14

I have added a line in /etc/security/limits.conf to increase the number of open files.

*    hard nofile 4096
root hard nofile 16384

However when I run ulimit -n it says 1024 which is the default value. I did a logout and login but still see 1024. How can I apply the change?

7

If you're using bash, ulimit -n will only display the soft limit. To get the hard limit, you need to do ulimit -Hn.

On my system, I see this:

$ ulimit -n
1024
$ ulimit -Hn
4096
16

Changes made by ulimit command:

$ ulimit -n 4096
$ ulimit -Hn 16384

will apply only for current user and session. In order to make it permanent, you have to modify /etc/security/limits.conf by adding your limits:

* soft nofile 4096
* hard nofile 16384

However, wildcard * won't apply for root user. In order to do so, you have to state it explicitly:

* soft nofile 4096
* hard nofile 16384
root soft nofile 4096
root hard nofile 16384

These limits will be applied after reboot.

If you want to apply changes without reboot, modify /etc/pam.d/common-session by adding this line at the end of file:

session required pam_limits.so

Upon next login you should see updated limits, you can check them (soft and hard limits):

$ ulimit -a
$ ulimit -Ha
  • 2
    I had an issue with this approach which was really strange. I am using Ubuntu 14 and enabled pam_limits.so in /etc/pam.d/common-session. I have configured in /etc/security/limits.conf user x to have hard and soft limits for nofile 64000. sudo -u x then ulimit -a shows me that the changes were not applied. I realized that su and sudo have different pam configurations so in order to make it work properly I needed to enable the pam_limits.so in /etc/pam.d/common-session-noninteractive. If you are wondering what is the use case - I use ansible and sudo to change user. – hahcho Dec 1 '17 at 10:10
  • 1
    For some reason, I had to add it to /etc/pam.d/common-session-noninteractive for it to work. – Sumit Nov 29 '18 at 5:37

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