How to change the running process priority

The kernel determines which processes require more cpu time than others by the process' nice level, also called niceness. The higher the nice level of a process is, the less CPU time it will take from other processes. Nice levels range from -20 (the least “nice” level) to 19. Negative values can only set by root.

Adjusting the nice level is useful when running a non time-critical process that lasts long and uses large amounts of CPU time, such as compiling a kernel, on a system that also performs other tasks. Making such a process “nicer”, ensures that the other tasks, for example a webserver, will have a higher priority.

Calling nice without any parameters prints the current niceness:

nikesh@poison:~> nice
0

Running nice command increments the current nice level for the given command by 10. Using nice -n level command lets you specify a new niceness relative to the current one.

To change the niceness of a running process, use renice priority -p process id, for example:

renice +5 3266

To renice all processes owned by a specific user, use the option -u user. Process groups are reniced by the option -g process group id.