Cannot Increase open file limit past 4096 (Ubuntu)

I'm on Ubuntu 17.04. Trying to increase the open file limit, and none of the instructions I've found online are working. I can go up to 4096, but can't go past that.

$ ulimit -n
1024
$ ulimit -n 4096
$ ulimit -n
4096

That works. This doesn't:

$ ulimit -n 4097
bash: ulimit: open files: cannot modify limit: Operation not permitted

It appears to be because of the hard limit:

$ ulimit -Hn
4096

I've tried adding these lines to /etc/security/limits.conf:

* hard nofile 65535
* soft nofile 65535
root soft nofile 65535
root hard nofile 65535

Also added this line to /etc/pam.d/common-session and /etc/pam.d/common-session-noninteractive:

session required pam_limits.so

Since doing that, I've rebooted my computer. Changes to limits.conf don't seem to affect anything. The hard limit is still stuck at 4096, preventing me from going any higher. How do I increase my open files limit?

Here's some additional config info:

$ cat /proc/sys/fs/file-max
1624668

5 Answers

OK, I finally figured this out. The limits I was setting in /etc/security/limits.conf were indeed being applied, but not to the graphical login. This can be verified from a terminal window:

$ ulimit -n
4096
$ su mkasberg
Password:
$ ulimit -n
65535

More research led me to this bug report, which got me pointed in the right direction. In order to modify the limit that is used by the login shell, we need to add the following line to /etc/systemd/user.conf:

DefaultLimitNOFILE=65535

That change works, but only affecting the soft limit. (Leaving us capped with a hard limit of 4096 still.) In order to affect the hard limit, we must modify /etc/systemd/system.conf with the same changes.

The changes I made in /etc/pam.d were not necessarily; it's already working, at least on Ubuntu. Also, it was not necessary to add the lines root and * in limits.conf; adding the username alone (mkasberg in my case) was sufficient.

In Summary

If you want to increase the limit shown by ulimit -n, you should:

• Modify /etc/systemd/user.conf and /etc/systemd/system.conf with the following line (this takes care of graphical login):

   DefaultLimitNOFILE=65535

• Modify /etc/security/limits.conf with the following lines (this takes care of non-GUI login):

   mkasberg hard nofile 65535 mkasberg soft nofile 65535

• Reboot your computer for changes to take effect.

No need to change anything in the /etc/security/limits.conf file, it is ignored if you are using systemd.

(reproducing a modified answer to another question on the network...)

An alternative for those who prefer not to edit the default /etc/systemd/system.conf and /etc/systemd/user/conf files:

1. create a new file /etc/systemd/system.conf.d/limits.conf with these contents:

   [Manager]
   DefaultLimitNOFILE=65535

2. run systemctl daemon-reexec as root

3. logout and login again

4. check your new limit with ulimit -n.

Refer to the systemd-system.conf manpage for details.

TL;DR I felt the need to concentrate the answers, so they're easier to find. Took me ages to get all the pieces together to make it work correctly ...

There are 2 locations to be considered.

1. GUI session

   $ grep DefaultLimitNOFILE /etc/systemd/system.conf
   DefaultLimitNOFILE=65535

   or better here:

   $ grep NOFILE /etc/systemd/system.conf.d/limits.conf
   DefaultLimitNOFILE=65535

2. shell environment

   $ grep nofile /etc/security/limits.conf
   user soft nofile 65535
   user hard nofile 65535`

   or better here:

   $ grep nofile /etc/security/limits.d/user.conf
   user soft nofile 65535
   user hard nofile 65535

3. After altering the settings in the above files, reboot and then check the limits with:ulimit -n -Hn -Sn

1. edit /etc/systemd/system/sonar.service

2. add these two line under Service

[Service]

LimitMEMLOCK=infinity

LimitNOFILE=65535

3. systemctl daemon-reload
4. systemctl restart sonar

this works for me.

Using Ubuntu 17.04 I got the described hard limit:

:~$ ulimit -Hn
4096

I could lower it using ulimit, but not increase it, just as the question describes it. ulimit manual describes:

only root can increase the hard limit.

So I tried to set a higher limit in /etc/security/limits.conf like this:

user hard nofile 9999

and a fresh login like ssh localhost -l user gave me the new limit:

:~$ ulimit -Hn
9999

I hope this works for you too.