SYSTEMD.JOURNAL-FIELDS(7)               SYSTEMD.JOURNAL-FIELDS(7)

     NAME
          systemd.journal-fields - Special journal fields

     DESCRIPTION
          Entries in the journal (as written by systemd-
          journald.service(8)) resemble a UNIX process environment
          block in syntax but with fields that may include binary
          data. Primarily, fields are formatted UTF-8 text strings,
          and binary encoding is used only where formatting as UTF-8
          text strings makes little sense. New fields may freely be
          defined by applications, but a few fields have special
          meanings. All fields with special meanings are optional. In
          some cases, fields may appear more than once per entry.

     USER JOURNAL FIELDS
          User fields are fields that are directly passed from clients
          and stored in the journal.

          MESSAGE=
              The human-readable message string for this entry. This
              is supposed to be the primary text shown to the user. It
              is usually not translated (but might be in some cases),
              and is not supposed to be parsed for metadata.

          MESSAGE_ID=
              A 128-bit message identifier ID for recognizing certain
              message types, if this is desirable. This should contain
              a 128-bit ID formatted as a lower-case hexadecimal
              string, without any separating dashes or suchlike. This
              is recommended to be a UUID-compatible ID, but this is
              not enforced, and formatted differently. Developers can
              generate a new ID for this purpose with systemd-id128
              new.

          PRIORITY=
              A priority value between 0 ("emerg") and 7 ("debug")
              formatted as a decimal string. This field is compatible
              with syslog's priority concept.

          CODE_FILE=, CODE_LINE=, CODE_FUNC=
              The code location generating this message, if known.
              Contains the source filename, the line number and the
              function name.

          ERRNO=
              The low-level Unix error number causing this entry, if
              any. Contains the numeric value of errno(3) formatted as
              a decimal string.

          INVOCATION_ID=, USER_INVOCATION_ID=

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              A randomized, unique 128-bit ID identifying each runtime
              cycle of the unit. This is different from
              _SYSTEMD_INVOCATION_ID in that it is only used for
              messages coming from systemd code (e.g. logs from the
              system/user manager or from forked processes performing
              systemd-related setup).

          SYSLOG_FACILITY=, SYSLOG_IDENTIFIER=, SYSLOG_PID=,
          SYSLOG_TIMESTAMP=
              Syslog compatibility fields containing the facility
              (formatted as decimal string), the identifier string
              (i.e. "tag"), the client PID, and the timestamp as
              specified in the original datagram. (Note that the tag
              is usually derived from glibc's
              program_invocation_short_name variable, see
              program_invocation_short_name(3).)

              Note that the journal service does not validate the
              values of any structured journal fields whose name is
              not prefixed with an underscore, and this includes any
              syslog related fields such as these. Hence, applications
              that supply a facility, PID, or log level are expected
              to do so properly formatted, i.e. as numeric integers
              formatted as decimal strings.

          SYSLOG_RAW=
              The original contents of the syslog line as received in
              the syslog datagram. This field is only included if the
              MESSAGE= field was modified compared to the original
              payload or the timestamp could not be located properly
              and is not included in SYSLOG_TIMESTAMP=. Message
              truncation occurs when when the message contains leading
              or trailing whitespace (trailing and leading whitespace
              is stripped), or it contains an embedded NUL byte (the
              NUL byte and anything after it is not included). Thus,
              the original syslog line is either stored as SYSLOG_RAW=
              or it can be recreated based on the stored priority and
              facility, timestamp, identifier, and the message payload
              in MESSAGE=.

          DOCUMENTATION=
              A documentation URL with further information about the
              topic of the log message. Tools such as journalctl will
              include a hyperlink to an URL specified this way in
              their output. Should be a "http://", "https://",
              "file:/", "man:" or "info:" URL.

          TID=
              The numeric thread ID (TID) the log message originates
              from.

     TRUSTED JOURNAL FIELDS

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          Fields prefixed with an underscore are trusted fields, i.e.
          fields that are implicitly added by the journal and cannot
          be altered by client code.

