Change the execution priority for
command, or, if
none is given, change priority for the current shell.
(See also nice in Section 2.)
The priority range is -20 to 20, with a default of 4.
The range seems backwards: -20 gives the highest priority
(fastest execution); 20 gives the lowest.
n to the priority value (lower job priority).
n from the priority value (raise job priority).
Privileged users only.