GETPRIORITY(2)                System Calls Manual               GETPRIORITY(2)

NAME
     getpriority, setpriority – get/set program scheduling priority

SYNOPSIS
     #include <sys/resource.h>

     int
     getpriority(int which, id_t who);

     int
     setpriority(int which, id_t who, int prio);

DESCRIPTION
     The scheduling priority of the process, process group, or user as
     indicated by which and who is obtained with the getpriority() call and
     set with the setpriority() call.  Which is one of PRIO_PROCESS,
     PRIO_PGRP, or PRIO_USER, and who is interpreted relative to which (a
     process identifier for PRIO_PROCESS, process group identifier for
     PRIO_PGRP, and a user ID for PRIO_USER).  A zero value of who denotes the
     current process, process group, or user.  prio is a value in the range
     -20 to 20.  The default priority is 0; lower priorities cause more
     favorable scheduling.

     The getpriority() call returns the highest priority (lowest numerical
     value) enjoyed by any of the specified processes.  The setpriority() call
     sets the priorities of all of the specified processes to the specified
     value.  Only the super-user may lower priorities.

     Additionally, the current thread or process can be placed in a background
     state by specifying PRIO_DARWIN_THREAD or PRIO_DARWIN_PROCESS for which.
     Only a value of zero (the current thread or process) is supported for who
     when setting or getting background state.  prio is either 0 (to remove
     current thread from background status) or PRIO_DARWIN_BG (to set current
     thread into background state).  When a thread or process is in a
     background state the scheduling priority is set to the lowest value, disk
     IO is throttled (with behavior similar to using setiopolicy_np(3) to set
     a throttleable policy), and network IO is throttled for any sockets
     opened after going into background state.  Any previously opened sockets
     are not affected.  The getpriority() call returns 0 when current thread
     or process is not in background state or 1 when the current thread is in
     background state.  Any thread or process can set itself into background
     state.

RETURN VALUES
     Since getpriority() can legitimately return the value -1, it is necessary
     to clear the external variable errno prior to the call, then check it
     afterward to determine if a -1 is an error or a legitimate value.  The
     setpriority() call returns 0 if there is no error, or -1 if there is.

ERRORS
     getpriority() and setpriority() will fail if:

     [EINVAL]           Which is not one of PRIO_PROCESS, PRIO_PGRP,
                        PRIO_USER, PRIO_DARWIN_THREAD, or PRIO_DARWIN_PROCESS.

     [EINVAL]           Who is not a valid process, process group, or user ID.

     [EINVAL]           Who is not 0 when which is PRIO_DARWIN_THREAD or
                        PRIO_DARWIN_PROCESS.

     [ESRCH]            No process can be located using the which and who
                        values specified.

     In addition to the errors indicated above, setpriority() will fail if:

     [EACCES]           A non super-user attempts to lower a process priority.

     [EPERM]            A process is located, but neither its effective nor
                        real user ID matches the effective user ID of the
                        caller.

LEGACY SYNOPSIS
     #include <sys/types.h>
     #include <sys/resource.h>

     The include file <sys/types.h> is necessary.

     int
     getpriority(int which, int who);

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

     The type of who has changed.

SEE ALSO
     nice(1), fork(2), setiopolicy_np(3), compat(5), renice(8)

HISTORY
     The getpriority() function call appeared in 4.2BSD.

BSD 4                            June 4, 1993                            BSD 4