Change the maximum number of open files in ubuntu 18.10

The procedure changed on recent ubuntu compared to what I used to do. I used change /etc/security/limits.conf.

The procedure on ubuntu 18.10 that worked for me is this.

1. Go to /etc/systemd/system.conf

2. Uncomment DefaultLimitNOFILE and set your limit there, e.g.

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

3. Restart

4. Profit

Before:

$ ulimit -n
1024
$ ulimit -Sn
1024
$ ulimit -Hn
1048576

After:

$ ulimit -n
65535
$ ulimit -Sn
65535
$ ulimit -Hn
65535

The limits can be controlled by systemd and this is what we do here — instruct systemd to set it to 65k. Note that this setting will apply to all users, which is OK for a laptop or a workstation. On a server you may need a finer grained settings and you should look for a different method.