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 process. (A higher nice value means a low priority.) Only the superuser may specify a negative increment, or priority increase. The range for nice values is described in getpriority(2).
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 Linux and (g)libc (earlier than glibc 2.2.4) return value is nonstandard, see below. SVr4 documents an additional EINVALerror code.
NOTESSUSv2 and POSIX.1 specify that nice() should return the new nice value. However, the Linux system call and the 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 getpriority(2).
Since glibc 2.2.4, nice() is implemented as a library function that calls 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 errnoto 0 before the call, and check its value when nice() returns -1.
SEE ALSOnice(1), renice(1), fork(2), getpriority(2), setpriority(2), capabilities(7), sched(7)
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