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LIMITS.CONF(5)                 Linux-PAM Manual                 LIMITS.CONF(5)

NAME
       limits.conf - configuration file for the pam_limits module
DESCRIPTION
       The pam_limits.so 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:
       <domain>
           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.
       <type>
           hard
               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.
           soft
               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 together.
               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. .
       <item>
           core
               limits the core file size (KB)
           data
               maximum data size (KB)
           fsize
               maximum filesize (KB)
           memlock
               maximum locked-in-memory address space (KB)
           nofile
               maximum number of open file descriptors
           rss
               maximum resident set size (KB) (Ignored in Linux 2.4.30 and
               higher)
           stack
               maximum stack size (KB)
           cpu
               maximum CPU time (minutes)
           nproc
               maximum number of processes
           as
               address space limit (KB)
           maxlogins
               maximum number of logins for this user (this limit does not
               apply to user with uid=0)
           maxsyslogins
               maximum number of all logins on system; user is not allowed to
               log-in if total number of all users' logins is greater than
               specified number (this limit does not apply to user with uid=0)
           priority
               the priority to run user process with (negative values boost
               process priority)
           locks
               maximum locked files (Linux 2.4 and higher)
           sigpending
               maximum number of pending signals (Linux 2.6 and higher)
           msgqueue
               maximum memory used by POSIX message queues (bytes) (Linux 2.6
               and higher)
           nice
               maximum nice priority allowed to raise to (Linux 2.6.12 and
               higher) values: [-20,19]
           rtprio
               maximum realtime priority allowed for non-privileged processes
               (Linux 2.6.12 and higher)
       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, the module will reject the login if a limit
       could not be set.
       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 detected 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 ignored.
       The pam_limits module does report configuration problems found in its
       configuration file and errors via syslog(3).
EXAMPLES
       These are some example lines which might be specified in
       /etc/security/limits.conf.
           *               soft    core            0
           *               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

SEE ALSO
       pam_limits(8), pam.d(5), pam(8), getrlimit(2)getrlimit(3p)
AUTHOR
       pam_limits was initially written by Cristian Gafton <gafton AT redhat.com>

Linux-PAM Manual                  04/01/2020                    LIMITS.CONF(5)