ulimit command to set & know user limits open files file descriptor max user process etc.

ulimit -n  –> It will display number of open files limit or open file descriptors

ulimit -c –> It display the size of core file

ulimit -u –> It will display the maximum user process limit for the logged in user.

ulimit -f –> It will display the maximum file size that the user can have.

umilit -m –> It will display the maximum memory size for logged in user.

ulimit -v –> It will display the maximum memory size limit

nproc

nofile

root@Ubuntu ~}$ ulimit -Hn

1048576

root@Ubuntu ~}$ ulimit -Sn

1024

effect immediately without logout and reboot.

sysctl -p

security/limit.conf user level

$ ulimit -Hn
$ ulimit -Sn

~]$ ulimit -n -H

4096

~]$ ulimit -n -S

1024

ulimit -n <value>

root@instance-1:~#ulimit -Sn
100000
root@instance-1:~# ulimit -Hn
100000

 change ulimit settings

~]# su – oracle

~]$ ulimit -H -u

8096

~]$ ulimit -u -S

ulimit -u -H

root@instance-1:~# ulimit -H -u
31814
root@instance-1:~# ulimit -S -u
31814

ulimit -u 100000

root@instance-1:~# ulimit -u
31814
root@instance-1:~# ulimit -u 40000
root@instance-1:~# ulimit -u
40000

root@instance-1:~# ulimit -H -u
40000
root@instance-1:~# ulimit -S -u
40000

Restart needed to effect changes & also for applications too.

Aim:

1 connection & 1 process= 1-2 open files double the number.

‘listen.backlog‘, which defaults to -1 (unlimited). However, this value is also limited by the system (sysctl) value ‘net.core.somaxconn’, which defaults to 128 on many Linux systems.

root@instance-1:~# sysctl -a |grep net.core.somaxconn

net.core.somaxconn = 65536

This denotes the maximum number of file-handles a process can allocate. Default value is 1024*1024 (1048576) which should be enough for most machines. Actual limit depends on RLIMIT_NOFILE resource limit.

inode-max denotes the maximum number of inode handlers. This value should be 3-4 times larger than the value in file-max, since stdin, stdout and network sockets also need an inode struct to handle them. When you regularly run out of inodes, you need to increase this value.

max user processes linux limits.conf

umilit -u

root@instance-1:~# su – www-data -c “ulimit -Sa”
This account is currently not available.

Hard limits &. Soft limits

soft limit can be increased upto hard limit .

Finding ‘ulimit -a’ for process user nginx mysql php

cat /proc/PID/limits

root        8868  0.0  0.0 127044 24048 ?        Ss  May23  0:00 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;

cat /proc/8868/limits

max open files 1024

net.core.somaxconnection 128 to 65536 or

65535

Also see sysctl.conf

If you change the ulimit settings, you must restart your system for the changes to take effect.

root@instance-1:~# ulimit -aH
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 31814
max locked memory (kbytes, -l) 65536
max memory size (kbytes, -m) unlimited
open files (-n) 100000
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) unlimited
cpu time (seconds, -t) unlimited
max user processes (-u) 31814
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

to know ulimit soft limits

root@instance-1:~# ulimit -aS
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 31814
max locked memory (kbytes, -l) 65536
max memory size (kbytes, -m) unlimited
open files (-n) 100000
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) 31814
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

Recommended ulimit Settings for high performance

Every deployment may have unique requirements and settings; however, the following thresholds and settings are particularly important for mongod and mongos deployments:

• -f (file size): unlimited
• -t (cpu time): unlimited
• -v (virtual memory): unlimited
• -l (locked-in-memory size): unlimited
• -n (open files): 64000
• -m (memory size): unlimited
• -u (processes/threads): 64000