The pam_limits PAM module sets limits on the system resources that can be obtained in a user-session. Users of uid=0 are affected by this limits, too.
By default limits are taken from the
config file. Then individual *.conf files from the
directory are read. The files are parsed one after another in the order of "C" locale.
The effect of the individual files is the same as if all the files were
concatenated together in the order of parsing.
If a config file is explicitly specified with a module option then the
files in the above directory are not parsed.
The module must not be called by a multithreaded application.
If Linux PAM is compiled with audit support the module will report when it denies access based on limit of maximum number of concurrent login sessions.
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
The syntax of the lines is as follows:
The fields listed above should be filled as follows:
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
<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 @
<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 %:
to maxlogins limit only. It limits the total number of logins of all users
that are member of the group with the specified gid.
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 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. .
limits the core file size (KB)
maximum data size (KB)
maximum filesize (KB)
maximum locked-in-memory address space (KB)
maximum number of open files
maximum resident set size (KB) (Ignored in Linux 2.4.30 and higher)
maximum stack size (KB)
maximum CPU time (minutes)
maximum number of processes
address space limit (KB)
maximum number of logins for this user except for this with uid=0
maximum number of all logins on system
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 higher)
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)
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).
Indicate an alternative limits.conf style configuration file to override the default.
Print debug information.
Set the limits for which no value is specified in the configuration file to the one from the process with the PID 1.
Some broken applications actually allocate a utmp entry for the user before the user is admitted to the system. If some of the services you are configuring PAM for do this, you can selectively use this module argument to compensate for this behavior and at the same time maintain system-wide consistency with a single limits.conf file.
Do not report exceeded maximum logins count to the audit subsystem.
Cannot get current limits.
No limits found for this user.
New limits could not be set.
Cannot read config file.
Error recovering account name.
Limits were changed.
The user is not known to the system.
These are some example lines which might be specified in
* 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