`nice`

Run a program at an altered priority (POSIX)

Syntax:

nice [-nprioritylevels] command [arguments]...

Deprecated:

nice [-prioritylevels] command [arguments]...

Options:

-prioritylevels: Deprecated. This is the historical method of specifying the amount to adjust the current priority by. Specifying -1 lowers the priority by one, while specifying --1 boosts the priority by one.
-n prioritylevels: Specify the amount to adjust the current priority by when running the command. The command is run at a priority level of the current priority minus prioritylevels.
command [arguments]...: The command to run at the altered priority.

Description:

The nice utility invokes the specified command with a modified priority, usually making the command behave "more nicely" towards competing processes.

If no prioritylevels option is specified, the program is invoked at a priority that's one level lower than the parent's current priority (i.e. it is invoked with a "nice increment" of 1).

If a prioritylevels option is specified, it's subtracted from the parent's current priority and the program is invoked at the resultant priority. If the resulting priority isn't a valid priority, nice writes a diagnostic message to the standard error and exits with a status of 1.

If you enter:	`nice`:
A positive value (e.g. `-n2` or `-n+2`)	Lowers the priority of the program, making it "nice"
A negative value (e.g. `-n-2`)	Raises the priority of the program, making it "mean"

You can adjust the priority as follows:

If you're:	You can change to any priority:
A non-`root` user	From 1 to 63
`root`	From 1 to 255

You can change the range of privileged priorities with the -P option for procnto.

Examples:

Run make at one priority lower than the parent's priority (be nice):

nice make application

Run make at two priorities lower than the parent's priority (be nicer):

nice -n2 make application

Run make at two priorities higher than the parent's priority (be mean):

nice -n-2 make application

Exit status:

If the operation is successful, the exit status of the invoked command is returned. If an error occurs, the exit status is as follows:

1: Invalid command-line parameters were given or the user requested an invalid priority.
126: The command specified didn't exist.
127: The command couldn't be started for some other reason.

Caveats:

In contrast to other operating systems, the QNX Neutrino interpretation of the nice value substantially affects the priority of the process. Rather than representing a fraction of a priority, the granularity of the nice value in QNX Neutrino is of a "whole" priority level. For example, where the following has a marginal effect on the execution of myprog on some operating systems:

nice -n5 myprog

on QNX Neutrino it lowers the priority of myprog by five full priority levels, and could have a significant effect on myprog's execution time.