nofile limit cannot be increased, only decreased

[Marc Schiffbauer]

Setting the maximum number of open files via pam's /etc/security/limits.conf (setting nofile) does only work for values less than 1024, not above

This seems to work on Gentoo, Red Hat and SuSE quite well so I started to look why it does not in ubuntu.

I found out that a patch applied durcing build is causing this:

in
  debian/patches-applied/027_pam_limits_better_init_allow_explicit_root

you find the following on line 59:

+ pl->limits[i].limit.rlim_max = 1024;

which seems to set the maximum for RLIMIT_NOFILE to 1024 which IMO is non-sense.

We have many servers that have it set to 65536 for big applications.
If I increase this rlim_max value, the default is still 1024 but I can rise it to limit.rlim_max -1

Please fix this by setting a reasonable value here. The kernel maximum is 2^20 = 1024*1024 = 1048576
(See "sysctl fs.nr_open" or "cat /proc/sys/fs/nr_open")

So I suggest setting it to 1024*1024 instead of 1024 value to not have a synthetic limit here

See attached patch for the patch which fixes it.

-Marc

[Marc Schiffbauer (mschiff)]

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=404836 is related

[Steve Langasek (vorlon)]

Thank you for taking the time to report this issue and help to improve Ubuntu.

After careful examination, I don't find any bug here. Setting limits via limits.conf works fine for me - and in fact, researching this shows that patch 027 was broken and was having no effect at all.

I think one of two things is happening here:

- you're setting a hard limit in limits.conf (ulimit -H -n) but are checking the soft limit (ulimit -n)
- you're trying to set a soft limit in limits.conf (user soft nofile...) without first raising the hard limit (user hard nofile...), so your soft limit change has no effect.

Lowering a hard limit will automatically lower the soft limit, but raising either limit will not automatically raise the other. I have no idea why any limit handling would work on other distros that doesn't work on Ubuntu unless there are differences in the in-kernel defaults.

[Sebastien Estienne (sebest)]

Maybe the confusion comes from the fact that '*' wildcard doesn't affect values for the root user.