How to lsof report a higher number of open files than what ulimit says should be allowed

These limits came from a time where multiple "normal" users (not apps) would share the server, and we needed ways to protect them from using too many resources.

They are very low for high performance servers and we generally set them to a very high number. (24k or so) If you need higher numbers, you also need to change the sysctl file-max option (generally limited to 40k on ubuntu and 70k on rhel) .

Setting ulimit:

# ulimit -n 99999

Sysctl max files:

#sysctl -w fs.file-max=100000

Also, and very important, you may need to check if your application has a memory/file descriptor leak. Use lsof to see all it has open to see if they are valid or not. Don't try to change your system to work around applications bugs.

file-max is the maximum File Descriptors (FD) enforced on a kernel level, which cannot be surpassed by all processes without increasing. The ulimit is enforced on a process level, which can be less than the file-max.

There is no performance impact risk by increasing file-max. Modern distributions have the maximum FD set pretty high, whereas in the past it required kernel recompilation and modification to increase past 1024. I wouldn't increase system-wide unless you have a technical need.

The per-process configuration often needs tuned for serving a particular daemon be it either a database or a Web server. If you remove the limit entirely, that daemon could potentially exhaust all available system resources; meaning you would be unable to fix the problem except by pressing the reset button or power cycling. Of course, either of those is likely to result in corruption of any open files.