Resource Limits

RLIMIT_NICE (2.6.12)

Process nice value has range -20 (high) to +19 (low); influences kernel scheduler.
In kernels < 2.6.12, only privileged processes CAP_SYS_NICE could raise nice scheduling parameter.
Since kernel 2.6.12, RLIMIT_NICE can be used to allow unprivileged process to set a negative nice value.
Ceiling for nice value is calculated as 20 - rlim_cur, where rlim_cur is the current RLIMIT_NICE soft resource limit.
E.g., if RLIMIT_NICE is 25, then nice value can be raised to -5.
Linux specific.