renice

Renice is a command used on Unix-like systems to modify the scheduling priority of running processes by changing their niceness value. The niceness value is an integer from -20 (highest priority) to 19 (lowest priority). The default value for new processes is 0. Lower niceness numbers mean higher priority; higher numbers mean lower priority. Renice affects the kernel’s scheduler for the target processes; it does not directly control CPU time but influences scheduling decisions.

Usage and targets: Renice takes a new niceness value and a target. Targets can be specified by process ID (-p pid), process group (-g pgid), or user (-u username). The -n option specifies the new niceness value. Examples: renice -n 10 -p 1234 sets the niceness of process 1234 to 10. renice -n -5 -p 1234 attempts to set a higher priority and requires elevated privileges (root). renice -n 5 -u alice adjusts all processes owned by alice to 5. renice -n 3 -g 2000 adjusts all processes in group 2000 to 3.

Privileges: Regular users may only increase niceness values for their own processes (i.e., move toward 19). Decreasing niceness (lower values) generally requires root or appropriate privileges on the system. Some systems implement additional policy controls that restrict changes further.

Variants and related commands: Renice is part of the procps (procps-ng) package on Linux and has equivalents in other Unix-like systems. It is commonly used with the nice command to start processes with a given niceness value or to adjust priorities after launch.

See also: nice, ps, top, schedulers.