What does “soft/hard nofile” mean on Linux

Question

When I tried to install a software on RedHat EL5, I got the error that the expected value of soft/hard nofile is 4096 while the default is 1024. I managed to increase the number

Answer 1

These are: a 'soft' and a 'hard' limit for number of files a process may have opened at a time. Both limit the same resource (no relation to hard links or anything). The difference is: the soft limit may be changed later, up to the hard limit value, by the process running with these limits and hard limit can only be lowered – the process cannot assign itself more resources by increasing the hard limit (except processes running with superuser privileges (as root)).

Similar limits can be set for other system resources: system memory, CPU time, etc. See the setrlimit(2) manual page or the description of your shell's ulimit build-in command (e.g. in the bash(1) manual page.