AF_NETLINK and AF_UNIX. Effectively, for AF_NETLINK this
              means that device configuration events received from
              systemd-udevd.service(8) are not delivered to the unit's
              processes. And for AF_UNIX this has the effect that
              AF_UNIX sockets in the abstract socket namespace of the
              host will become unavailable to the unit's processes
              (however, those located in the file system will continue
              to be accessible).

              Note that the implementation of this setting might be
              impossible (for example if network namespaces are not
              available), and the unit should be written in a way that
              does not solely rely on this setting for security.

              When this option is used on a socket unit any sockets
              bound on behalf of this unit will be bound within a pri-
              vate network namespace. This may be combined with Join-
              sNamespaceOf= to listen on sockets inside of network
              namespaces of other services.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          NetworkNamespacePath=
              Takes an absolute file system path refererring to a
              Linux network namespace pseudo-file (i.e. a file like
              /proc/$PID/ns/net or a bind mount or symlink to one).
              When set the invoked processes are added to the network
              namespace referenced by that path. The path has to point
              to a valid namespace file at the moment the processes
              are forked off. If this option is used PrivateNetwork=
              has no effect. If this option is used together with
              JoinsNamespaceOf= then it only has an effect if this
              unit is started before any of the listed units that have
              PrivateNetwork= or NetworkNamespacePath= configured, as
              otherwise the network namespace of those units is

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              reused.

              When this option is used on a socket unit any sockets
              bound on behalf of this unit will be bound within the
              specified network namespace.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          PrivateUsers=
              Takes a boolean argument. If true, sets up a new user
              namespace for the executed processes and configures a
              minimal user and group mapping, that maps the "root"
              user and group as well as the unit's own user and group
              to themselves and everything else to the "nobody" user
              and group. This is useful to securely detach the user
              and group databases used by the unit from the rest of
              the system, and thus to create an effective sandbox
              environment. All files, directories, processes, IPC
              objects and other resources owned by users/groups not
              equaling "root" or the unit's own will stay visible from
              within the unit but appear owned by the "nobody" user
              and group. If this mode is enabled, all unit processes
              are run without privileges in the host user namespace
              (regardless if the unit's own user/group is "root" or
              not). Specifically this means that the process will have
              zero process capabilities on the host's user namespace,
              but full capabilities within the service's user names-
              pace. Settings such as CapabilityBoundingSet= will
              affect only the latter, and there's no way to acquire
              additional capabilities in the host's user namespace.
              Defaults to off.

              When this setting is set up by a per-user instance of
              the service manager, the mapping of the "root" user and
              group to itself is omitted (unless the user manager is
              root). Additionally, in the per-user instance manager
              case, the user namespace will be set up before most
              other namespaces. This means that combining
              PrivateUsers=true with other namespaces will enable use
              of features not normally supported by the per-user
              instances of the service manager.

              This setting is particularly useful in conjunction with
              RootDirectory=/RootImage=, as the need to synchronize
              the user and group databases in the root directory and
              on the host is reduced, as the only users and groups who
              need to be matched are "root", "nobody" and the unit's
              own user and group.

              Note that the implementation of this setting might be

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              impossible (for example if user namespaces are not
              available), and the unit should be written in a way that
              does not solely rely on this setting for security.

          ProtectHostname=
              Takes a boolean argument. When set, sets up a new UTS
              namespace for the executed processes. In addition,
              changing hostname or domainname is prevented. Defaults
              to off.

              Note that the implementation of this setting might be
              impossible (for example if UTS namespaces are not avail-
              able), and the unit should be written in a way that does
              not solely rely on this setting for security.

              Note that when this option is enabled for a service
              hostname changes no longer propagate from the system
              into the service, it is hence not suitable for services
              that need to take notice of system hostname changes
              dynamically.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          ProtectClock=
              Takes a boolean argument. If set, writes to the hardware
              clock or system clock will be denied. It is recommended
              to turn this on for most services that do not need mod-
              ify the clock. Defaults to off. Enabling this option
              removes CAP_SYS_TIME and CAP_WAKE_ALARM from the capa-
              bility bounding set for this unit, installs a system
              call filter to block calls that can set the clock, and
              DeviceAllow=char-rtc r is implied. This ensures
              /dev/rtc0, /dev/rtc1, etc. are made read-only to the
              service. See systemd.resource-control(5) for the details
              about DeviceAllow=.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          ProtectKernelTunables=
              Takes a boolean argument. If true, kernel variables
              accessible through /proc/sys/, /sys/,
              /proc/sysrq-trigger, /proc/latency_stats, /proc/acpi,
              /proc/timer_stats, /proc/fs and /proc/irq will be made
              read-only to all processes of the unit. Usually, tunable
              kernel variables should be initialized only at
              boot-time, for example with the sysctl.d(5) mechanism.
              Few services need to write to these at runtime; it is
              hence recommended to turn this on for most services. For

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              this setting the same restrictions regarding mount prop-
              agation and privileges apply as for ReadOnlyPaths= and
              related calls, see above. Defaults to off. If turned on
              and if running in user mode, or in system mode, but
              without the CAP_SYS_ADMIN capability (e.g. services for
              which User= is set), NoNewPrivileges=yes is implied.
              Note that this option does not prevent indirect changes
              to kernel tunables effected by IPC calls to other pro-
              cesses. However, InaccessiblePaths= may be used to make
              relevant IPC file system objects inaccessible. If Pro-
              tectKernelTunables= is set, MountAPIVFS=yes is implied.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          ProtectKernelModules=
              Takes a boolean argument. If true, explicit module load-
              ing will be denied. This allows module load and unload
              operations to be turned off on modular kernels. It is
              recommended to turn this on for most services that do
              not need special file systems or extra kernel modules to
              work. Defaults to off. Enabling this option removes
              CAP_SYS_MODULE from the capability bounding set for the
              unit, and installs a system call filter to block module
              system calls, also /usr/lib/modules is made inaccessi-
              ble. For this setting the same restrictions regarding
              mount propagation and privileges apply as for ReadOnly-
              Paths= and related calls, see above. Note that limited
              automatic module loading due to user configuration or
              kernel mapping tables might still happen as side effect
              of requested user operations, both privileged and
              unprivileged. To disable module auto-load feature please
              see sysctl.d(5) kernel.modules_disabled mechanism and
              /proc/sys/kernel/modules_disabled documentation. If
              turned on and if running in user mode, or in system
              mode, but without the CAP_SYS_ADMIN capability (e.g.
              setting User=), NoNewPrivileges=yes is implied.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          ProtectKernelLogs=
              Takes a boolean argument. If true, access to the kernel
              log ring buffer will be denied. It is recommended to
              turn this on for most services that do not need to read
              from or write to the kernel log ring buffer. Enabling
              this option removes CAP_SYSLOG from the capability
              bounding set for this unit, and installs a system call
              filter to block the syslog(2) system call (not to be
              confused with the libc API syslog(3) for userspace

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              logging). The kernel exposes its log buffer to userspace
              via /dev/kmsg and /proc/kmsg. If enabled, these are made
              inaccessible to all the processes in the unit.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          ProtectControlGroups=
              Takes a boolean argument. If true, the Linux Control
              Groups (cgroups(7)) hierarchies accessible through
              /sys/fs/cgroup/ will be made read-only to all processes
              of the unit. Except for container managers no services
              should require write access to the control groups hier-
              archies; it is hence recommended to turn this on for
              most services. For this setting the same restrictions
              regarding mount propagation and privileges apply as for
              ReadOnlyPaths= and related calls, see above. Defaults to
              off. If ProtectControlGroups= is set, MountAPIVFS=yes is
              implied.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          RestrictAddressFamilies=
              Restricts the set of socket address families accessible
              to the processes of this unit. Takes a space-separated
              list of address family names to allow-list, such as
              AF_UNIX, AF_INET or AF_INET6. When prefixed with ~ the
              listed address families will be applied as deny list,
              otherwise as allow list. Note that this restricts access
              to the socket(2) system call only. Sockets passed into
              the process by other means (for example, by using socket
              activation with socket units, see systemd.socket(5)) are
              unaffected. Also, sockets created with socketpair()
              (which creates connected AF_UNIX sockets only) are unaf-
              fected. Note that this option has no effect on 32-bit
              x86, s390, s390x, mips, mips-le, ppc, ppc-le, ppc64,
              ppc64-le and is ignored (but works correctly on other
              ABIs, including x86-64). Note that on systems supporting
              multiple ABIs (such as x86/x86-64) it is recommended to
              turn off alternative ABIs for services, so that they
              cannot be used to circumvent the restrictions of this
              option. Specifically, it is recommended to combine this
              option with SystemCallArchitectures=native or similar.
              If running in user mode, or in system mode, but without
              the CAP_SYS_ADMIN capability (e.g. setting User=nobody),
              NoNewPrivileges=yes is implied. By default, no restric-
              tions apply, all address families are accessible to pro-
              cesses. If assigned the empty string, any previous
              address family restriction changes are undone. This

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              setting does not affect commands prefixed with "+".

              Use this option to limit exposure of processes to remote
              access, in particular via exotic and sensitive network
              protocols, such as AF_PACKET. Note that in most cases,
              the local AF_UNIX address family should be included in
              the configured allow list as it is frequently used for
              local communication, including for syslog(2) logging.

