2:nice

From Linux Man Pages

      nice - change process priority
      

Contents 1 SYNOPSIS 2 DESCRIPTION 3 RETURN VALUE 4 ERRORS 5 CONFORMING TO 6 NOTES 7 RELATED 8 CATEGORY

SYNOPSIS

      #include <unistd.h>
 
      int nice(int inc);

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 get-
      priority(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  nonstan-
      dard, see below.  SVr4 documents 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 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 errno to 0 before the call, and check its value when nice() returns -1.

RELATED

      nice(1), fork(2), getpriority(2), setpriority(2), capabilities(7), renice(8)

CATEGORY