NICE(1) USER COMMANDS NICE(1)
NAME
nice - run a command at low priority
SYNOPSIS
nice [ -number ] command [ arguments ]
DESCRIPTION
There are two distinct versions of nice: it is built in to
the C shell, and is an executable program available in
/usr/bin/nice for use with the Bourne shell.
nice executes command with the nice value number. The nice
value is one of the factors used by the kernel to determine
a process's scheduling priority. Scheduling priorities
range from 0 to 127. The higher the value, the lower the
command's scheduling priority, and the lower the value, the
higher the command's scheduling priority. In addition to
the nice value, the kernel also recent CPU usage by the pro-
cess, the time the process has been waiting to run, and
other factors to arrive at scheduling priority.
If the number argument is present, the nice value is incre-
mented or decremented by that amount, between the limits -20
and 19. If there is no number argument, the default nice
value is 10 for the Bourne shell, and 4 for the C-shell.
The super-user may run commands with priority higher than
normal by using negative nice values, such as -10.
EXAMPLES
The following examples illustrate the use of nice values for
users (not the super-user) using /usr/bin/nice. The exam-
ples use the -l option to ps(1) because it shows both the
nice value and the kernel scheduling priority. Notice the
NI and PRI columns. In the first example, the user doesn't
use nice, so the niceness is zero, the default value, which
is reflected by 0 in the NI column. The corresponding pro-
cess scheduling priority is shown in the PRI column as 28
(this may vary because of the other factors the kernel's
scheduler uses).
In the second example, the user uses a nice value of 10, and
the corresponding priority is 53, a higher numerical value
but a lower priority. Notice that this is the same as:
example% nice ps -l
because the default nice value is 10.
In the third example, the user asks that the nice value be
incremented by 20, but it's shown as 19 under NI, because
that's the upper limit of niceness.
A fourth example shows the error message when an ordinary
user tries to decrement the nice value.
example% ps -l
F UID PID PPID CP PRI NI SZ RSS WCHAN STAT TT TIME COMMAND
...
19442 16623 9725 12 28 0 120 336 R p2 0:00 ps -l
...
example% nice -10 ps -l
F UID PID PPID CP PRI NI SZ RSS WCHAN STAT TT TIME COMMAND
...
19442 16608 16606 32 53 10 120 328 R N p2 0:00 ps -l
...
example% nice -20 ps -l
F UID PID PPID CP PRI NI SZ RSS WCHAN STAT TT TIME COMMAND
...
19442 16609 16606 37 72 19 120 328 R N p2 0:00 ps -l
...
example% nice --20 ps -l
nice: setpriority: Permission denied
example%
SEE ALSO
csh(1), getpriority(2), nice(3V), pstat(8), renice(8)
DIAGNOSTICS
nice returns the exit status of the subject command.
BUGS
The nice command has a different syntax than the
/usr/bin/nice command described here. It uses the plus
sign, +, to increment nice values, for example:
example% nice +number
increments the nice value by number. It uses a single a
minus sign, -, to decrement nice values for super-user.
Sun Release 4.1 Last change: 9 September 1987
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