          RestrictNamespaces=
              Restricts access to Linux namespace functionality for
              the processes of this unit. For details about Linux
              namespaces, see namespaces(7). Either takes a boolean
              argument, or a space-separated list of namespace type
              identifiers. If false (the default), no restrictions on
              namespace creation and switching are made. If true,
              access to any kind of namespacing is prohibited. Other-
              wise, a space-separated list of namespace type identi-
              fiers must be specified, consisting of any combination
              of: cgroup, ipc, net, mnt, pid, user and uts. Any names-
              pace type listed is made accessible to the unit's pro-
              cesses, access to namespace types not listed is prohib-
              ited (allow-listing). By prepending the list with a sin-
              gle tilde character ("~") the effect may be inverted:
              only the listed namespace types will be made inaccessi-
              ble, all unlisted ones are permitted (deny-listing). If
              the empty string is assigned, the default namespace
              restrictions are applied, which is equivalent to false.
              This option may appear more than once, in which case the
              namespace types are merged by OR, or by AND if the lines
              are prefixed with "~" (see examples below). Internally,
              this setting limits access to the unshare(2), clone(2)
              and setns(2) system calls, taking the specified flags
              parameters into account. Note that - if this option is
              used - in addition to restricting creation and switching
              of the specified types of namespaces (or all of them, if
              true) access to the setns() system call with a zero
              flags parameter is prohibited. This setting is only sup-
              ported on x86, x86-64, mips, mips-le, mips64, mips64-le,
              mips64-n32, mips64-le-n32, ppc64, ppc64-le, s390 and
              s390x, and enforces no restrictions on other architec-
              tures. If running in user mode, or in system mode, but
              without the CAP_SYS_ADMIN capability (e.g. setting
              User=), NoNewPrivileges=yes is implied.

              Example: if a unit has the following,

                  RestrictNamespaces=cgroup ipc
                  RestrictNamespaces=cgroup net

              then cgroup, ipc, and net are set. If the second line is
              prefixed with "~", e.g.,

     Page 33                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

                  RestrictNamespaces=cgroup ipc
                  RestrictNamespaces=~cgroup net

              then, only ipc is set.

          LockPersonality=
              Takes a boolean argument. If set, locks down the person-
              ality(2) system call so that the kernel execution domain
              may not be changed from the default or the personality
              selected with Personality= directive. This may be useful
              to improve security, because odd personality emulations
              may be poorly tested and source of vulnerabilities. If
              running in user mode, or in system mode, but without the
              CAP_SYS_ADMIN capability (e.g. setting User=),
              NoNewPrivileges=yes is implied.

          MemoryDenyWriteExecute=
              Takes a boolean argument. If set, attempts to create
              memory mappings that are writable and executable at the
              same time, or to change existing memory mappings to
              become executable, or mapping shared memory segments as
              executable are prohibited. Specifically, a system call
              filter is added that rejects mmap(2) system calls with
              both PROT_EXEC and PROT_WRITE set, mprotect(2) or
              pkey_mprotect(2) system calls with PROT_EXEC set and
              shmat(2) system calls with SHM_EXEC set. Note that this
              option is incompatible with programs and libraries that
              generate program code dynamically at runtime, including
              JIT execution engines, executable stacks, and code
              "trampoline" feature of various C compilers. This option
              improves service security, as it makes harder for soft-
              ware exploits to change running code dynamically. How-
              ever, the protection can be circumvented, if the service
              can write to a filesystem, which is not mounted with
              noexec (such as /dev/shm), or it can use memfd_create().
              This can be prevented by making such file systems inac-
              cessible to the service (e.g.
              InaccessiblePaths=/dev/shm) and installing further sys-
              tem call filters (SystemCallFilter=~memfd_create). Note
              that this feature is fully available on x86-64, and par-
              tially on x86. Specifically, the shmat() protection is
              not available on x86. Note that on systems supporting
              multiple ABIs (such as x86/x86-64) it is recommended to
              turn off alternative ABIs for services, so that they
              cannot be used to circumvent the restrictions of this
              option. Specifically, it is recommended to combine this
              option with SystemCallArchitectures=native or similar.
              If running in user mode, or in system mode, but without
              the CAP_SYS_ADMIN capability (e.g. setting User=),
              NoNewPrivileges=yes is implied.

          RestrictRealtime=

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              Takes a boolean argument. If set, any attempts to enable
              realtime scheduling in a process of the unit are
              refused. This restricts access to realtime task schedul-
              ing policies such as SCHED_FIFO, SCHED_RR or
              SCHED_DEADLINE. See sched(7) for details about these
              scheduling policies. If running in user mode, or in sys-
              tem mode, but without the CAP_SYS_ADMIN capability (e.g.
              setting User=), NoNewPrivileges=yes is implied. Realtime
              scheduling policies may be used to monopolize CPU time
              for longer periods of time, and may hence be used to
              lock up or otherwise trigger Denial-of-Service situa-
              tions on the system. It is hence recommended to restrict
              access to realtime scheduling to the few programs that
              actually require them. Defaults to off.

          RestrictSUIDSGID=
              Takes a boolean argument. If set, any attempts to set
              the set-user-ID (SUID) or set-group-ID (SGID) bits on
              files or directories will be denied (for details on
              these bits see inode(7)). If running in user mode, or in
              system mode, but without the CAP_SYS_ADMIN capability
              (e.g. setting User=), NoNewPrivileges=yes is implied. As
              the SUID/SGID bits are mechanisms to elevate privileges,
              and allows users to acquire the identity of other users,
              it is recommended to restrict creation of SUID/SGID
              files to the few programs that actually require them.
              Note that this restricts marking of any type of file
              system object with these bits, including both regular
              files and directories (where the SGID is a different
              meaning than for files, see documentation). This option
              is implied if DynamicUser= is enabled. Defaults to off.

          RemoveIPC=
              Takes a boolean parameter. If set, all System V and
              POSIX IPC objects owned by the user and group the pro-
              cesses of this unit are run as are removed when the unit
              is stopped. This setting only has an effect if at least
              one of User=, Group= and DynamicUser= are used. It has
              no effect on IPC objects owned by the root user. Specif-
              ically, this removes System V semaphores, as well as
              System V and POSIX shared memory segments and message
              queues. If multiple units use the same user or group the
              IPC objects are removed when the last of these units is
              stopped. This setting is implied if DynamicUser= is set.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          PrivateMounts=
              Takes a boolean parameter. If set, the processes of this
              unit will be run in their own private file system

     Page 35                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              (mount) namespace with all mount propagation from the
              processes towards the host's main file system namespace
              turned off. This means any file system mount points
              established or removed by the unit's processes will be
              private to them and not be visible to the host. However,
              file system mount points established or removed on the
              host will be propagated to the unit's processes. See
              mount_namespaces(7) for details on file system names-
              paces. Defaults to off.

              When turned on, this executes three operations for each
              invoked process: a new CLONE_NEWNS namespace is created,
              after which all existing mounts are remounted to
              MS_SLAVE to disable propagation from the unit's pro-
              cesses to the host (but leaving propagation in the oppo-
              site direction in effect). Finally, the mounts are
              remounted again to the propagation mode configured with
              MountFlags=, see below.

              File system namespaces are set up individually for each
              process forked off by the service manager. Mounts estab-
              lished in the namespace of the process created by Exec-
              StartPre= will hence be cleaned up automatically as soon
              as that process exits and will not be available to sub-
              sequent processes forked off for ExecStart= (and similar
              applies to the various other commands configured for
              units). Similarly, JoinsNamespaceOf= does not permit
              sharing kernel mount namespaces between units, it only
              enables sharing of the /tmp/ and /var/tmp/ directories.

              Other file system namespace unit settings - Private-
              Mounts=, PrivateTmp=, PrivateDevices=, ProtectSystem=,
              ProtectHome=, ReadOnlyPaths=, InaccessiblePaths=, Read-
              WritePaths=, ... - also enable file system namespacing
              in a fashion equivalent to this option. Hence it is pri-
              marily useful to explicitly request this behaviour if
              none of the other settings are used.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          MountFlags=
              Takes a mount propagation setting: shared, slave or pri-
              vate, which controls whether file system mount points in
              the file system namespaces set up for this unit's pro-
              cesses will receive or propagate mounts and unmounts
              from other file system namespaces. See mount(2) for
              details on mount propagation, and the three propagation
              flags in particular.

              This setting only controls the final propagation setting

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              in effect on all mount points of the file system names-
              pace created for each process of this unit. Other file
              system namespacing unit settings (see the discussion in
              PrivateMounts= above) will implicitly disable mount and
              unmount propagation from the unit's processes towards
              the host by changing the propagation setting of all
              mount points in the unit's file system namespace to
              slave first. Setting this option to shared does not
              reestablish propagation in that case.

              If not set en but file system namespaces are enabled
              through another file system namespace unit setting en
              shared mount propagation is used, but - as mentioned -
              as slave is applied first, propagation from the unit's
              processes to the host is still turned off.

              It is not recommended to use private mount propagation
              for units, as this means temporary mounts (such as
              removable media) of the host will stay mounted and thus
              indefinitely busy in forked off processes, as unmount
              propagation events won't be received by the file system
              namespace of the unit.

              Usually, it is best to leave this setting unmodified,
              and use higher level file system namespacing options
              instead, in particular PrivateMounts=, see above.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

     SYSTEM CALL FILTERING
          SystemCallFilter=
              Takes a space-separated list of system call names. If
              this setting is used, all system calls executed by the
              unit processes except for the listed ones will result in
              immediate process termination with the SIGSYS signal
              (allow-listing). (See SystemCallErrorNumber= below for
              changing the default action). If the first character of
              the list is "~", the effect is inverted: only the listed
              system calls will result in immediate process termina-
              tion (deny-listing). Deny-listed system calls and system
              call groups may optionally be suffixed with a colon
              (":") and "errno" error number (between 0 and 4095) or
              errno name such as EPERM, EACCES or EUCLEAN (see
              errno(3) for a full list). This value will be returned
              when a deny-listed system call is triggered, instead of
              terminating the processes immediately. Special setting
              "kill" can be used to explicitly specify killing. This
              value takes precedence over the one given in System-
              CallErrorNumber=, see below. If running in user mode, or
              in system mode, but without the CAP_SYS_ADMIN capability

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              (e.g. setting User=nobody), NoNewPrivileges=yes is
              implied. This feature makes use of the Secure Computing
              Mode 2 interfaces of the kernel ('seccomp filtering')
              and is useful for enforcing a minimal sandboxing envi-
              ronment. Note that the execve(), exit(), exit_group(),
              getrlimit(), rt_sigreturn(), sigreturn() system calls
              and the system calls for querying time and sleeping are
              implicitly allow-listed and do not need to be listed
              explicitly. This option may be specified more than once,
              in which case the filter masks are merged. If the empty
              string is assigned, the filter is reset, all prior
              assignments will have no effect. This does not affect
              commands prefixed with "+".

