NAME
nice —
adjust scheduling priority
SYNOPSIS
nice |
nice |
[-n diff]
program
[argument]… |
DESCRIPTION
With program, adds diff (default 10) to the niceness, then executes program arguments; otherwise writes current niceness to the standard output stream.
Niceness, ranging [-20, 19], reflects the (inverse) scheduling priority. diff may be any integer, but will be clamped to that range by the system; lowering niceness (increasing priority) is a privileged operation: if it fails, a diagnostic is issued, but program is still executed.
OPTIONS
-n,--adjustment=diff- Alter niceness by this much. Default: 10.
ENVIRONMENT
PATH- In which program is searched, confer execvp(3).
EXIT STATUS
- 127
- program wasn't found.
- 126
- program exists, but couldn't be executed for a different reason.
- 125
- Internal error.
- All others
- returned by program.
SEE ALSO
STANDARDS
Conforms to IEEE Std 1003.1-2008 (“POSIX.1”).
The no-program behaviour is an extension, also present on the GNU system.
The default -n value is
10 on all known systems; the upper end of the range is
20, not 19, on
OpenBSD.
HISTORY
A way to alter scheduling priority first appeared in Version 2 AT&T UNIX as hog(II), "set low-priority status" in the index and:
Moving the caller to the low-priority queue, which "background jobs that execute for a long time should do". The job was moved back to the regular queue "as soon as the process is dismissed for any reason other than quantum overflow" (when a syscall is made).Version 3 AT&T UNIX renamed it to nice(II), noting "Once done, there is no way to restore a process to normal priority.".
Version 4 AT&T UNIX sees
nice(II) amended with a priority argument and a noted range
of "20 to -220" (incorrect, of course — it's a maximum of
19 and a minimum of
0 for regular users and
CHAR_MIN for root).
16 is
recommended for "users who wish to execute long-running programs
without flak from the administration.". Indeed, this is what the new
nice(I) command does.
Version 6 AT&T UNIX
nice(I) defaults to
4 and accepts a
-niceness argument to override
it.
Version 7 AT&T UNIX defaults to
10 (and uses PATH
to find program).
nice(2) now applies an increment, exactly like today, and
notes a [-20, 20] range (wrong, of
course; the actual range is [-20, 19],
like today).
X/Open Portability Guide Issue 4
(“XPG4”) standardises it, except it invents
-n diff to supersede
-diff, noting the latter as
obsolete, as it violates the Utility Syntax Guidelines;
IEEE Std 1003.1-2001 (“POSIX.1”)
removes it. -n was likely chosen because the
Version 6 AT&T UNIX and later usage
strings are
usage: nice [ -n ]
command