Working with ulimits and open file descriptors

Yet another in the long list of things I always forget how to do between needing to do them...

Cheatsheet to working with ulimits and too many open files.

list how many open file descriptors a process has

lsof -P [pid] | wc -l

ls /proc/[pid]/fd | wc -l (cheaper)

look at limits for a specific process

cat /proc/[pid]/limits

set limits for a user

futz with /etc/security/limits.conf or /etc/security/limits.d/*

show ulimits for the current process

ulimit -a

set number of open file handle limit for the current process (and processes spawned from this one)

ulimit -n 16384 (note - only root can raise hard limits)

Hope that helps, future self.