I have a question regarding ulimits. I have a CentOS 6 system and if I issue ‘ulimit –Hn’ I see that the maximum number of open file descriptors is set to 4096.

I tried to see if I could hit this limit so I wrote a small C program that loops through a bunch of files and fopen()’s 5000 of them, the code then waits for user input which it never gets therefore leaving the files open. I managed to run this code and the result of ‘lsof –u myuser | wc –l’ gave me a figure of around 5035.

Shouldn’t I have been prevented from opening this many files by ulimit?

Also, on a CentOS 6/7 system, where does a message get logged to if a process exceeds a ulimit – is it /var/log/secure?

Thanks

Starting with RHEL6 (and therefore derived distros such as CentOS6) in addition to /etc/security/limits.conf they began using files in /etc/security/limits.d. The latter is a directory and anything setup in that directory overrides what is in limits.conf file.

Specifically they added 90-nproc.conf to limits.d subdirectory so the values it contains are the active ones even though they didn't note this in limits.conf itself as they should have. It caused much gnashing of teeth and still bites people that haven't run across it yet.

Thanks MensaWater, do you have any idea why the limits don't seem to enforce or about the logging location?

Any method of testing ulimit would be useful, I'm trying to reproduce a reported problem.

Type "man ulimit" then go to the ulimit section of the bash man page it displays.

There it tells you:
-n The maximum number of open file descriptors (most systems
do not allow this value to be set)

Presumably your system doesn't really allow the value to be set.