soft and hard limits for nproc value in /etc/security/limits.conf file

kraljic · 07-13-2015, 04:53 AM

OS version : RHEL 6.5

Below is an excerpt from /etc/security/limits.conf file for OS User named appusr in our server

appusr soft nproc 2047
appusr hard nproc 16384

Question1.
What will happen if appusr has already spawned 2047 processes and wants to spawn 2048th process ?

I just want to know the impact of breaching the soft limit of 2047

Question2.
In Linux , is there any way I could quickly spawn/fork n number of dummy processes using a loop or something?

rtmistler · 07-13-2015, 05:50 AM

Question 1 has been answered in another thread HERE by way of saying that the soft limit merely means it is software adjustable, you cannot create processes beyond that limit value.

For question 2, yes you can, write some C code in a limiting loop to use and re-use fork() to create processes. Check the return code from fork(), keep track of how many processes you have created, and check errno for cases when things fail.

kraljic · 07-13-2015, 07:43 AM

Hi Rtmistler,

Thank you for answering Question2.

Regarding Question1.
Didn't quite understand what you meant by "soft limit merely means it is software adjustable, you cannot create processes beyond that limit value" .
Isn't that a mutually contradicting statement ?

rtmistler · 07-13-2015, 08:13 AM

Quote:

Originally Posted by kraljic

Hi Rtmistler,

Thank you for answering Question2.

Regarding Question1.
Didn't quite understand what you meant by "soft limit merely means it is software adjustable, you cannot create processes beyond that limit value" .
Isn't that a mutually contradicting statement ?

If you review the former question, the OP incorrectly had the impression that soft limit was some sort of warning point. They tested and found that soft limit was a true limit, and so their conjecture was that "soft" was not soft at all, but instead the same as hard. The correction was to explain to them that the limit is a true governor, however that the limit can be adjusted by changing system settings. See limits.conf(5) and observe ulimit(1) with the -u option.