Check open file descriptor limit, warn if low

[cryptocode]

Sample output (stderr and log)

WARNING: The file descriptor limit on this system may be too low (512) 
and should be increased to at least 16384.

This can be tested with docker run --ulimit nofile=512:1024 ...

[SergiySW]

Could rlim_cur be lower than rlim_max ?

[cryptocode]

@SergiySW yes, but the soft limit (rlim_cur) is what processes run into, rlim_max is the system hard limit, for processes trying to increase the limit programmatically. Do you mean rlim_max should be checked still?

[SergiySW]

@SergiySW yes, but the soft limit (rlim_cur) is what processes run into, rlim_max is the system hard limit, for processes trying to increase the limit programmatically. Do you mean rlim_max should be checked still?

Yes, I wonder if need to check it as well