Ubuntu – nofile ulimit -n on Ubuntu 14.04 LTS

The ulimit command by default changes the HARD limits, which you (a user) can lower, but cannot raise.

Use the -S option to change the SOFT limit, which can range from 0-{HARD}.

I have actually aliased ulimit to ulimit -S, so it defaults to the soft limits all the time.

alias ulimit='ulimit -S'

As for your issue, you're missing a column in your entries in /etc/security/limits.conf.

There should be FOUR columns, but the first is missing in your example.

* soft nofile 4096
* hard nofile 4096

The first column describes WHO the limit is to apply for. '*' is a wildcard, meaning all users. To raise the limits for root, you have to explicitly enter 'root' instead of '*'.

You also need to edit /etc/pam.d/common-session* and add the following line to the end:

session required pam_limits.so

I increased the number of files limits for everyone this way (segment from /etc/security/limits.conf):

#        - memlock - max locked-in-memory address space (KB)
#        - nofile - max number of open files (Doug: - so Samba will not complain)
* - nofile 16384
#        - rss - max resident set size (KB)
#        - stack - max stack size (KB)

That was on a 12.04 server. However, I tested 100000 on my 14.04 server and it worked fine. (Edit: also checked on 20.04)

~/config/security$ ulimit -n
16384

EDIT: For most applications that is enough, but it doesn't change the default value for root:

# ulimit -n
1024

If the number also needs to be changed for root, then (2020.09.04 - I now use 131,072):

#        - memlock - max locked-in-memory address space (KB)
#        - nofile - max number of open file descriptors
* - nofile 131072
root - nofile 131072
#        - rss - max resident set size (KB)
#        - stack - max stack size (KB)

And so:

$ sudo su
# ulimit -n
131072