              Note that on systems supporting multiple ABIs (such as
              x86/x86-64) it is recommended to turn off alternative
              ABIs for services, so that they cannot be used to cir-
              cumvent the restrictions of this option. Specifically,
              it is recommended to combine this option with
              SystemCallArchitectures=native or similar.

              Note that strict system call filters may impact execu-
              tion and error handling code paths of the service invo-
              cation. Specifically, access to the execve() system call
              is required for the execution of the service binary - if
              it is blocked service invocation will necessarily fail.
              Also, if execution of the service binary fails for some
              reason (for example: missing service executable), the
              error handling logic might require access to an addi-
              tional set of system calls in order to process and log
              this failure correctly. It might be necessary to tem-
              porarily disable system call filters in order to sim-
              plify debugging of such failures.

              If you specify both types of this option (i.e.
              allow-listing and deny-listing), the first encountered
              will take precedence and will dictate the default action
              (termination or approval of a system call). Then the
              next occurrences of this option will add or delete the
              listed system calls from the set of the filtered system
              calls, depending of its type and the default action.
              (For example, if you have started with an allow list
              rule for read() and write(), and right after it add a
              deny list rule for write(), then write() will be removed
              from the set.)

              As the number of possible system calls is large, prede-
              fined sets of system calls are provided. A set starts
              with "@" character, followed by name of the set.

              Table 4. Currently predefined system call sets allbox
              tab(:); lB lB.  T{ Set T}:T{ Description T} l l l l l l

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              l l l l l l l l l l l l l l l l l l l l l l l l l l l l
              l l l l l l l l l l l l l l l l l l l l.  T{ @aio T}:T{
              Asynchronous I/O (io_setup(2), io_submit(2), and related
              calls) T} T{ @basic-io T}:T{ System calls for basic I/O:
              reading, writing, seeking, file descriptor duplication
              and closing (read(2), write(2), and related calls) T} T{
              @chown T}:T{ Changing file ownership (chown(2), fchow-
              nat(2), and related calls) T} T{ @clock T}:T{ System
              calls for changing the system clock (adjtimex(2), set-
              timeofday(2), and related calls) T} T{ @cpu-emulation
              T}:T{ System calls for CPU emulation functionality
              (vm86(2) and related calls) T} T{ @debug T}:T{ Debug-
              ging, performance monitoring and tracing functionality
              (ptrace(2), perf_event_open(2) and related calls) T} T{
              @file-system T}:T{ File system operations: opening, cre-
              ating files and directories for read and write, renaming
              and removing them, reading file properties, or creating
              hard and symbolic links T} T{ @io-event T}:T{ Event loop
              system calls (poll(2), select(2), epoll(7), eventfd(2)
              and related calls) T} T{ @ipc T}:T{ Pipes, SysV IPC,
              POSIX Message Queues and other IPC (mq_overview(7),
              svipc(7)) T} T{ @keyring T}:T{ Kernel keyring access
              (keyctl(2) and related calls) T} T{ @memlock T}:T{ Lock-
              ing of memory in RAM (mlock(2), mlockall(2) and related
              calls) T} T{ @module T}:T{ Loading and unloading of ker-
              nel modules (init_module(2), delete_module(2) and
              related calls) T} T{ @mount T}:T{ Mounting and unmount-
              ing of file systems (mount(2), chroot(2), and related
              calls) T} T{ @network-io T}:T{ Socket I/O (including
              local AF_UNIX): socket(7), unix(7) T} T{ @obsolete T}:T{
              Unusual, obsolete or unimplemented (create_module(2),
              gtty(2), ...)  T} T{ @privileged T}:T{ All system calls
              which need super-user capabilities (capabilities(7)) T}
              T{ @process T}:T{ Process control, execution, namespac-
              ing operations (clone(2), kill(2), namespaces(7), ...)
              T} T{ @raw-io T}:T{ Raw I/O port access (ioperm(2),
              iopl(2), pciconfig_read(), ...)  T} T{ @reboot T}:T{
              System calls for rebooting and reboot preparation
              (reboot(2), kexec(), ...)  T} T{ @resources T}:T{ System
              calls for changing resource limits, memory and schedul-
              ing parameters (setrlimit(2), setpriority(2), ...)  T}
              T{ @setuid T}:T{ System calls for changing user ID and
              group ID credentials, (setuid(2), setgid(2), setre-
              suid(2), ...)  T} T{ @signal T}:T{ System calls for
              manipulating and handling process signals (signal(2),
              sigprocmask(2), ...)  T} T{ @swap T}:T{ System calls for
              enabling/disabling swap devices (swapon(2), swapoff(2))
              T} T{ @sync T}:T{ Synchronizing files and memory to disk
              (fsync(2), msync(2), and related calls) T} T{
              @system-service T}:T{ A reasonable set of system calls
              used by common system services, excluding any special
              purpose calls. This is the recommended starting point

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              for allow-listing system calls for system services, as
              it contains what is typically needed by system services,
              but excludes overly specific interfaces. For example,
              the following APIs are excluded: "@clock", "@mount",
              "@swap", "@reboot".  T} T{ @timer T}:T{ System calls for
              scheduling operations by time (alarm(2),
              timer_create(2), ...)  T} T{ @known T}:T{ All system
              calls defined by the kernel. This list is defined stati-
              cally in systemd based on a kernel version that was
              available when this systemd version was released. It
              will become progressively more out-of-date as the kernel
              is updated.  T}

              Note, that as new system calls are added to the kernel,
              additional system calls might be added to the groups
              above. Contents of the sets may also change between sys-
              temd versions. In addition, the list of system calls
              depends on the kernel version and architecture for which
              systemd was compiled. Use systemd-analyze syscall-filter
              to list the actual list of system calls in each filter.

              Generally, allow-listing system calls (rather than
              deny-listing) is the safer mode of operation. It is rec-
              ommended to enforce system call allow lists for all
              long-running system services. Specifically, the follow-
              ing lines are a relatively safe basic choice for the
              majority of system services:

                  [Service]
                  SystemCallFilter=@system-service
                  SystemCallErrorNumber=EPERM

              Note that various kernel system calls are defined redun-
              dantly: there are multiple system calls for executing
              the same operation. For example, the pidfd_send_signal()
              system call may be used to execute operations similar to
              what can be done with the older kill() system call,
              hence blocking the latter without the former only pro-
              vides weak protection. Since new system calls are added
              regularly to the kernel as development progresses, keep-
              ing system call deny lists comprehensive requires con-
              stant work. It is thus recommended to use allow-listing
              instead, which offers the benefit that new system calls
              are by default implicitly blocked until the allow list
              is updated.

              Also note that a number of system calls are required to
              be accessible for the dynamic linker to work. The
              dynamic linker is required for running most regular pro-
              grams (specifically: all dynamic ELF binaries, which is
              how most distributions build packaged programs). This
              means that blocking these system calls (which include

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              open(), openat() or mmap()) will make most programs typ-
              ically shipped with generic distributions unusable.

              It is recommended to combine the file system namespacing
              related options with SystemCallFilter=~@mount, in order
              to prohibit the unit's processes to undo the mappings.
              Specifically these are the options PrivateTmp=, Privat-
              eDevices=, ProtectSystem=, ProtectHome=, ProtectKernel-
              Tunables=, ProtectControlGroups=, ProtectKernelLogs=,
              ProtectClock=, ReadOnlyPaths=, InaccessiblePaths= and
              ReadWritePaths=.

          SystemCallErrorNumber=
              Takes an "errno" error number (between 1 and 4095) or
              errno name such as EPERM, EACCES or EUCLEAN, to return
              when the system call filter configured with SystemCall-
              Filter= is triggered, instead of terminating the process
              immediately. See errno(3) for a full list of error
              codes. When this setting is not used, or when the empty
              string or the special setting "kill" is assigned, the
              process will be terminated immediately when the filter
              is triggered.

          SystemCallArchitectures=
              Takes a space-separated list of architecture identifiers
              to include in the system call filter. The known archi-
              tecture identifiers are the same as for ConditionArchi-
              tecture= described in systemd.unit(5), as well as x32,
              mips64-n32, mips64-le-n32, and the special identifier
              native. The special identifier native implicitly maps to
              the native architecture of the system (or more pre-
              cisely: to the architecture the system manager is com-
              piled for). If running in user mode, or in system mode,
              but without the CAP_SYS_ADMIN capability (e.g. setting
              User=nobody), NoNewPrivileges=yes is implied. By
              default, this option is set to the empty list, i.e. no
              filtering is applied.

              If this setting is used, processes of this unit will
              only be permitted to call native system calls, and sys-
              tem calls of the specified architectures. For the pur-
              poses of this option, the x32 architecture is treated as
              including x86-64 system calls. However, this setting
              still fulfills its purpose, as explained below, on x32.

              System call filtering is not equally effective on all
              architectures. For example, on x86 filtering of network
              socket-related calls is not possible, due to ABI limita-
              tions - a limitation that x86-64 does not have, however.
              On systems supporting multiple ABIs at the same time -
              such as x86/x86-64 - it is hence recommended to limit
              the set of permitted system call architectures so that

     Page 41                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              secondary ABIs may not be used to circumvent the
              restrictions applied to the native ABI of the system. In
              particular, setting SystemCallArchitectures=native is a
              good choice for disabling non-native ABIs.

              System call architectures may also be restricted
              system-wide via the SystemCallArchitectures= option in
              the global configuration. See systemd-system.conf(5) for
              details.

