NAME

       getpriority, setpriority - get and set the nice value

SYNOPSIS

       #include <sys/resource.h>

       int getpriority(int which, id_t who);
       int setpriority(int which, id_t who, int value);

DESCRIPTION

       The  getpriority()  function  shall  obtain the nice value of a process, process group, or
       user. The setpriority() function shall set the nice value of a process, process group,  or
       user to value+ {NZERO}.

       Target  processes  are  specified  by the values of the which and who arguments. The which
       argument may be one of  the  following  values:  PRIO_PROCESS,  PRIO_PGRP,  or  PRIO_USER,
       indicating that the who argument is to be interpreted as a process ID, a process group ID,
       or an effective user ID, respectively.  A 0 value  for  the  who  argument  specifies  the
       current process, process group, or user.

       The  nice  value set with setpriority() shall be applied to the process. If the process is
       multi-threaded, the nice value shall affect all system scope threads in the process.

       If more than one process is specified, getpriority() shall return value {NZERO} less  than
       the  lowest  nice  value  pertaining  to any of the specified processes, and setpriority()
       shall set the nice values of all of the specified processes to value+ {NZERO}.

       The default  nice  value  is  {NZERO};  lower  nice  values  shall  cause  more  favorable
       scheduling.  While  the range of valid nice values is [0,{NZERO}*2-1], implementations may
       enforce more restrictive limits.  If value+ {NZERO}  is  less  than  the  system's  lowest
       supported  nice  value,  setpriority()  shall  set  the nice value to the lowest supported
       value; if value+ {NZERO} is greater  than  the  system's  highest  supported  nice  value,
       setpriority() shall set the nice value to the highest supported value.

       Only a process with appropriate privileges can lower its nice value.

       Any  processes  or  threads  using SCHED_FIFO or SCHED_RR shall be unaffected by a call to
       setpriority(). This is not considered an error. A process which  subsequently  reverts  to
       SCHED_OTHER need not have its priority affected by such a setpriority() call.

       The  effect  of  changing  the  nice  value  may  vary depending on the process-scheduling
       algorithm in effect.

       Since getpriority() can return the value -1 on successful completion, it is  necessary  to
       set  errno  to  0 prior to a call to getpriority(). If getpriority() returns the value -1,
       then errno can be checked to see if an error occurred or if the value is a legitimate nice
       value.

RETURN VALUE

       Upon successful completion, getpriority() shall return an integer in the range -{NZERO} to
       {NZERO}-1. Otherwise, -1 shall be returned and errno set to indicate the error.

       Upon successful completion, setpriority() shall return 0; otherwise, -1 shall be  returned
       and errno set to indicate the error.

ERRORS

       The getpriority() and setpriority() functions shall fail if:

       ESRCH  No process could be located using the which and who argument values specified.

       EINVAL The  value  of  the  which  argument  was  not  recognized, or the value of the who
              argument is not a valid process ID, process group ID, or user ID.

       In addition, setpriority() may fail if:

       EPERM  A process was located, but neither the real nor effective user ID of the  executing
              process  match  the  effective  user  ID  of  the process whose nice value is being
              changed.

       EACCES A request was made to change the nice value  to  a  lower  numeric  value  and  the
              current process does not have appropriate privileges.

       The following sections are informative.

EXAMPLES

   Using getpriority()
       The  following example returns the current scheduling priority for the process ID returned
       by the call to getpid().

              #include <sys/resource.h>
              ...
              int which = PRIO_PROCESS;
              id_t pid;
              int ret;

              pid = getpid();
              ret = getpriority(which, pid);

   Using setpriority()
       The following example sets the priority for the current process ID to -20.

              #include <sys/resource.h>
              ...
              int which = PRIO_PROCESS;
              id_t pid;
              int priority = -20;
              int ret;

              pid = getpid();
              ret = setpriority(which, pid, priority);

APPLICATION USAGE

       The getpriority() and setpriority() functions work with an offset nice value  (nice  value
       -{NZERO}).  The  nice  value  is in the range [0,2*{NZERO} -1], while the return value for
       getpriority() and the third parameter for setpriority() are in the range [-{NZERO},{NZERO}
       -1].

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       nice()  , sched_get_priority_max() , sched_setscheduler() , the Base Definitions volume of
       IEEE Std 1003.1-2001, <sys/resource.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2003  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .