6.16. pam_limits - limit resources
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## 6.16. pam_limits - limit resources

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

### 6.16.1. 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 *.conf 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 explicitly specified with a module option then the files in the above directory are not parsed.

By default limits are taken from the `/etc/security/limits.conf` config file or, if that one is not present, the file `%vendordir%/security/limits.conf`. Then individual `*.conf` files from the `/etc/security/limits.d/` and `%vendordir%/security/limits.d` directories are read. If `/etc/security/limits.d/@filename@.conf` exists, then `%vendordir%/security/limits.d/@filename@.conf` will not be used. All `limits.d/*.conf` files are sorted by their `@filename@.conf` in lexicographic order regardless of which of the directories they reside in. 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 the `config` option the files in the above directories 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.

### 6.16.2. 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>

  - 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.

  NOTE: group and wildcard limits are not applied to the root user. To set a limit for the root user, this field must contain the literal username root.

<type>
  hard

    for enforcing hard resource limits. These limits are set by the superuser and enforced by the Kernel. Users cannot raise their own 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)

  `chroot`

    the directory to chroot the user to

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).

### 6.16.3. OPTIONS

conf=/path/to/limits.conf

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

debug

  Print debug information.

set_all

  Set the limits for which no value is specified in the configuration file to the one from the process with the PID 1. Please note that if the init process is systemd these limits will not be the kernel default limits and this option should not be used.

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.

### 6.16.4. MODULE TYPES PROVIDED

Only the `session` module type is provided.

### 6.16.5. 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_SESSION_ERR

  Error recovering account name.

PAM_SUCCESS

  Limits were changed.

PAM_USER_UNKNOWN

  The user is not known to the system.

### 6.16.6. FILES

/etc/security/limits.conf

  Default configuration file

%vendordir%/security/limits.conf

  Default configuration file if `/etc/security/limits.conf` does not exist.

### 6.16.7. EXAMPLES

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

    *               soft    core            0
    root            hard    core            100000
    *               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

### 6.16.8. AUTHORS

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

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