          SystemCallLog=
              Takes a space-separated list of system call names. If
              this setting is used, all system calls executed by the
              unit processes for the listed ones will be logged. If
              the first character of the list is "~", the effect is
              inverted: all system calls except the listed system
              calls will be logged. If running in user mode, or in
              system mode, but without the CAP_SYS_ADMIN capability
              (e.g. setting User=nobody), NoNewPrivileges=yes is
              implied. This feature makes use of the Secure Computing
              Mode 2 interfaces of the kernel ('seccomp filtering')
              and is useful for auditing or setting up a minimal sand-
              boxing environment. This option may be specified more
              than once, in which case the filter masks are merged. If
              the empty string is assigned, the filter is reset, all
              prior assignments will have no effect. This does not
              affect commands prefixed with "+".

     ENVIRONMENT
          Environment=
              Sets environment variables for executed processes. Takes
              a space-separated list of variable assignments. This
              option may be specified more than once, in which case
              all listed variables will be set. If the same variable
              is set twice, the later setting will override the ear-
              lier setting. If the empty string is assigned to this
              option, the list of environment variables is reset, all
              prior assignments have no effect. Variable expansion is
              not performed inside the strings, however, specifier
              expansion is possible. The "$" character has no special
              meaning. If you need to assign a value containing spaces
              or the equals sign to a variable, use double quotes (")
              for the assignment.

              The names of the variables can contain ASCII letters,
              digits, and the underscore character. Variable names
              cannot be empty or start with a digit. In variable val-
              ues, most characters are allowed, but non-printable
              characters are currently rejected.

              Example:

     Page 42                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

                  Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"

              gives three variables "VAR1", "VAR2", "VAR3" with the
              values "word1 word2", "word3", "$word 5 6".

              See environ(7) for details about environment variables.

              Note that environment variables are not suitable for
              passing secrets (such as passwords, key material, ...)
              to service processes. Environment variables set for a
              unit are exposed to unprivileged clients via D-Bus IPC,
              and generally not understood as being data that requires
              protection. Moreover, environment variables are propa-
              gated down the process tree, including across security
              boundaries (such as setuid/setgid executables), and
              hence might leak to processes that should not have
              access to the secret data. Use LoadCredential= (see
              below) to pass data to unit processes securely.

          EnvironmentFile=
              Similar to Environment= but reads the environment vari-
              ables from a text file. The text file should contain
              new-line-separated variable assignments. Empty lines,
              lines without an "=" separator, or lines starting with ;
              or # will be ignored, which may be used for commenting.
              A line ending with a backslash will be concatenated with
              the following one, allowing multiline variable defini-
              tions. The parser strips leading and trailing whitespace
              from the values of assignments, unless you use double
              quotes (").

              m[blue]C escapesm[][7] are supported, but not
              m[blue]most control charactersm[][8].  "\t" and "\n" can
              be used to insert tabs and newlines within Environment-
              File=.

              The argument passed should be an absolute filename or
              wildcard expression, optionally prefixed with "-", which
              indicates that if the file does not exist, it will not
              be read and no error or warning message is logged. This
              option may be specified more than once in which case all
              specified files are read. If the empty string is
              assigned to this option, the list of file to read is
              reset, all prior assignments have no effect.

              The files listed with this directive will be read
              shortly before the process is executed (more specifi-
              cally, after all processes from a previous unit state
              terminated. This means you can generate these files in
              one unit state, and read it with this option in the
              next. The files are read from the file system of the
              service manager, before any file system changes like

     Page 43                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              bind mounts take place).

              Settings from these files override settings made with
              Environment=. If the same variable is set twice from
              these files, the files will be read in the order they
              are specified and the later setting will override the
              earlier setting.

          PassEnvironment=
              Pass environment variables set for the system service
              manager to executed processes. Takes a space-separated
              list of variable names. This option may be specified
              more than once, in which case all listed variables will
              be passed. If the empty string is assigned to this
              option, the list of environment variables to pass is
              reset, all prior assignments have no effect. Variables
              specified that are not set for the system manager will
              not be passed and will be silently ignored. Note that
              this option is only relevant for the system service man-
              ager, as system services by default do not automatically
              inherit any environment variables set for the service
              manager itself. However, in case of the user service
              manager all environment variables are passed to the exe-
              cuted processes anyway, hence this option is without
              effect for the user service manager.

              Variables set for invoked processes due to this setting
              are subject to being overridden by those configured with
              Environment= or EnvironmentFile=.

              m[blue]C escapesm[][7] are supported, but not
              m[blue]most control charactersm[][8].  "\t" and "\n" can
              be used to insert tabs and newlines within Environment-
              File=.

              Example:

                  PassEnvironment=VAR1 VAR2 VAR3

              passes three variables "VAR1", "VAR2", "VAR3" with the
              values set for those variables in PID1.

              See environ(7) for details about environment variables.

          UnsetEnvironment=
              Explicitly unset environment variable assignments that
              would normally be passed from the service manager to
              invoked processes of this unit. Takes a space-separated
              list of variable names or variable assignments. This
              option may be specified more than once, in which case
              all listed variables/assignments will be unset. If the
              empty string is assigned to this option, the list of

     Page 44                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              environment variables/assignments to unset is reset. If
              a variable assignment is specified (that is: a variable
              name, followed by "=", followed by its value), then any
              environment variable matching this precise assignment is
              removed. If a variable name is specified (that is a
              variable name without any following "=" or value), then
              any assignment matching the variable name, regardless of
              its value is removed. Note that the effect of UnsetEnvi-
              ronment= is applied as final step when the environment
              list passed to executed processes is compiled. That
              means it may undo assignments from any configuration
              source, including assignments made through Environment=
              or EnvironmentFile=, inherited from the system manager's
              global set of environment variables, inherited via
              PassEnvironment=, set by the service manager itself
              (such as $NOTIFY_SOCKET and such), or set by a PAM mod-
              ule (in case PAMName= is used).

              See "Environment Variables in Spawned Processes" below
              for a description of how those settings combine to form
              the inherited environment. See environ(7) for general
              information about environment variables.

     LOGGING AND STANDARD INPUT/OUTPUT
          StandardInput=
              Controls where file descriptor 0 (STDIN) of the executed
              processes is connected to. Takes one of null, tty,
              tty-force, tty-fail, data, file:path, socket or fd:name.

              If null is selected, standard input will be connected to
              /dev/null, i.e. all read attempts by the process will
              result in immediate EOF.

              If tty is selected, standard input is connected to a TTY
              (as configured by TTYPath=, see below) and the executed
              process becomes the controlling process of the terminal.
              If the terminal is already being controlled by another
              process, the executed process waits until the current
              controlling process releases the terminal.

              tty-force is similar to tty, but the executed process is
              forcefully and immediately made the controlling process
              of the terminal, potentially removing previous control-
              ling processes from the terminal.

              tty-fail is similar to tty, but if the terminal already
              has a controlling process start-up of the executed pro-
              cess fails.

              The data option may be used to configure arbitrary tex-
              tual or binary data to pass via standard input to the
              executed process. The data to pass is configured via

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              StandardInputText=/StandardInputData= (see below). Note
              that the actual file descriptor type passed (memory
              file, regular file, UNIX pipe, ...) might depend on the
              kernel and available privileges. In any case, the file
              descriptor is read-only, and when read returns the spec-
              ified data followed by EOF.

              The file:path option may be used to connect a specific
              file system object to standard input. An absolute path
              following the ":" character is expected, which may refer
              to a regular file, a FIFO or special file. If an AF_UNIX
              socket in the file system is specified, a stream socket
              is connected to it. The latter is useful for connecting
              standard input of processes to arbitrary system ser-
              vices.

              The socket option is valid in socket-activated services
              only, and requires the relevant socket unit file (see
              systemd.socket(5) for details) to have Accept=yes set,
              or to specify a single socket only. If this option is
              set, standard input will be connected to the socket the
              service was activated from, which is primarily useful
              for compatibility with daemons designed for use with the
              traditional inetd(8) socket activation daemon.

              The fd:name option connects standard input to a spe-
              cific, named file descriptor provided by a socket unit.
              The name may be specified as part of this option, fol-
              lowing a ":" character (e.g.  "fd:foobar"). If no name
              is specified, the name "stdin" is implied (i.e.  "fd" is
              equivalent to "fd:stdin"). At least one socket unit
              defining the specified name must be provided via the
              Sockets= option, and the file descriptor name may differ
              from the name of its containing socket unit. If multiple
              matches are found, the first one will be used. See
              FileDescriptorName= in systemd.socket(5) for more
              details about named file descriptors and their ordering.

              This setting defaults to null, unless
              StandardInputText=/StandardInputData= are set, in which
              case it defaults to data.

          StandardOutput=
              Controls where file descriptor 1 (stdout) of the exe-
              cuted processes is connected to. Takes one of inherit,
              null, tty, journal, kmsg, journal+console, kmsg+console,
              file:path, append:path, socket or fd:name.

              inherit duplicates the file descriptor of standard input
              for standard output.

              null connects standard output to /dev/null, i.e.

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              everything written to it will be lost.

              tty connects standard output to a tty (as configured via
              TTYPath=, see below). If the TTY is used for output
              only, the executed process will not become the control-
              ling process of the terminal, and will not fail or wait
              for other processes to release the terminal.

              journal connects standard output with the journal, which
              is accessible via journalctl(1). Note that everything
              that is written to kmsg (see below) is implicitly stored
              in the journal as well, the specific option listed below
              is hence a superset of this one. (Also note that any
              external, additional syslog daemons receive their log
              data from the journal, too, hence this is the option to
              use when logging shall be processed with such a daemon.)

              kmsg connects standard output with the kernel log buffer
              which is accessible via dmesg(1), in addition to the
              journal. The journal daemon might be configured to send
              all logs to kmsg anyway, in which case this option is no
              different from journal.

              journal+console and kmsg+console work in a similar way
              as the two options above but copy the output to the sys-
              tem console as well.

              The file:path option may be used to connect a specific
              file system object to standard output. The semantics are
              similar to the same option of StandardInput=, see above.
              If path refers to a regular file on the filesystem, it
              is opened (created if it doesn't exist yet) for writing
              at the beginning of the file, but without truncating it.
              If standard input and output are directed to the same
              file path, it is opened only once, for reading as well
              as writing and duplicated. This is particularly useful
              when the specified path refers to an AF_UNIX socket in
              the file system, as in that case only a single stream
              connection is created for both input and output.

              append:path is similar to file:path above, but it opens
              the file in append mode.

              socket connects standard output to a socket acquired via
              socket activation. The semantics are similar to the same
              option of StandardInput=, see above.

