Manpage of NICE
NICESection: Linux Programmer's Manual (2)
NAMEnice - change process priority
int nice(int inc);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
DESCRIPTIONnice() adds incto the nice value for the calling thread. (A higher nice value means a low 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 RLIMIT_NICEsoft limit; see getrlimit(2) for details.
RETURN VALUEOn success, the new nice value is returned (but see NOTES below). On error, -1 is returned, and errnois set appropriately.
- The calling process attempted to increase its priority by supplying a negative incbut has insufficient privileges. Under Linux, the CAP_SYS_NICEcapability is required. (But see the discussion of the RLIMIT_NICEresource limit in setrlimit(2).)
CONFORMING TOPOSIX.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.
NOTESFor further details on the nice value, see sched(7).
Note: 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 sched(7).
C library/kernel differencesPOSIX.1 specifies that nice() should return the new nice value. However, the raw Linux system call returns 0 on success. Likewise, the nice() wrapper function provided in glibc 2.2.3 and earlier returns 0 on success.
Since glibc 2.2.4, the nice() wrapper function provided by glibc provides conformance to POSIX.1 by calling getpriority(2) to obtain the new nice value, which is then returned to the caller.
SEE ALSOnice(1), renice(1), fork(2), getpriority(2), getrlimit(2), setpriority(2), capabilities(7), sched(7)
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