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>
• a username
• a groupname, with @group syntax. This should not be
confused with netgroups.
• the wildcard *, for default entry.
• 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.
• 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.
• 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.
• 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 user 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 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 ignored.
The pam_limits module does report configuration problems found in
its configuration file and errors via syslog(3).
