Max Open File Limit

Linux and Unix-Like Ubuntu
1

Ubuntu users,

I am configuring an Ubuntu 14.04 server as a load injector.

I have appended the hard and soft limits to /etc/security/limits.conf for any user (apart from root):

  •     hard   nofile      65536

  •     soft    nofile      65536

I am seeing the figure 65536 in numerous resources, but I am not sure why?

I am guessing that the system wide-limit should be larger than the user limit, so I have set this to �fs.file-max = 75000' in /etc/sysctl.conf. Is this correct?

Do I also need to set pam_limits on Debian based distros and where does this fit in?

And what limits does �ulimit -n' actually retrieve?

Many Thanks

Aidy

2

The only rule is: soft limit cannot be higher than hard limit
ulimit -n == ulimit -Sn == soft limit
ulimit -Hn == hard limit
ulimit -Ha == all hard limits
These are per-process limits.
I would leave fs.file-max to the default. It is usually much higher than the per-process limits. (The actual number is calculated by the available RAM.)

3

Hi MadeInGermany,

Thanks for your reply.

The kernel seems to set the soft and hard limits at 1024 and 4096 respectively.
$ ulimit -Sn
1024
$ ulimit -Hn
4096

But with a machine of 15GB RAM the system wide max limit is:
$ cat /proc/sys/fs/file-max
1529806

With this figure what would you suggest could be a sensible upper hard limit for a process?

Many Thanks

Aidy

4

The 4096 (default) makes sense in most cases.
A few server applications need more. But a few other applications crash or misbehave if they see very high limits.
Say Oracle would need 32768; then I would set it only for the particular functional user.

* hard nofile 4096
* soft nofile 1024
oracle hard nofile 32768
oracle soft nofile 32768
5

No need to change system wide, only per user.
Since, of course, you are not running your applications as root are you ?

As for the value required, this is application dependent.
What does that 'load injector' do?
What does the programmer/vendor of that load injector say about kernel parameters required for his software ?

Remember,max open files doesn't apply only to files but rather to file descriptors.
This covers a lot of possible functionality one application can do (sockets, pipes, files).

MadeInGermany - can you tell me where have you noticed failures with large values, if you can share, of course.

6

I have seen some java/eclipse programs wildly spawning new threads, until they reached the nofile limit or the nproc limit (if set). With the default nofile limits 1024/4096 the programs were running okay with about 300 threads.
Being an administrator I do not bother about what the eclipse programs are for.