Imposing user limits on login.
THEORY OF OPERATION:
First, make a root-only-readable file (/etc/security/limits.conf by
default or INSTALLED_CONFILE defined Makefile) that describes the
resource limits you wish to impose. No priority changes and login
limit checks are done on UID 0 accounts.
Each line describes a limit for a user in the form:
<domain> <type> <item> <value>
<domain> can be:
- an user name
- a group name, with @group syntax
- the wildcard *, for default entry
<type> can have the three values:
- "soft" for enforcing the soft limits
- "hard" for enforcing hard limits
- "-" for enforcing both soft and hard limits
<item> can be one of the following:
- core - limits the core file size (KB)
- data - max data size (KB)
- fsize - maximum filesize (KB)
- memlock - max locked-in-memory address space (KB)
- nofile - max number of open files
- rss - max resident set size (KB)
- stack - max stack size (KB)
- cpu - max CPU time (MIN)
- nproc - max number of processes
- as - address space limit
- maxlogins - max number of logins for this user
- maxsyslogins - max number of logins on the system
- priority - lower the priority by given value (value can be -ve)
- locks - max locked files (Linux 2.4 and higher)
- sigpending - max number of pending signals (Linux 2.6 and higher)
- msgqueue - max memory used by POSIX message queues (bytes)
(Linux 2.6 and higher)
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. .
Please remember that individual limits have priority over group
limits, so if you impose no limits for admin group, but one of the
members in this group has 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 (they apply for the session only).
In the LIMITS_FILE, the # character introduces a comment - the rest of the
line is ignored.
The pam_limits module does its best to report configuration problems found
in LIMITS_FILE via syslog.
EXAMPLE configuration file:
* 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
debug verbose logging
conf=/path/to/file the limits configuration file if different from the
one set at compile time.
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.
utmp_early some broken applications actually allocate a
utmp entry for the user before the user is
admitted to the system. If the service you are
configuring PAM for does this, you can use
this module argument to compensate for this
MODULE SERVICES PROVIDED:
session _open_session and _close_session (blank)
For the services you need resources limits (login for example) put a
the following line in /etc/pam.conf as the last line for that
service (usually after the pam_unix session line:
login session required /lib/security/pam_limits.so
Replace "login" for each service you are using this module, replace
"/lib/security" path with your real modules path.
Cristian Gafton <email@example.com>
Thanks to Elliot Lee <firstname.lastname@example.org> for his comments on
improving this module, and Jens Sorensen for Linux 2.4 updates.