Ubuntu – Apply ulimit globally on Ubuntu

These limits came from a time where multiple "normal" users (not apps) would share the server, and we needed ways to protect them from using too many resources.

They are very low for high performance servers and we generally set them to a very high number. (24k or so) If you need higher numbers, you also need to change the sysctl file-max option (generally limited to 40k on ubuntu and 70k on rhel) .

Setting ulimit:

# ulimit -n 99999

Sysctl max files:

#sysctl -w fs.file-max=100000

Also, and very important, you may need to check if your application has a memory/file descriptor leak. Use lsof to see all it has open to see if they are valid or not. Don't try to change your system to work around applications bugs.

[edit: explained details for clarity]

I suspect you checked the ulimit for the different user than mysql ;)

You don't have to reboot after changing limits.conf. You have to turn on use of this file in the corresponding PAM service in /etc/pam.d/.

Do grep pam_limits /etc/pam.d/* to have a clue in which situation limits.conf will be used.

For example, change in limits.conf for can be visible in the shell invoked as sudo -u user bash but doesn't when run as sudo su - user - that's because on Ubuntu default setting goes like this:

$ grep limits /etc/pam.d/*|grep su
/etc/pam.d/su:# session required pam_limits.so
/etc/pam.d/sudo:session required pam_limits.so

So if you checked limits using sudo su - mysql then there was a mess -- su didn't turn the limits on. You can check which pam service is being run by watching /var/log/auth.log.

For all possible types of invocation of your mysql it should be safe to modify pam.d/other or just pam.d/common-session.