          _PID=, _UID=, _GID=
              The process, user, and group ID of the process the
              journal entry originates from formatted as a decimal
              string. Note that entries obtained via "stdout" or
              "stderr" of forked processes will contain credentials
              valid for a parent process (that initiated the
              connection to systemd-journald).

          _COMM=, _EXE=, _CMDLINE=
              The name, the executable path, and the command line of
              the process the journal entry originates from.

          _CAP_EFFECTIVE=
              The effective capabilities(7) of the process the journal
              entry originates from.

          _AUDIT_SESSION=, _AUDIT_LOGINUID=
              The session and login UID of the process the journal
              entry originates from, as maintained by the kernel audit
              subsystem.

          _SYSTEMD_CGROUP=, _SYSTEMD_SLICE=, _SYSTEMD_UNIT=,
          _SYSTEMD_USER_UNIT=, _SYSTEMD_USER_SLICE=,
          _SYSTEMD_SESSION=, _SYSTEMD_OWNER_UID=
              The control group path in the systemd hierarchy, the
              systemd slice unit name, the systemd unit name, the unit
              name in the systemd user manager (if any), the systemd
              session ID (if any), and the owner UID of the systemd
              user unit or systemd session (if any) of the process the
              journal entry originates from.

          _SELINUX_CONTEXT=
              The SELinux security context (label) of the process the
              journal entry originates from.

          _SOURCE_REALTIME_TIMESTAMP=
              The earliest trusted timestamp of the message, if any is
              known that is different from the reception time of the
              journal. This is the time in microseconds since the
              epoch UTC, formatted as a decimal string.

          _BOOT_ID=
              The kernel boot ID for the boot the message was
              generated in, formatted as a 128-bit hexadecimal string.

          _MACHINE_ID=
              The machine ID of the originating host, as available in
              machine-id(5).

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          _SYSTEMD_INVOCATION_ID=
              The invocation ID for the runtime cycle of the unit the
              message was generated in, as available to processes of
              the unit in $INVOCATION_ID (see systemd.exec(5)).

          _HOSTNAME=
              The name of the originating host.

          _TRANSPORT=
              How the entry was received by the journal service. Valid
              transports are:

              audit
                  for those read from the kernel audit subsystem

              driver
                  for internally generated messages

              syslog
                  for those received via the local syslog socket with
                  the syslog protocol

              journal
                  for those received via the native journal protocol

              stdout
                  for those read from a service's standard output or
                  error output

              kernel
                  for those read from the kernel

          _STREAM_ID=
              Only applies to "_TRANSPORT=stdout" records: specifies a
              randomized 128bit ID assigned to the stream connection
              when it was first created. This ID is useful to
              reconstruct individual log streams from the log records:
              all log records carrying the same stream ID originate
              from the same stream.

          _LINE_BREAK=
              Only applies to "_TRANSPORT=stdout" records: indicates
              that the log message in the standard output/error stream
              was not terminated with a normal newline character
              ("\n", i.e. ASCII 10). Specifically, when set this field
              is one of nul (in case the line was terminated by a NUL
              byte), line-max (in case the maximum log line length was
              reached, as configured with LineMax= in
              journald.conf(5)), eof (if this was the last log record
              of a stream and the stream ended without a final newline
              character), or pid-change (if the process which
              generated the log output changed in the middle of a

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              line). Note that this record is not generated when a
              normal newline character was used for marking the log
              line end.

          _NAMESPACE=
              If this file was written by a systemd-journald instance
              managing a journal namespace that is not the default,
              this field contains the namespace identifier. See
              systemd-journald.service(8) for details about journal
              namespaces.

     KERNEL JOURNAL FIELDS
          Kernel fields are fields that are used by messages
          originating in the kernel and stored in the journal.