              The fd:name option connects standard output to a spe-
              cific, named file descriptor provided by a socket unit.
              A name may be specified as part of this option, follow-
              ing a ":" character (e.g.  "fd:foobar"). If no name is
              specified, the name "stdout" is implied (i.e.  "fd" is

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              equivalent to "fd:stdout"). At least one socket unit
              defining the specified name must be provided via the
              Sockets= option, and the file descriptor name may differ
              from the name of its containing socket unit. If multiple
              matches are found, the first one will be used. See
              FileDescriptorName= in systemd.socket(5) for more
              details about named descriptors and their ordering.

              If the standard output (or error output, see below) of a
              unit is connected to the journal or the kernel log
              buffer, the unit will implicitly gain a dependency of
              type After= on systemd-journald.socket (also see the
              "Implicit Dependencies" section above). Also note that
              in this case stdout (or stderr, see below) will be an
              AF_UNIX stream socket, and not a pipe or FIFO that can
              be re-opened. This means when executing shell scripts
              the construct echo "hello" > /dev/stderr for writing
              text to stderr will not work. To mitigate this use the
              construct echo "hello" >&2 instead, which is mostly
              equivalent and avoids this pitfall.

              This setting defaults to the value set with DefaultStan-
              dardOutput= in systemd-system.conf(5), which defaults to
              journal. Note that setting this parameter might result
              in additional dependencies to be added to the unit (see
              above).

          StandardError=
              Controls where file descriptor 2 (stderr) of the exe-
              cuted processes is connected to. The available options
              are identical to those of StandardOutput=, with some
              exceptions: if set to inherit the file descriptor used
              for standard output is duplicated for standard error,
              while fd:name will use a default file descriptor name of
              "stderr".

              This setting defaults to the value set with DefaultStan-
              dardError= in systemd-system.conf(5), which defaults to
              inherit. Note that setting this parameter might result
              in additional dependencies to be added to the unit (see
              above).

          StandardInputText=, StandardInputData=
              Configures arbitrary textual or binary data to pass via
              file descriptor 0 (STDIN) to the executed processes.
              These settings have no effect unless StandardInput= is
              set to data (which is the default if StandardInput= is
              not set otherwise, but
              StandardInputText=/StandardInputData= is). Use this
              option to embed process input data directly in the unit
              file.

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              StandardInputText= accepts arbitrary textual data.
              C-style escapes for special characters as well as the
              usual "%"-specifiers are resolved. Each time this set-
              ting is used the specified text is appended to the
              per-unit data buffer, followed by a newline character
              (thus every use appends a new line to the end of the
              buffer). Note that leading and trailing whitespace of
              lines configured with this option is removed. If an
              empty line is specified the buffer is cleared (hence, in
              order to insert an empty line, add an additional "\n" to
              the end or beginning of a line).

              StandardInputData= accepts arbitrary binary data,
              encoded in m[blue]Base64m[][9]. No escape sequences or
              specifiers are resolved. Any whitespace in the encoded
              version is ignored during decoding.

              Note that StandardInputText= and StandardInputData=
              operate on the same data buffer, and may be mixed in
              order to configure both binary and textual data for the
              same input stream. The textual or binary data is joined
              strictly in the order the settings appear in the unit
              file. Assigning an empty string to either will reset the
              data buffer.

              Please keep in mind that in order to maintain readabil-
              ity long unit file settings may be split into multiple
              lines, by suffixing each line (except for the last) with
              a "\" character (see systemd.unit(5) for details). This
              is particularly useful for large data configured with
              these two options. Example:

                  ...
                  StandardInput=data
                  StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy4KSWNrIGtpZWtl \
                                    LCBzdGF1bmUsIHd1bmRyZSBtaXIsCnVmZiBlZW1hbCBqZWh0IHNlIHVmZiBkaWUgVMO8ci4KTmFu \
                                    dSwgZGVuayBpY2ssIGljayBkZW5rIG5hbnUhCkpldHogaXNzZSB1ZmYsIGVyc2NodCB3YXIgc2Ug \
                                    enUhCkljayBqZWhlIHJhdXMgdW5kIGJsaWNrZSDigJQKdW5kIHdlciBzdGVodCBkcmF1w59lbj8g \
                                    SWNrZSEK
                  ...

          LogLevelMax=
              Configures filtering by log level of log messages gener-
              ated by this unit. Takes a syslog log level, one of
              emerg (lowest log level, only highest priority mes-
              sages), alert, crit, err, warning, notice, info, debug
              (highest log level, also lowest priority messages). See
              syslog(3) for details. By default no filtering is
              applied (i.e. the default maximum log level is debug).
              Use this option to configure the logging system to drop
              log messages of a specific service above the specified
              level. For example, set LogLevelMax=info in order to

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              turn off debug logging of a particularly chatty unit.
              Note that the configured level is applied to any log
              messages written by any of the processes belonging to
              this unit, sent via any supported logging protocol. The
              filtering is applied early in the logging pipeline,
              before any kind of further processing is done. Moreover,
              messages which pass through this filter successfully
              might still be dropped by filters applied at a later
              stage in the logging subsystem. For example, MaxLevel-
              Store= configured in journald.conf(5) might prohibit
              messages of higher log levels to be stored on disk, even
              though the per-unit LogLevelMax= permitted it to be pro-
              cessed.

          LogExtraFields=
              Configures additional log metadata fields to include in
              all log records generated by processes associated with
              this unit. This setting takes one or more journal field
              assignments in the format "FIELD=VALUE" separated by
              whitespace. See systemd.journal-fields(7) for details on
              the journal field concept. Even though the underlying
              journal implementation permits binary field values, this
              setting accepts only valid UTF-8 values. To include
              space characters in a journal field value, enclose the
              assignment in double quotes (").  The usual specifiers
              are expanded in all assignments (see below). Note that
              this setting is not only useful for attaching additional
              metadata to log records of a unit, but given that all
              fields and values are indexed may also be used to imple-
              ment cross-unit log record matching. Assign an empty
              string to reset the list.

          LogRateLimitIntervalSec=, LogRateLimitBurst=
              Configures the rate limiting that is applied to messages
              generated by this unit. If, in the time interval defined
              by LogRateLimitIntervalSec=, more messages than speci-
              fied in LogRateLimitBurst= are logged by a service, all
              further messages within the interval are dropped until
              the interval is over. A message about the number of
              dropped messages is generated. The time specification
              for LogRateLimitIntervalSec= may be specified in the
              following units: "s", "min", "h", "ms", "us" (see
              systemd.time(7) for details). The default settings are
              set by RateLimitIntervalSec= and RateLimitBurst= config-
              ured in journald.conf(5).

          LogNamespace=
              Run the unit's processes in the specified journal names-
              pace. Expects a short user-defined string identifying
              the namespace. If not used the processes of the service
              are run in the default journal namespace, i.e. their log
              stream is collected and processed by

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              systemd-journald.service. If this option is used any log
              data generated by processes of this unit (regardless if
              via the syslog(), journal native logging or
              stdout/stderr logging) is collected and processed by an
              instance of the systemd-journald@.service template unit,
              which manages the specified namespace. The log data is
              stored in a data store independent from the default log
              namespace's data store. See systemd-journald.service(8)
              for details about journal namespaces.

              Internally, journal namespaces are implemented through
              Linux mount namespacing and over-mounting the directory
              that contains the relevant AF_UNIX sockets used for log-
              ging in the unit's mount namespace. Since mount names-
              paces are used this setting disconnects propagation of
              mounts from the unit's processes to the host, similar to
              how ReadOnlyPaths= and similar settings (see above)
              work. Journal namespaces may hence not be used for ser-
              vices that need to establish mount points on the host.

              When this option is used the unit will automatically
              gain ordering and requirement dependencies on the two
              socket units associated with the
              systemd-journald@.service instance so that they are
              automatically established prior to the unit starting up.
              Note that when this option is used log output of this
              service does not appear in the regular journalctl(1)
              output, unless the --namespace= option is used.

              This option is only available for system services and is
              not supported for services running in per-user instances
              of the service manager.

          SyslogIdentifier=
              Sets the process name ("syslog tag") to prefix log lines
              sent to the logging system or the kernel log buffer
              with. If not set, defaults to the process name of the
              executed process. This option is only useful when Stan-
              dardOutput= or StandardError= are set to journal or kmsg
              (or to the same settings in combination with +console)
              and only applies to log messages written to stdout or
              stderr.

          SyslogFacility=
              Sets the syslog facility identifier to use when logging.
              One of kern, user, mail, daemon, auth, syslog, lpr,
              news, uucp, cron, authpriv, ftp, local0, local1, local2,
              local3, local4, local5, local6 or local7. See syslog(3)
              for details. This option is only useful when Standard-
              Output= or StandardError= are set to journal or kmsg (or
              to the same settings in combination with +console), and
              only applies to log messages written to stdout or

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              stderr. Defaults to daemon.

          SyslogLevel=
              The default syslog log level to use when logging to the
              logging system or the kernel log buffer. One of emerg,
              alert, crit, err, warning, notice, info, debug. See sys-
              log(3) for details. This option is only useful when
              StandardOutput= or StandardError= are set to journal or
              kmsg (or to the same settings in combination with +con-
              sole), and only applies to log messages written to std-
              out or stderr. Note that individual lines output by exe-
              cuted processes may be prefixed with a different log
              level which can be used to override the default log
              level specified here. The interpretation of these pre-
              fixes may be disabled with SyslogLevelPrefix=, see
              below. For details, see sd-daemon(3). Defaults to info.

