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On Unix systems with BSD-style priority schemes, once a job is running, you can use the renice(8) command to change the job's priority:
% /etc/renice priority-p pid % /etc/renice priority -g pgrp % /etc/renice priority -u uname
where priority is the new nice level (Section 26.5) for the job. It must be a signed integer between -20 and 20. pid is the ID number (Section 24.3) (as shown by ps (Section 24.5)) of the process you want to change. pgrp is the number of a process group (Section 24.3), as shown by ps -l; this version of the command modifies the priority of all commands in a process group. uname may be a user's name, as shown in /etc/passwd; this form of the command modifies the priority of all jobs submitted by the user.
A nice level of 19 is the "nicest": the process will run only when nothing else on the system wants to. Negative values make a process get a greater percentage of the CPU's time than the default niceness (which is 0). Again, only the superuser can lower the nice number (raise a process' priority). Users can only raise the nice number (lower the priority), and they can modify the priorities of only the jobs they started.
-- ML
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| 26.6. A nice Gotcha |  | VI. Scripting |
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