Most Linux distributions ship with the pam_limits module to limit the resources that can be used by a process. You can enforce process resource limits by the user that a process runs as or by the group name a process runs as. These limits are set in /etc/security/limits.conf. To see the limits for your running shell you can run ulimit with the “-a” option:
$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 63354
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 1024
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
All of the limits above are the system defaults, since I haven’t made any changes to /etc/security/limits.conf. To view the resource limits assigned to an arbitrary process on the system you can page the /proc//limits file. Here are the values assigned to the limits file for my active shell:
$ echo $$
24566
$ cd /proc/24566
$ cat limits
Limit Soft Limit Hard Limit Units
Max cpu time unlimited unlimited seconds
Max file size unlimited unlimited bytes
Max data size unlimited unlimited bytes
Max stack size 8388608 unlimited bytes
Max core file size 0 unlimited bytes
Max resident set unlimited unlimited bytes
Max processes 1024 63354 processes
Max open files 1024 4096 files
Max locked memory 65536 65536 bytes
Max address space unlimited unlimited bytes
Max file locks unlimited unlimited locks
Max pending signals 63354 63354 signals
Max msgqueue size 819200 819200 bytes
Max nice priority 0 0
Max realtime priority 0 0
Max realtime timeout unlimited unlimited us
There are a number of cool things you can do with resource limits, and I’ll type up my resource limits notes and post them in the near future. Rock & roll!