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nice(2) [centos man page]

NICE(2) 						     Linux Programmer's Manual							   NICE(2)

nice - change process priority SYNOPSIS
#include <unistd.h> int nice(int inc); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): nice(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE DESCRIPTION
nice() adds inc to 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 VALUE
On success, the new nice value is returned (but see NOTES below). On error, -1 is returned, and errno is set appropriately. ERRORS
EPERM The calling process attempted to increase its priority by supplying a negative inc but has insufficient privileges. Under Linux the CAP_SYS_NICE capability is required. (But see the discussion of the RLIMIT_NICE resource limit in setrlimit(2).) CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001. However, the Linux and (g)libc (earlier than glibc 2.2.4) return value is nonstandard, see below. SVr4 docu- ments an additional EINVAL error code. NOTES
SUSv2 and POSIX.1-2001 specify that nice() should return the new nice value. However, the Linux syscall 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 getprior- ity(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 errno to 0 before the call, and check its value when nice() returns -1. SEE ALSO
nice(1), renice(1), fork(2), getpriority(2), setpriority(2), capabilities(7) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at Linux 2007-07-26 NICE(2)

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nice(2) 							   System Calls 							   nice(2)

nice - change priority of a process SYNOPSIS
#include <unistd.h> int nice(int incr); DESCRIPTION
The nice() function allows a process to change its priority. The invoking process must be in a scheduling class that supports the nice(). The nice() function adds the value of incr to the nice value of the calling process. A process's nice value is a non-negative number for which a greater positive value results in lower CPU priority. A maximum nice value of (2 * NZERO) -1 and a minimum nice value of 0 are imposed by the system. NZERO is defined in <limits.h> with a default value of 20. Requests for values above or below these limits result in the nice value being set to the corresponding limit. A nice value of 40 is treated as 39. Calling the nice() function has no effect on the priority of processes or threads with policy SCHED_FIFO or SCHED_RR. Only a process with the {PRIV_PROC_PRIOCNTL} privilege can lower the nice value. RETURN VALUES
Upon successful completion, nice() returns the new nice value minus NZERO. Otherwise, -1 is returned, the process's nice value is not changed, and errno is set to indicate the error. ERRORS
The nice() function will fail if: EINVAL The nice() function is called by a process in a scheduling class other than time-sharing or fixed-priority. EPERM The incr argument is negative or greater than 40 and the {PRIV_PROC_PRIOCNTL} privilege is not asserted in the effective set of the calling process. USAGE
The priocntl(2) function is a more general interface to scheduler functions. Since -1 is a permissible return value in a successful situation, an application wishing to check for error situations should set errno to 0, then call nice(), and if it returns -1, check to see if errno is non-zero. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ SEE ALSO
nice(1), exec(2), priocntl(2), getpriority(3C), attributes(5), privileges(5), standards(5) SunOS 5.10 1 Apr 2004 nice(2)
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