nice(1)nice(1)NAMEnice - run a command at nondefault priority
SYNOPSIS
command [command_args]
command [command_args]
DESCRIPTION
The command executes command at a nondefault CPU scheduling priority.
(The name is derived from being "nice" to other system users by running
large programs at lower priority.)
Arguments
The command-line arguments are as follows:
priority_change The difference between the system
nice value (relative priority) of
the current (or parent) process
and the actual system nice value
at which command is to run.
An unsigned value increases the
system nice value for command,
causing it to run at lower prior‐
ity.
A negative value requires supe‐
ruser privileges, and assigns a
lower system nice value (higher
priority) to command. If the cur‐
rent process is not privileged,
the value is silently treated as
if it were 0.
If the value of priority_change
would result in a system nice
value outside the range 0 through
39, the corresponding limit value
of 0 or 39 is used instead.
Note that a positive prior‐
ity_change (lower priority) has a
single option character before the
numeric value; a negative (higher
priority) priority_change has two:
the option character followed by
the minus sign If is not speci‐
fied, it defaults to
command A program, HP-UX command, user
shell script, etc. to be executed
at the nondefault priority. com‐
mand can be run as a foreground or
background process.
If command is run as a background
process, any nice priority_change
made by the shell executes all
background processes via is in
addition to that specified in the
command line.
command_args Any arguments recognized by com‐
mand.
Process Priorities
All processes have an associated system nice value which
is used to compute the instantaneous-priority of the
process when it is scheduled to run. Normally, all pro‐
cesses inherit the system nice value of their parent
process when they are spawned. The shell etc.) can cre‐
ate a child process with a different priority from the
current shell process by spawning the child process via
the command. If the priority_change value is unsigned
(positive), the child process is nicer (lower in prior‐
ity) relative to the parent. If the priority_change
value is negative, the child process runs at a higher
priority with a greater share of available system
resources. To spawn a higher priority child process, the
parent process must be owned by a user who has the appro‐
priate privileges.
At boot-up, the system starts the process at a system
nice value of 20 (system default). On most systems, all
processes (down to the login shells) inherit this prior‐
ity. Starting from their individual login shell pro‐
cesses, users can alter the system nice value of descen‐
dent processes to as much as 39, or, with appropriate
privileges, as little as 0. A system nice value of 0
establishes an extremely high priority, whereas a value
of 39 indicates a very low priority.
Ordinary users can only increase the system nice value of
any child process relative to the current process; i.e.,
priority_change must be a positive (unsigned) value,
resulting in a lower priority. To start a child process
at a lower system nice value (higher priority) than the
current process, the user must have the appropriate priv‐
ileges, regardless of the relative nice-priority value
desired.
For example, using the command
from a login shell whose current nice value is 20 spawns
a subshell with a system nice value of 30. Attempting to
use
from the new shell to spawn another subshell whose system
nice value would be 28, is rejected (unless the user has
appropriate privileges), even though the resulting system
nice value would be less than the priority of the origi‐
nal login shell process.
The system nice value for current processes is listed
under the column produced by the command (see ps(1)).
Background Processes
Foreground processes are run at same system nice value as
the parent shell. Background processes spawned by run at
the equivalent of a by default. If a background process
is started via from any priority_change specified in the
command is added to default Thus the command
runs at a system nice value of 36 if executed from
EXTERNAL INFLUENCES
Environment Variables
determines the language in which messages are displayed.
If is not specified in the environment or is set to the
empty string, the value of is used as a default for each
unspecified or empty variable. If is not specified or is
set to the empty string, a default of "C" (see lang(5))
is used instead of
If any internationalization variable contains an invalid
setting, behaves as if all internationalization variables
are set to "C". See environ(5).
International Code Set Support
Single- and multi-byte character code sets are supported.
RETURN VALUE
returns the value returned by command.
EXAMPLES
The following examples assume the current process is run‐
ning with a system nice value of 20 and is executed from
the Korn shell (see ksh(1)).
Run a program named in the current directory at the
default priority_change of 10 (system nice value of 30):
Run the same program in the background using a system
nice value of 36 (priority_change=12 plus 4 for the Korn
shell):
As a user with appropriate privileges, run as a fore‐
ground process with a system nice value of 6:
WARNINGS
The C shell, has a built-in command with different syn‐
tax. See csh(1) for details.
SEE ALSOcsh(1), ksh(1), nohup(1), sh-posix(1), sh(1), renice(1M),
nice(2).
STANDARDS CONFORMANCEnice(1)