          SyslogLevelPrefix=
              Takes a boolean argument. If true and StandardOutput= or
              StandardError= are set to journal or kmsg (or to the
              same settings in combination with +console), log lines
              written by the executed process that are prefixed with a
              log level will be processed with this log level set but
              the prefix removed. If set to false, the interpretation
              of these prefixes is disabled and the logged lines are
              passed on as-is. This only applies to log messages writ-
              ten to stdout or stderr. For details about this prefix-
              ing see sd-daemon(3). Defaults to true.

          TTYPath=
              Sets the terminal device node to use if standard input,
              output, or error are connected to a TTY (see above).
              Defaults to /dev/console.

          TTYReset=
              Reset the terminal device specified with TTYPath= before
              and after execution. Defaults to "no".

          TTYVHangup=
              Disconnect all clients which have opened the terminal
              device specified with TTYPath= before and after execu-
              tion. Defaults to "no".

          TTYVTDisallocate=
              If the terminal device specified with TTYPath= is a vir-
              tual console terminal, try to deallocate the TTY before
              and after execution. This ensures that the screen and
              scrollback buffer is cleared. Defaults to "no".

     CREDENTIALS
          LoadCredential=ID:PATH
              Pass a credential to the unit. Credentials are

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              limited-size binary or textual objects that may be
              passed to unit processes. They are primarily used for
              passing cryptographic keys (both public and private) or
              certificates, user account information or identity
              information from host to services. The data is accessi-
              ble from the unit's processes via the file system, at a
              read-only location that (if possible and permitted) is
              backed by non-swappable memory. The data is only acces-
              sible to the user associated with the unit, via the
              User=/DynamicUser= settings (as well as the superuser).
              When available, the location of credentials is exported
              as the $CREDENTIALS_DIRECTORY environment variable to
              the unit's processes.

              The LoadCredential= setting takes a textual ID to use as
              name for a credential plus a file system path. The ID
              must be a short ASCII string suitable as filename in the
              filesystem, and may be chosen freely by the user. If the
              specified path is absolute it is opened as regular file
              and the credential data is read from it. If the absolute
              path refers to an AF_UNIX stream socket in the file sys-
              tem a connection is made to it (only once at unit
              start-up) and the credential data read from the connec-
              tion, providing an easy IPC integration point for dynam-
              ically providing credentials from other services. If the
              specified path is not absolute and itself qualifies as
              valid credential identifier it is understood to refer to
              a credential that the service manager itself received
              via the $CREDENTIALS_DIRECTORY environment variable,
              which may be used to propagate credentials from an
              invoking environment (e.g. a container manager that
              invoked the service manager) into a service. The con-
              tents of the file/socket may be arbitrary binary or tex-
              tual data, including newline characters and NUL bytes.
              This option may be used multiple times, each time defin-
              ing an additional credential to pass to the unit.

              The credential files/IPC sockets must be accessible to
              the service manager, but don't have to be directly
              accessible to the unit's processes: the credential data
              is read and copied into separate, read-only copies for
              the unit that are accessible to appropriately privileged
              processes. This is particularly useful in combination
              with DynamicUser= as this way privileged data can be
              made available to processes running under a dynamic UID
              (i.e. not a previously known one) without having to open
              up access to all users.

              In order to reference the path a credential may be read
              from within a ExecStart= command line use
              "${CREDENTIALS_DIRECTORY}/mycred", e.g.  "ExecStart=cat
              ${CREDENTIALS_DIRECTORY}/mycred".

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              Currently, an accumulated credential size limit of 1M
              bytes per unit is enforced.

              If referencing an AF_UNIX stream socket to connect to,
              the connection will originate from an abstract namespace
              socket, that includes information about the unit and the
              credential ID in its socket name. Use getpeername(2) to
              query this information. The returned socket name is for-
              matted as NUL RANDOM "/unit/" UNIT "/" ID, i.e. a NUL
              byte (as required for abstract namespace socket names),
              followed by a random string (consisting of alphadecimal
              characters), followed by the literal string "/unit/",
              followed by the requesting unit name, followed by the
              literal character "/", followed by the textual creden-
              tial ID requested. Example:
              "\0adf9d86b6eda275e/unit/foobar.service/credx" in case
              the credential "credx" is requested for a unit
              "foobar.service". This functionality is useful for using
              a single listening socket to serve credentials to multi-
              ple consumers.

          SetCredential=ID:VALUE
              The SetCredential= setting is similar to LoadCredential=
              but accepts a literal value to use as data for the cre-
              dential, instead of a file system path to read the data
              from. Do not use this option for data that is supposed
              to be secret, as it is accessible to unprivileged pro-
              cesses via IPC. It's only safe to use this for user IDs,
              public key material and similar non-sensitive data. For
              everything else use LoadCredential=. In order to embed
              binary data into the credential data use C-style escap-
              ing (i.e.  "\n" to embed a newline, or "\x00" to embed a
              NUL byte).

              If a credential of the same ID is listed in both Load-
              Credential= and SetCredential=, the latter will act as
              default if the former cannot be retrieved. In this case
              not being able to retrieve the credential from the path
              specified in LoadCredential= is not considered fatal.

     SYSTEM V COMPATIBILITY
          UtmpIdentifier=
              Takes a four character identifier string for an utmp(5)
              and wtmp entry for this service. This should only be set
              for services such as getty implementations (such as
              agetty(8)) where utmp/wtmp entries must be created and
              cleared before and after execution, or for services that
              shall be executed as if they were run by a getty process
              (see below). If the configured string is longer than
              four characters, it is truncated and the terminal four
              characters are used. This setting interprets %I style
              string replacements. This setting is unset by default,

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              i.e. no utmp/wtmp entries are created or cleaned up for
              this service.

          UtmpMode=
              Takes one of "init", "login" or "user". If UtmpIdenti-
              fier= is set, controls which type of utmp(5)/wtmp
              entries for this service are generated. This setting has
              no effect unless UtmpIdentifier= is set too. If "init"
              is set, only an INIT_PROCESS entry is generated and the
              invoked process must implement a getty-compatible
              utmp/wtmp logic. If "login" is set, first an
              INIT_PROCESS entry, followed by a LOGIN_PROCESS entry is
              generated. In this case, the invoked process must imple-
              ment a login(1)-compatible utmp/wtmp logic. If "user" is
              set, first an INIT_PROCESS entry, then a LOGIN_PROCESS
              entry and finally a USER_PROCESS entry is generated. In
              this case, the invoked process may be any process that
              is suitable to be run as session leader. Defaults to
              "init".

     ENVIRONMENT VARIABLES IN SPAWNED PROCESSES
          Processes started by the service manager are executed with
          an environment variable block assembled from multiple
          sources. Processes started by the system service manager
          generally do not inherit environment variables set for the
          service manager itself (but this may be altered via PassEn-
          vironment=), but processes started by the user service man-
          ager instances generally do inherit all environment vari-
          ables set for the service manager itself.

          For each invoked process the list of environment variables
          set is compiled from the following sources:

          +o   Variables globally configured for the service manager,
              using the DefaultEnvironment= setting in systemd-
              system.conf(5), the kernel command line option
              systemd.setenv= understood by systemd(1), or via system-
              ctl(1) set-environment verb.

          +o   Variables defined by the service manager itself (see the
              list below).

          +o   Variables set in the service manager's own environment
              variable block (subject to PassEnvironment= for the sys-
              tem service manager).

          +o   Variables set via Environment= in the unit file.

          +o   Variables read from files specified via EnvironmentFile=
              in the unit file.

          +o   Variables set by any PAM modules in case PAMName= is in

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              effect, cf. pam_env(8).

          If the same environment variable is set by multiple of these
          sources, the later source - according to the order of the
          list above - wins. Note that as the final step all variables
          listed in UnsetEnvironment= are removed from the compiled
          environment variable list, immediately before it is passed
          to the executed process.

          The general philosophy is to expose a small curated list of
          environment variables to processes. Services started by the
          system manager (PID 1) will be started, without additional
          service-specific configuration, with just a few environment
          variables. The user manager inherits environment variables
          as any other system service, but in addition may receive
          additional environment variables from PAM, and, typically,
          additional imported variables when the user starts a graphi-
          cal session. It is recommended to keep the environment
          blocks in both the system and user managers managers lean.

          Hint: systemd-run -P env and systemd-run --user -P env print
          the effective system and user service environment blocks.

        Environment Variables Set or Propagated by the Service Manager

          The following environment variables are propagated by the
          service manager or generated internally for each invoked
          process:

          $PATH
              Colon-separated list of directories to use when launch-
              ing executables.  systemd uses a fixed value of
              "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin" in
              the system manager. When compiled for systems with
              "unmerged /usr/" (/bin is not a symlink to /usr/bin),
              ":/sbin:/bin" is appended. In case of the the user man-
              ager, a different path may be configured by the distri-
              bution. It is recommended to not rely on the order of
              entries, and have only one program with a given name in
              $PATH.

          $LANG
              Locale. Can be set in locale.conf(5) or on the kernel
              command line (see systemd(1) and kernel-command-
              line(7)).

          $USER, $LOGNAME, $HOME, $SHELL
              User name (twice), home directory, and the login shell.
              The variables are set for the units that have User= set,
              which includes user systemd instances. See passwd(5).

          $INVOCATION_ID

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              Contains a randomized, unique 128bit ID identifying each
              runtime cycle of the unit, formatted as 32 character
              hexadecimal string. A new ID is assigned each time the
              unit changes from an inactive state into an activating
              or active state, and may be used to identify this spe-
              cific runtime cycle, in particular in data stored
              offline, such as the journal. The same ID is passed to
              all processes run as part of the unit.

          $XDG_RUNTIME_DIR
              The directory to use for runtime objects (such as IPC
              objects) and volatile state. Set for all services run by
              the user systemd instance, as well as any system ser-
              vices that use PAMName= with a PAM stack that includes
              pam_systemd. See below and pam_systemd(8) for more
              information.

          $RUNTIME_DIRECTORY, $STATE_DIRECTORY, $CACHE_DIRECTORY,
          $LOGS_DIRECTORY, $CONFIGURATION_DIRECTORY
              Absolute paths to the directories defined with Run-
              timeDirectory=, StateDirectory=, CacheDirectory=, Logs-
              Directory=, and ConfigurationDirectory= when those set-
              tings are used.

