DESCRIPTIONTION

The limits file (/etc/limits by default or LIMITS_FILE defined config.h)
describes the resource limits you wish to impose. It should

be owned by root and readable by root account only.

limit file can be found on /etc/limits.

A: max address space (KB)
C: max core file size (KB)
D: max data size (KB)
F: maximum filesize (KB)
M: max locked-in-memory address space (KB)
N: max number of open files
R: max resident set size (KB)
S: max stack size (KB)
T: max CPU time (MIN)
U: max number of processes
K: file creation mask, set by umask(2).
L: max number of logins for this user
P: process priority, set by setpriority(2).

For example, L2D2048N5 is a valid LIMITS_STRING. For reading convenience, the following entries are equivalent:

username L2D2048N5
username L2 D2048 N5

# limits size of any one of users' files" /etc/security/limits.conf
* hard 40000

* = all users
also see ulimit