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       nice - change process priority


       #include <unistd.h>

       int nice(int inc);


       nice()  adds  inc  to the nice value for the calling process.  (A large
       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).


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


       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).)


       SVr4, SVID EXT, AT&T, X/OPEN, 4.3BSD. However, the  Linux  and  (g)libc
       (earlier  than  glibc  2.2.4)  return  value is nonstandard, see below.
       SVr4 documents an additional EINVAL error code.


       SUSv2 and POSIX 1003.1-2003 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.


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