          $CREDENTIALS_DIRECTORY
              An absolute path to the per-unit directory with creden-
              tials configured via LoadCredential=/SetCredential=. The
              directory is marked read-only and is placed in unswap-
              pable memory (if supported and permitted), and is only
              accessible to the UID associated with the unit via User=
              or DynamicUser= (and the superuser).

          $MAINPID
              The PID of the unit's main process if it is known. This
              is only set for control processes as invoked by Exe-
              cReload= and similar.

          $MANAGERPID
              The PID of the user systemd instance, set for processes
              spawned by it.

          $LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
              Information about file descriptors passed to a service
              for socket activation. See sd_listen_fds(3).

          $NOTIFY_SOCKET
              The socket sd_notify() talks to. See sd_notify(3).

          $WATCHDOG_PID, $WATCHDOG_USEC
              Information about watchdog keep-alive notifications. See
              sd_watchdog_enabled(3).

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          $TERM
              Terminal type, set only for units connected to a termi-
              nal (StandardInput=tty, StandardOutput=tty, or
              StandardError=tty). See termcap(5).

          $LOG_NAMESPACE
              Contains the name of the selected logging namespace when
              the LogNamespace= service setting is used.

          $JOURNAL_STREAM
              If the standard output or standard error output of the
              executed processes are connected to the journal (for
              example, by setting StandardError=journal)
              $JOURNAL_STREAM contains the device and inode numbers of
              the connection file descriptor, formatted in decimal,
              separated by a colon (":"). This permits invoked pro-
              cesses to safely detect whether their standard output or
              standard error output are connected to the journal. The
              device and inode numbers of the file descriptors should
              be compared with the values set in the environment vari-
              able to determine whether the process output is still
              connected to the journal. Note that it is generally not
              sufficient to only check whether $JOURNAL_STREAM is set
              at all as services might invoke external processes
              replacing their standard output or standard error out-
              put, without unsetting the environment variable.

              If both standard output and standard error of the exe-
              cuted processes are connected to the journal via a
              stream socket, this environment variable will contain
              information about the standard error stream, as that's
              usually the preferred destination for log data. (Note
              that typically the same stream is used for both standard
              output and standard error, hence very likely the envi-
              ronment variable contains device and inode information
              matching both stream file descriptors.)

              This environment variable is primarily useful to allow
              services to optionally upgrade their used log protocol
              to the native journal protocol (using
              sd_journal_print(3) and other functions) if their stan-
              dard output or standard error output is connected to the
              journal anyway, thus enabling delivery of structured
              metadata along with logged messages.

          $SERVICE_RESULT
              Only defined for the service unit type, this environment
              variable is passed to all ExecStop= and ExecStopPost=
              processes, and encodes the service "result". Currently,
              the following values are defined:

              Table 5. Defined $SERVICE_RESULT values allbox tab(:);

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              lB lB.  T{ Value T}:T{ Meaning T} l l l l l l l l l l l
              l l l l l l l.  T{ "success" T}:T{ The service ran suc-
              cessfully and exited cleanly.  T} T{ "protocol" T}:T{ A
              protocol violation occurred: the service did not take
              the steps required by its unit configuration (specifi-
              cally what is configured in its Type= setting).  T} T{
              "timeout" T}:T{ One of the steps timed out.  T} T{
              "exit-code" T}:T{ Service process exited with a non-zero
              exit code; see $EXIT_CODE below for the actual exit code
              returned.  T} T{ "signal" T}:T{ A service process was
              terminated abnormally by a signal, without dumping core.
              See $EXIT_CODE below for the actual signal causing the
              termination.  T} T{ "core-dump" T}:T{ A service process
              terminated abnormally with a signal and dumped core. See
              $EXIT_CODE below for the signal causing the termination.
              T} T{ "watchdog" T}:T{ Watchdog keep-alive ping was
              enabled for the service, but the deadline was missed.
              T} T{ "start-limit-hit" T}:T{ A start limit was defined
              for the unit and it was hit, causing the unit to fail to
              start. See systemd.unit(5)'s StartLimitIntervalSec= and
              StartLimitBurst= for details.  T} T{ "resources" T}:T{ A
              catch-all condition in case a system operation failed.
              T}

              This environment variable is useful to monitor failure
              or successful termination of a service. Even though this
              variable is available in both ExecStop= and ExecStop-
              Post=, it is usually a better choice to place monitoring
              tools in the latter, as the former is only invoked for
              services that managed to start up correctly, and the
              latter covers both services that failed during their
              start-up and those which failed during their runtime.

          $EXIT_CODE, $EXIT_STATUS
              Only defined for the service unit type, these environ-
              ment variables are passed to all ExecStop=, ExecStop-
              Post= processes and contain exit status/code information
              of the main process of the service. For the precise def-
              inition of the exit code and status, see wait(2).
              $EXIT_CODE is one of "exited", "killed", "dumped".
              $EXIT_STATUS contains the numeric exit code formatted as
              string if $EXIT_CODE is "exited", and the signal name in
              all other cases. Note that these environment variables
              are only set if the service manager succeeded to start
              and identify the main process of the service.

              Table 6. Summary of possible service result variable
              allbox tab(:); lB lB lB.  T{ $SERVICE_RESULT T}:T{
              $EXIT_CODE T}:T{ $EXIT_STATUS T} lt lt l ^ lt l lt lt l
              ^ l l lt lt l ^ lt l lt lt l lt lt l lt lt l lt l l ^ l
              l ^ l l lt l l lt lt l l l l l l l l s s.  T{ "success"
              T}:T{ "killed" T}:T{ "HUP", "INT", "TERM", "PIPE" T} :T{

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

              "exited" T}:T{ "0" T} T{ "protocol" T}:T{ not set T}:T{
              not set T} :T{ "exited" T}:T{ "0" T} T{ "timeout" T}:T{
              "killed" T}:T{ "TERM", "KILL" T} :T{ "exited" T}:T{ "0",
              "1", "2", "3", ..., "255" T} T{ "exit-code" T}:T{
              "exited" T}:T{ "1", "2", "3", ..., "255" T} T{ "signal"
              T}:T{ "killed" T}:T{ "HUP", "INT", "KILL", ...  T} T{
              "core-dump" T}:T{ "dumped" T}:T{ "ABRT", "SEGV", "QUIT",
              ...  T} T{ "watchdog" T}:T{ "dumped" T}:T{ "ABRT" T} :T{
              "killed" T}:T{ "TERM", "KILL" T} :T{ "exited" T}:T{ "0",
              "1", "2", "3", ..., "255" T} T{ "exec-condition" T}:T{
              "exited" T}:T{ "1", "2", "3", "4", ..., "254" T} T{
              "oom-kill" T}:T{ "killed" T}:T{ "TERM", "KILL" T} T{
              "start-limit-hit" T}:T{ not set T}:T{ not set T} T{
              "resources" T}:T{ any of the above T}:T{ any of the
              above T} T{ Note: the process may be also terminated by
              a signal not sent by systemd. In particular the process
              may send an arbitrary signal to itself in a handler for
              any of the non-maskable signals. Nevertheless, in the
              "timeout" and "watchdog" rows above only the signals
              that systemd sends have been included. Moreover, using
              SuccessExitStatus= additional exit statuses may be
              declared to indicate clean termination, which is not
              reflected by this table.  T}

          $PIDFILE
              The path to the configured PID file, in case the process
              is forked off on behalf of a service that uses the PID-
              File= setting, see systemd.service(5) for details. Ser-
              vice code may use this environment variable to automati-
              cally generate a PID file at the location configured in
              the unit file. This field is set to an absolute path in
              the file system.

          For system services, when PAMName= is enabled and
          pam_systemd is part of the selected PAM stack, additional
          environment variables defined by systemd may be set for ser-
          vices. Specifically, these are $XDG_SEAT, $XDG_VTNR, see
          pam_systemd(8) for details.

     PROCESS EXIT CODES
          When invoking a unit process the service manager possibly
          fails to apply the execution parameters configured with the
          settings above. In that case the already created service
          process will exit with a non-zero exit code before the con-
          figured command line is executed. (Or in other words, the
          child process possibly exits with these error codes, after
          having been created by the fork(2) system call, but before
          the matching execve(2) system call is called.) Specifically,
          exit codes defined by the C library, by the LSB specifica-
          tion and by the systemd service manager itself are used.

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

          The following basic service exit codes are defined by the C
          library.

          Table 7. Basic C library exit codes allbox tab(:); lB lB lB.
          T{ Exit Code T}:T{ Symbolic Name T}:T{ Description T} l l l
          l l l.  T{ 0 T}:T{ EXIT_SUCCESS T}:T{ Generic success code.
          T} T{ 1 T}:T{ EXIT_FAILURE T}:T{ Generic failure or unspeci-
          fied error.  T}

          The following service exit codes are defined by the
          m[blue]LSB specificationm[][10].

