6.15. pam_limits - limit resources

pam_limits.so [ change_uid ] [ conf=/path/to/limits.conf ] [ debug ] [ utmp_early ] [ noaudit ]

6.15.1. DESCRIPTION

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 /etc/security/limits.conf config file. Then individual files from the /etc/security/limits.d/ 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 explicitely 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.

6.15.2. DESCRIPTION

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.

<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 files

rss

maximum resident set size (KB)

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 except for this with uid=0

maxsyslogins

maximum number of logins on system

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)

msqqueue

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)

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.

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

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

6.15.3. OPTIONS

change_uid

Change real uid to the user for who the limits are set up. Use this option if you have problems like login not forking a shell for user who has no processes. Be warned that something else may break when you do this.

conf=/path/to/limits.conf

Indicate an alternative limits.conf style configuration file to override the default.

debug

Print debug information.

utmp_early

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.

noaudit

Do not report exceeded maximum logins count to the audit subsystem.

6.15.4. MODULE SERVICES PROVIDED

Only the session service is supported.

6.15.5. RETURN VALUES

PAM_ABORT

Cannot get current limits.

PAM_IGNORE

No limits found for this user.

PAM_PERM_DENIED

New limits could not be set.

PAM_SERVICE_ERR

Cannot read config file.

PAM_SESSEION_ERR

Error recovering account name.

PAM_SUCCESS

Limits were changed.

PAM_USER_UNKNOWN

The user is not known to the system.

6.15.6. FILES

/etc/security/limits.conf

Default configuration file

6.15.7. EXAMPLES

These are some example lines which might be specified in /etc/security/limits.conf.

*               soft    core            0
*               hard    rss             10000
@student        hard    nproc           20
@faculty        soft    nproc           20
@faculty        hard    nproc           50
ftp             hard    nproc           0
@student        -       maxlogins       4
    

6.15.8. AUTHORS

pam_limits was initially written by Cristian Gafton <gafton@redhat.com>