renice value [ -t ] [ -g | -p | -u ] ID ...
ID can be a process group ID (pgid), process ID (pid), or a user name or user ID (user) depending on the option selected (-g, -p, or -u). By default, processes are specified by their process IDs.
Only root may set a lower nice value (higher scheduling priority) than the system default value of 20 (see the description of the -n option). To set a higher nice value (lower scheduling priority) than normal on a process, you must have appropriate privileges according to the set-user-ID (not the effective user ID) of the process.
If a user (including root) increases a process' nice value (lowers its priority) without specifying the -t option, this sets a new lower limit for the process' nice value. A user (excluding root) cannot reduce a process' nice value (raise the priority) unless they previously specified the -t option when increasing the process' nice value.
A user (excluding root) cannot reduce a process' nice value below the lower limit currently defined for it. There is no restriction on root's ability to raise and lower the priority of processes.
In the older form of the command, you can specify an absolute nice value (see nice(C)) rather than an increment to the existing nice value.
renice takes the following options:
If root specifies this option when increasing the nice value of a user's process, the user will be able to reduce the nice value subsequently.
Adjust the nice value so that the processes with IDs 987 and 32 have
a lower scheduling priority which can subsequently be increased:
renice -t -n 5 -p 987 32
Adjust the nice value so that processes currently in the process
groups with IDs 324 and 76 have a higher scheduling priority:
renice -n -5 -g 324 76
Adjust the nice value so that processes currently owned by the user
with ID 8 and by the user named cosgrove have a
lower scheduling priority:
renice -n 4 -u 8 cosgrove
If a user attempts to lower a process' nice value below the value currently permitted (either the default value or a new limit set by previous use of the -t option), renice sets the nice value to the lowest value allowed and fails silently.
ISO/IEC DIS 99452:1992, Information technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (IEEE Std 1003.21992);
X/Open CAE Specification, Commands and Utilities, Issue 4, 1992.