Viewing resource limits for Linux processes

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/<pid>/limits file. Here are the values assigned to the limits file for my active shell:

$ echo $$

$ 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!