Linux set user limit

If your application is giving error like below, or you want to increase user limit of open files, user limit of max processes follow this post.

System Requirement: max file descriptors [4096] likely too low, increase to at least [65536].

To see the current limit of the maximum number of processes for the oracle user, run:

ulimit –aH à to check Hard limits (-a display all limit)

ulimit -aS   à  to check Soft limit

ulimit –nH   à Check hard limit of max open file (use -u for max user processes)

ulimit –nS   à Check Soft limit of max open file

Example:

ulimit -Hn 4096

[aadmin@host1 opt]$ 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) 128540

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) 4096

virtual memory          (kbytes, -v) unlimited

file locks                      (-x) unlimited

The above value can be low for some application, you can change these value like below:

su - myuser

sudo vi /etc/security/limits.conf

<domain>        <type>  <item>  <value>

myuser                 -       nproc           65536

myuser                 -       nofile          63536

--- restart the server

Here:

nofile - max number of open files

nproc - max number of processes

Alternatively to make this change permanent, you could add "ulimit -u 65536" for nproc and "ulimit -n 63536" for nofile, to the ~oracle/.bash_profile file which is the user start up file for the bash shell on RHEL.

Verification:

aadmin@host1:~$ 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) 128595

max locked memory       (kbytes, -l) 64

max memory size         (kbytes, -m) unlimited

open files                      (-n) 10240

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) 10240

virtual memory          (kbytes, -v) unlimited

file locks                      (-x) unlimited

Note the user above is aadmin and changes is done for myuser user.

[root@host1 aadmin]# su - myuser -c 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) 128540

max locked memory       (kbytes, -l) 64

max memory size         (kbytes, -m) unlimited

open files                      (-n) 63536

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) 65536

virtual memory          (kbytes, -v) unlimited

file locks                      (-x) unlimited

NOTE: It is not recommend to set the "hard" limit for nofile for the oracle user equal to /proc/sys/fs/file-max. If you do that and the user uses up all the file handles, then the entire system will run out of file handles. That is why the hard limit should be set to 63536 and not 65536.