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

       nice - change process priority

       #include <unistd.h>

       int nice(int inc);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       nice() adds inc 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 RLIMIT_NICE soft limit; see getrlimit(2) for details.

       On success, the new nice value is returned (but see NOTES below).  On
       error, -1 is returned, and errno is set to indicate the error.

       A successful call can legitimately return -1.  To detect an error, set
       errno to 0 before the call, and check whether it is nonzero after nice()
       returns -1.

       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).)

       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

       For 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 differences
       POSIX.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

       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.

       nice(1), renice(1), fork(2), getpriority(2), getrlimit(2),
       setpriority(2), capabilities(7), sched(7)

       This page is part of release 5.11 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                              2021-03-22                            NICE(2)