          _KERNEL_DEVICE=
              The kernel device name. If the entry is associated to a
              block device, contains the major and minor numbers of
              the device node, separated by ":" and prefixed by "b".
              Similarly for character devices, but prefixed by "c".
              For network devices, this is the interface index
              prefixed by "n". For all other devices, this is the
              subsystem name prefixed by "+", followed by ":",
              followed by the kernel device name.

          _KERNEL_SUBSYSTEM=
              The kernel subsystem name.

          _UDEV_SYSNAME=
              The kernel device name as it shows up in the device tree
              below /sys/.

          _UDEV_DEVNODE=
              The device node path of this device in /dev/.

          _UDEV_DEVLINK=
              Additional symlink names pointing to the device node in
              /dev/. This field is frequently set more than once per
              entry.

     FIELDS TO LOG ON BEHALF OF A DIFFERENT PROGRAM
          Fields in this section are used by programs to specify that
          they are logging on behalf of another program or unit.

          Fields used by the systemd-coredump coredump kernel helper:

          COREDUMP_UNIT=, COREDUMP_USER_UNIT=
              Used to annotate messages containing coredumps from
              system and session units. See coredumpctl(1).

          Privileged programs (currently UID 0) may attach OBJECT_PID=
          to a message. This will instruct systemd-journald to attach

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          additional fields on behalf of the caller:

          OBJECT_PID=PID
              PID of the program that this message pertains to.

          OBJECT_UID=, OBJECT_GID=, OBJECT_COMM=, OBJECT_EXE=,
          OBJECT_CMDLINE=, OBJECT_AUDIT_SESSION=,
          OBJECT_AUDIT_LOGINUID=, OBJECT_SYSTEMD_CGROUP=,
          OBJECT_SYSTEMD_SESSION=, OBJECT_SYSTEMD_OWNER_UID=,
          OBJECT_SYSTEMD_UNIT=, OBJECT_SYSTEMD_USER_UNIT=
              These are additional fields added automatically by
              systemd-journald. Their meaning is the same as _UID=,
              _GID=, _COMM=, _EXE=, _CMDLINE=, _AUDIT_SESSION=,
              _AUDIT_LOGINUID=, _SYSTEMD_CGROUP=, _SYSTEMD_SESSION=,
              _SYSTEMD_UNIT=, _SYSTEMD_USER_UNIT=, and
              _SYSTEMD_OWNER_UID= as described above, except that the
              process identified by PID is described, instead of the
              process which logged the message.

     ADDRESS FIELDS
          During serialization into external formats, such as the
          m[blue]Journal Export Formatm[][1] or the m[blue]Journal
          JSON Formatm[][2], the addresses of journal entries are
          serialized into fields prefixed with double underscores.
          Note that these are not proper fields when stored in the
          journal but for addressing metadata of entries. They cannot
          be written as part of structured log entries via calls such
          as sd_journal_send(3). They may also not be used as matches
          for sd_journal_add_match(3).

          __CURSOR=
              The cursor for the entry. A cursor is an opaque text
              string that uniquely describes the position of an entry
              in the journal and is portable across machines,
              platforms and journal files.

          __REALTIME_TIMESTAMP=
              The wallclock time (CLOCK_REALTIME) at the point in time
              the entry was received by the journal, in microseconds
              since the epoch UTC, formatted as a decimal string. This
              has different properties from
              "_SOURCE_REALTIME_TIMESTAMP=", as it is usually a bit
              later but more likely to be monotonic.

          __MONOTONIC_TIMESTAMP=
              The monotonic time (CLOCK_MONOTONIC) at the point in
              time the entry was received by the journal in
              microseconds, formatted as a decimal string. To be
              useful as an address for the entry, this should be
              combined with the boot ID in "_BOOT_ID=".

     SEE ALSO

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          systemd(1), systemd-journald.service(8), journalctl(1),
          journald.conf(5), sd-journal(3), coredumpctl(1),
          systemd.directives(7)

     NOTES
           1. Journal Export Format
              https://www.freedesktop.org/wiki/Software/systemd/export

           2. Journal JSON Format
              https://www.freedesktop.org/wiki/Software/systemd/json

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