          Table 8. LSB service exit codes allbox tab(:); lB lB lB.  T{
          Exit Code T}:T{ Symbolic Name T}:T{ Description T} l l l l l
          l l l l l l l l l l l l l.  T{ 2 T}:T{ EXIT_INVALIDARGUMENT
          T}:T{ Invalid or excess arguments.  T} T{ 3 T}:T{
          EXIT_NOTIMPLEMENTED T}:T{ Unimplemented feature.  T} T{ 4
          T}:T{ EXIT_NOPERMISSION T}:T{ The user has insufficient
          privileges.  T} T{ 5 T}:T{ EXIT_NOTINSTALLED T}:T{ The pro-
          gram is not installed.  T} T{ 6 T}:T{ EXIT_NOTCONFIGURED
          T}:T{ The program is not configured.  T} T{ 7 T}:T{
          EXIT_NOTRUNNING T}:T{ The program is not running.  T}

          The LSB specification suggests that error codes 200 and
          above are reserved for implementations. Some of them are
          used by the service manager to indicate problems during pro-
          cess invocation:

          Table 9. systemd-specific exit codes allbox tab(:); lB lB
          lB.  T{ Exit Code T}:T{ Symbolic Name T}:T{ Description T} l
          l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l
          l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l
          l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l
          l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l
          l l l l l.  T{ 200 T}:T{ EXIT_CHDIR T}:T{ Changing to the
          requested working directory failed. See WorkingDirectory=
          above.  T} T{ 201 T}:T{ EXIT_NICE T}:T{ Failed to set up
          process scheduling priority (nice level). See Nice= above.
          T} T{ 202 T}:T{ EXIT_FDS T}:T{ Failed to close unwanted file
          descriptors, or to adjust passed file descriptors.  T} T{
          203 T}:T{ EXIT_EXEC T}:T{ The actual process execution
          failed (specifically, the execve(2) system call). Most
          likely this is caused by a missing or non-accessible exe-
          cutable file.  T} T{ 204 T}:T{ EXIT_MEMORY T}:T{ Failed to
          perform an action due to memory shortage.  T} T{ 205 T}:T{
          EXIT_LIMITS T}:T{ Failed to adjust resource limits. See Lim-
          itCPU= and related settings above.  T} T{ 206 T}:T{
          EXIT_OOM_ADJUST T}:T{ Failed to adjust the OOM setting. See
          OOMScoreAdjust= above.  T} T{ 207 T}:T{ EXIT_SIGNAL_MASK
          T}:T{ Failed to set process signal mask.  T} T{ 208 T}:T{

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

          EXIT_STDIN T}:T{ Failed to set up standard input. See Stan-
          dardInput= above.  T} T{ 209 T}:T{ EXIT_STDOUT T}:T{ Failed
          to set up standard output. See StandardOutput= above.  T} T{
          210 T}:T{ EXIT_CHROOT T}:T{ Failed to change root directory
          (chroot(2)). See RootDirectory=/RootImage= above.  T} T{ 211
          T}:T{ EXIT_IOPRIO T}:T{ Failed to set up IO scheduling pri-
          ority. See IOSchedulingClass=/IOSchedulingPriority= above.
          T} T{ 212 T}:T{ EXIT_TIMERSLACK T}:T{ Failed to set up timer
          slack. See TimerSlackNSec= above.  T} T{ 213 T}:T{
          EXIT_SECUREBITS T}:T{ Failed to set process secure bits. See
          SecureBits= above.  T} T{ 214 T}:T{ EXIT_SETSCHEDULER T}:T{
          Failed to set up CPU scheduling. See
          CPUSchedulingPolicy=/CPUSchedulingPriority= above.  T} T{
          215 T}:T{ EXIT_CPUAFFINITY T}:T{ Failed to set up CPU affin-
          ity. See CPUAffinity= above.  T} T{ 216 T}:T{ EXIT_GROUP
          T}:T{ Failed to determine or change group credentials. See
          Group=/SupplementaryGroups= above.  T} T{ 217 T}:T{
          EXIT_USER T}:T{ Failed to determine or change user creden-
          tials, or to set up user namespacing. See
          User=/PrivateUsers= above.  T} T{ 218 T}:T{
          EXIT_CAPABILITIES T}:T{ Failed to drop capabilities, or
          apply ambient capabilities. See
          CapabilityBoundingSet=/AmbientCapabilities= above.  T} T{
          219 T}:T{ EXIT_CGROUP T}:T{ Setting up the service control
          group failed.  T} T{ 220 T}:T{ EXIT_SETSID T}:T{ Failed to
          create new process session.  T} T{ 221 T}:T{ EXIT_CONFIRM
          T}:T{ Execution has been cancelled by the user. See the
          systemd.confirm_spawn= kernel command line setting on
          kernel-command-line(7) for details.  T} T{ 222 T}:T{
          EXIT_STDERR T}:T{ Failed to set up standard error output.
          See StandardError= above.  T} T{ 224 T}:T{ EXIT_PAM T}:T{
          Failed to set up PAM session. See PAMName= above.  T} T{ 225
          T}:T{ EXIT_NETWORK T}:T{ Failed to set up network namespac-
          ing. See PrivateNetwork= above.  T} T{ 226 T}:T{
          EXIT_NAMESPACE T}:T{ Failed to set up mount namespacing. See
          ReadOnlyPaths= and related settings above.  T} T{ 227 T}:T{
          EXIT_NO_NEW_PRIVILEGES T}:T{ Failed to disable new privi-
          leges. See NoNewPrivileges=yes above.  T} T{ 228 T}:T{
          EXIT_SECCOMP T}:T{ Failed to apply system call filters. See
          SystemCallFilter= and related settings above.  T} T{ 229
          T}:T{ EXIT_SELINUX_CONTEXT T}:T{ Determining or changing
          SELinux context failed. See SELinuxContext= above.  T} T{
          230 T}:T{ EXIT_PERSONALITY T}:T{ Failed to set up an execu-
          tion domain (personality). See Personality= above.  T} T{
          231 T}:T{ EXIT_APPARMOR_PROFILE T}:T{ Failed to prepare
          changing AppArmor profile. See AppArmorProfile= above.  T}
          T{ 232 T}:T{ EXIT_ADDRESS_FAMILIES T}:T{ Failed to restrict
          address families. See RestrictAddressFamilies= above.  T} T{
          233 T}:T{ EXIT_RUNTIME_DIRECTORY T}:T{ Setting up runtime
          directory failed. See RuntimeDirectory= and related settings
          above.  T} T{ 235 T}:T{ EXIT_CHOWN T}:T{ Failed to adjust
          socket ownership. Used for socket units only.  T} T{ 236

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     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

          T}:T{ EXIT_SMACK_PROCESS_LABEL T}:T{ Failed to set SMACK
          label. See SmackProcessLabel= above.  T} T{ 237 T}:T{
          EXIT_KEYRING T}:T{ Failed to set up kernel keyring.  T} T{
          238 T}:T{ EXIT_STATE_DIRECTORY T}:T{ Failed to set up unit's
          state directory. See StateDirectory= above.  T} T{ 239 T}:T{
          EXIT_CACHE_DIRECTORY T}:T{ Failed to set up unit's cache
          directory. See CacheDirectory= above.  T} T{ 240 T}:T{
          EXIT_LOGS_DIRECTORY T}:T{ Failed to set up unit's logging
          directory. See LogsDirectory= above.  T} T{ 241 T}:T{
          EXIT_CONFIGURATION_DIRECTORY T}:T{ Failed to set up unit's
          configuration directory. See ConfigurationDirectory= above.
          T} T{ 242 T}:T{ EXIT_NUMA_POLICY T}:T{ Failed to set up
          unit's NUMA memory policy. See NUMAPolicy= and NUMAMask=
          above.  T} T{ 243 T}:T{ EXIT_CREDENTIALS T}:T{ Failed to set
          up unit's credentials. See LoadCredential= and SetCreden-
          tial= above.  T}

          Finally, the BSD operating systems define a set of exit
          codes, typically defined on Linux systems too:

          Table 10. BSD exit codes allbox tab(:); lB lB lB.  T{ Exit
          Code T}:T{ Symbolic Name T}:T{ Description T} l l l l l l l
          l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l
          l l l l l l l l.  T{ 64 T}:T{ EX_USAGE T}:T{ Command line
          usage error T} T{ 65 T}:T{ EX_DATAERR T}:T{ Data format
          error T} T{ 66 T}:T{ EX_NOINPUT T}:T{ Cannot open input T}
          T{ 67 T}:T{ EX_NOUSER T}:T{ Addressee unknown T} T{ 68 T}:T{
          EX_NOHOST T}:T{ Host name unknown T} T{ 69 T}:T{
          EX_UNAVAILABLE T}:T{ Service unavailable T} T{ 70 T}:T{
          EX_SOFTWARE T}:T{ internal software error T} T{ 71 T}:T{
          EX_OSERR T}:T{ System error (e.g., can't fork) T} T{ 72
          T}:T{ EX_OSFILE T}:T{ Critical OS file missing T} T{ 73
          T}:T{ EX_CANTCREAT T}:T{ Can't create (user) output file T}
          T{ 74 T}:T{ EX_IOERR T}:T{ Input/output error T} T{ 75 T}:T{
          EX_TEMPFAIL T}:T{ Temporary failure; user is invited to
          retry T} T{ 76 T}:T{ EX_PROTOCOL T}:T{ Remote error in pro-
          tocol T} T{ 77 T}:T{ EX_NOPERM T}:T{ Permission denied T} T{
          78 T}:T{ EX_CONFIG T}:T{ Configuration error T}

     SEE ALSO
          systemd(1), systemctl(1), systemd-analyze(1), journalctl(1),
          systemd-system.conf(5), systemd.unit(5), systemd.service(5),
          systemd.socket(5), systemd.swap(5), systemd.mount(5),
          systemd.kill(5), systemd.resource-control(5),
          systemd.time(7), systemd.directives(7), tmpfiles.d(5),
          exec(3), fork(2)

     NOTES
           1. Discoverable Partitions Specification
              https://systemd.io/DISCOVERABLE_PARTITIONS

     Page 63                    systemd 247          (printed 5/26/22)

     SYSTEMD.EXEC(5)                                   SYSTEMD.EXEC(5)

           2. The /proc Filesystem
              https://www.kernel.org/doc/html/latest/filesystems/proc.html#mount-options

           3. User/Group Name Syntax
              https://systemd.io/USER_NAMES

           4. No New Privileges Flag
              https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html

           5. JSON User Record
              https://systemd.io/USER_RECORD

           6. proc.txt
              https://www.kernel.org/doc/Documentation/filesystems/proc.txt

           7. C escapes
              https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences

           8. most control characters
              https://en.wikipedia.org/wiki/Control_character#In_ASCII

           9. Base64
              https://tools.ietf.org/html/rfc2045#section-6.8

          10. LSB specification
              https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html

     Page 64                    systemd 247          (printed 5/26/22)