LIMITS.CONF(5)            (06/08/2020)             LIMITS.CONF(5)

          limits.conf - configuration file for the pam_limits module

          The module applies ulimit limits, nice
          priority and number of simultaneous login sessions limit to
          user login sessions. This description of the configuration
          file syntax applies to the /etc/security/limits.conf file
          and *.conf files in the /etc/security/limits.d directory.

          The syntax of the lines is as follows:

          <domain> <type> <item> <value>

          The fields listed above should be filled as follows:


              +o   a username

              +o   a groupname, with @group syntax. This should not be
                  confused with netgroups.

              +o   the wildcard *, for default entry.

              +o   the wildcard %, for maxlogins limit only, can also
                  be used with %group syntax. If the % wildcard is
                  used alone it is identical to using * with
                  maxsyslogins limit. With a group specified after %
                  it limits the total number of logins of all users
                  that are member of the group.

              +o   an uid range specified as <min_uid>:<max_uid>. If
                  min_uid is omitted, the match is exact for the
                  max_uid. If max_uid is omitted, all uids greater
                  than or equal min_uid match.

              +o   a gid range specified as @<min_gid>:<max_gid>. If
                  min_gid is omitted, the match is exact for the
                  max_gid. If max_gid is omitted, all gids greater
                  than or equal min_gid match. For the exact match all
                  groups including the user's supplementary groups are
                  examined. For the range matches only the user's
                  primary group is examined.

              +o   a gid specified as %:<gid> applicable to maxlogins
                  limit only. It limits the total number of logins of
                  all users that are member of the group with the
                  specified gid.

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              NOTE: group and wildcard limits are not applied to the
              root user. To set a limit for the root user, this field
              must contain the literal username root.


                  for enforcing hard resource limits. These limits are
                  set by the superuser and enforced by the Kernel. The
                  user cannot raise his requirement of system
                  resources above such values.

                  for enforcing soft resource limits. These limits are
                  ones that the user can move up or down within the
                  permitted range by any pre-existing hard limits. The
                  values specified with this token can be thought of
                  as default values, for normal system usage.

                  for enforcing both soft and hard resource limits

                  Note, if you specify a type of '-' but neglect to
                  supply the item and value fields then the module
                  will never enforce any limits on the specified
                  user/group etc. .


                  limits the core file size (KB)

                  maximum data size (KB)

                  maximum filesize (KB)

                  maximum locked-in-memory address space (KB)

                  maximum number of open file descriptors

                  maximum resident set size (KB) (Ignored in Linux
                  2.4.30 and higher)

                  maximum stack size (KB)

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                  maximum CPU time (minutes)

                  maximum number of processes

                  address space limit (KB)

                  maximum number of logins for this user (this limit
                  does not apply to user with uid=0)

                  maximum number of all logins on system; user is not
                  allowed to log-in if total number of all user logins
                  is greater than specified number (this limit does
                  not apply to user with uid=0)

                  the priority to run user process with (negative
                  values boost process priority)

                  maximum locked files (Linux 2.4 and higher)

                  maximum number of pending signals (Linux 2.6 and

                  maximum memory used by POSIX message queues (bytes)
                  (Linux 2.6 and higher)

                  maximum nice priority allowed to raise to (Linux
                  2.6.12 and higher) values: [-20,19]

                  maximum realtime priority allowed for non-privileged
                  processes (Linux 2.6.12 and higher)

                  the directory to chroot the user to

          All items support the values -1, unlimited or infinity
          indicating no limit, except for priority and nice.

          If a hard limit or soft limit of a resource is set to a
          valid value, but outside of the supported range of the local
          system, the system may reject the new limit or unexpected
          behavior may occur. If the control value required is used,

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          the module will reject the login if a limit could not be

          In general, individual limits have priority over group
          limits, so if you impose no limits for admin group, but one
          of the members in this group have a limits line, the user
          will have its limits set according to this line.

          Also, please note that all limit settings are set per login.
          They are not global, nor are they permanent; existing only
          for the duration of the session. One exception is the
          maxlogin option, this one is system wide. But there is a
          race, concurrent logins at the same time will not always be
          detect as such but only counted as one.

          In the limits configuration file, the '#' character
          introduces a comment - after which the rest of the line is

          The pam_limits module does report configuration problems
          found in its configuration file and errors via syslog(3).

          These are some example lines which might be specified in

              *               soft    core            0
              root            hard    core            100000
              *               hard    nofile          512
              @student        hard    nproc           20
              @faculty        soft    nproc           20
              @faculty        hard    nproc           50
              ftp             hard    nproc           0
              @student        -       maxlogins       4
              :123            hard    cpu             5000
              @500:           soft    cpu             10000
              600:700         hard    locks           10

          pam_limits(8), pam.d(5), pam(7), getrlimit(2), getrlimit(3p)

          pam_limits was initially written by Cristian Gafton

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