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NAME | DESCRIPTION | EXAMPLES | SEE ALSO | AUTHOR | COLOPHON |
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LIMITS.CONF(5) Linux-PAM Manual LIMITS.CONF(5)
limits.conf - configuration file for the pam_limits module
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)
nonewprivs
value of 0 or 1; if set to 1 disables acquiring new
privileges by invoking prctl(PR_SET_NO_NEW_PRIVS)
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, nice, and nonewprivs. If nofile is
to be set to one of these values, it will be set to the contents
of /proc/sys/fs/nr_open instead (see setrlimit(3)).
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).
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
@student - nonewprivs 1
:123 hard cpu 5000
@500: soft cpu 10000
600:700 hard locks 10
pam_limits(8), pam.d(5), pam(8), getrlimit(2), getrlimit(3p)
pam_limits was initially written by Cristian Gafton
<[email protected]>
This page is part of the linux-pam (Pluggable Authentication
Modules for Linux) project. Information about the project can be
found at ⟨http://www.linux-pam.org/⟩. If you have a bug report
for this manual page, see ⟨//www.linux-pam.org/⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/linux-pam/linux-pam.git⟩ on 2023-12-22. (At
that time, the date of the most recent commit that was found in
the repository was 2023-12-18.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Linux-PAM Manual 12/22/2023 LIMITS.CONF(5)
Pages that refer to this page: htop(1), pam_lastlog(8), pam_limits(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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