| .\" Copyright (c) 1992 Drew Eckhardt <drew@cs.colorado.edu>, March 28, 1992 |
| .\" |
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| .\" Modified by Michael Haardt <michael@moria.de> |
| .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu> |
| .\" Modified 1996-11-04 by Eric S. Raymond <esr@thyrsus.com> |
| .\" Modified 2001-06-04 by aeb |
| .\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com> |
| .\" |
| .TH NICE 2 2017-09-15 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| nice \- change process priority |
| .SH SYNOPSIS |
| .B #include <unistd.h> |
| .PP |
| .BI "int nice(int " inc ); |
| .PP |
| .in -4n |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .in |
| .PP |
| .BR nice (): |
| _XOPEN_SOURCE |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .SH DESCRIPTION |
| .BR nice () |
| adds |
| .I inc |
| to the nice value for the calling thread. |
| (A higher nice value means a low priority.) |
| .PP |
| 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. |
| .PP |
| 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 |
| .BR RLIMIT_NICE |
| soft limit; see |
| .BR getrlimit (2) |
| for details. |
| .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. |
| .PP |
| A successful call can legitimately return \-1. |
| To detect an error, set |
| .I errno |
| to 0 before the call, and check whether it is nonzero after |
| .BR nice () |
| returns \-1. |
| .SH ERRORS |
| .TP |
| .B EPERM |
| The calling process attempted to increase its priority by |
| supplying a negative |
| .I 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 |
| 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. |
| .\" SVr4 documents an additional |
| .\" .B EINVAL |
| .\" error code. |
| .SH NOTES |
| For further details on the nice value, see |
| .BR sched (7). |
| .PP |
| .IR 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 |
| .BR sched (7). |
| .\" |
| .SS C library/kernel differences |
| POSIX.1 specifies that |
| .BR nice () |
| should return the new nice value. |
| However, the raw Linux system call returns 0 on success. |
| Likewise, the |
| .BR nice () |
| wrapper function provided in glibc 2.2.3 and earlier returns 0 on success. |
| .PP |
| Since glibc 2.2.4, the |
| .BR nice () |
| wrapper function provided by glibc provides conformance to POSIX.1 by calling |
| .BR getpriority (2) |
| to obtain the new nice value, which is then returned to the caller. |
| .SH SEE ALSO |
| .BR nice (1), |
| .BR renice (1), |
| .BR fork (2), |
| .BR getpriority (2), |
| .BR getrlimit (2), |
| .BR setpriority (2), |
| .BR capabilities (7), |
| .BR sched (7) |