Section: Linux Programmer's Manual (2)
nice - change process priority
int nice(int inc);
Feature Test Macro Requirements for glibc (see
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
to the nice value for the calling thread.
(A higher nice value means a lower priority.)
The range of the nice value is +19 (low priority) to -20 (high priority).
Attempts to set a nice value outside the range are clamped to the range.
Traditionally, only a privileged process could lower the nice value
(i.e., set a higher priority).
However, since Linux 2.6.12, an unprivileged process can decrease
the nice value of a target process that has a suitable
soft limit; see
On success, the new nice value is returned (but see NOTES below).
On error, -1 is returned, and
is set appropriately.
A successful call can legitimately return -1.
To detect an error, set
to 0 before the call, and check whether it is nonzero after
The calling process attempted to increase its priority by
supplying a negative
but has insufficient privileges.
Under Linux, the
capability is required.
(But see the discussion of the
resource limit in
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
However, the raw system call and (g)libc
(earlier than glibc 2.2.4) return value is nonstandard, see below.
For further details on the nice value, see
the addition of the "autogroup" feature in Linux 2.6.38 means that
the nice value no longer has its traditional effect in many circumstances.
For details, see
C library/kernel differences
POSIX.1 specifies that
should return the new nice value.
However, the raw Linux system call returns 0 on success.
wrapper function provided in glibc 2.2.3 and earlier returns 0 on success.
Since glibc 2.2.4, the
wrapper function provided by glibc provides conformance to POSIX.1 by calling
to obtain the new nice value, which is then returned to the caller.
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