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[thirdparty/man-pages.git] / man2 / nice.2

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.\" Copyright (c) 1992 Drew Eckhardt <drew@cs.colorado.edu>, March 28, 1992
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.TH NICE 2 2005-09-20 "Linux 2.6.12" "Linux Programmer's Manual"
.SH NAME
nice \- change process priority
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "int nice(int " inc );
.SH DESCRIPTION
.BR nice ()
adds 
.I inc
to the nice value for the calling process.
(A large nice value means a low priority.)
Only the super\%user may specify a negative increment, or priority increase.
The range for nice values is described in
.BR getpriority (2).
.SH "RETURN VALUE"
On success, the new nice value is returned (but see NOTES below).
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EPERM
The calling process attempted to increase its priority by
supplying a negative
.IR inc
but has insufficient privileges.
Under Linux the
.B CAP_SYS_NICE
capability is required.
(But see the discussion of the 
.B RLIMIT_NICE
resource limit in
.BR setrlimit (2).)
.SH "CONFORMING TO"
SVr4, SVID EXT, AT&T, X/OPEN, 4.3BSD. However, the Linux and (g)libc
(earlier than glibc 2.2.4) return value is nonstandard, see below.
SVr4 documents an additional EINVAL error code.
.SH NOTES
SUSv2 and POSIX 1003.1-2003 specify that
.BR nice ()
should return the new nice value.
However, the Linux syscall and the
.BR nice ()
library function provided in older versions of (g)libc
(earlier than glibc 2.2.4) return 0 on success.
The new nice value can be found using
.BR getpriority (2).

Since glibc 2.2.4,
.BR nice ()
is implemented as a library function that calls
.BR getpriority (2)
to obtain the new nice value to be returned to the caller.
With this implementation,
a successful call can legitimately return \-1.
To reliably detect an error, set
.I errno
to 0 before the call, and check its value when
.BR nice ()
returns \-1.
.SH "SEE ALSO"
.BR nice (1),
.BR fork (2),
.BR getpriority (2),
.BR setpriority (2),
.BR capabilities (7),
.BR renice (8)