Provided by: freebsd-manpages_9.2+1-1_all 
NAME
rtprio — examine or modify a process realtime or idle priority
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <sys/rtprio.h>
int
rtprio(int function, pid_t pid, struct rtprio *rtp);
DESCRIPTION
The rtprio() system call is used to lookup or change the realtime or idle priority of a process.
The function argument specifies the operation to be performed. RTP_LOOKUP to lookup the current priority,
and RTP_SET to set the priority. The pid argument specifies the process to be used, 0 for the current
process.
The *rtp argument is a pointer to a struct rtprio which is used to specify the priority and priority type.
This structure has the following form:
struct rtprio {
u_short type;
u_short prio;
};
The value of the type field may be RTP_PRIO_REALTIME for realtime priorities, RTP_PRIO_NORMAL for normal
priorities, and RTP_PRIO_IDLE for idle priorities. The priority specified by the prio field ranges between
0 and RTP_PRIO_MAX (usually 31). 0 is the highest possible priority.
Realtime and idle priority is inherited through fork() and exec().
A realtime process can only be preempted by a process of equal or higher priority, or by an interrupt; idle
priority processes will run only when no other real/normal priority process is runnable. Higher real/idle
priority processes preempt lower real/idle priority processes. Processes of equal real/idle priority are
run round-robin.
RETURN VALUES
The rtprio() function returns the value 0 if successful; otherwise the value -1 is returned and the global
variable errno is set to indicate the error.
ERRORS
The rtprio() system call will fail if:
[EINVAL] The specified prio was out of range.
[EPERM] The calling process is not allowed to set the realtime priority. Only root is allowed
to change the realtime priority of any process, and non-root may only change the idle
priority of the current process.
[ESRCH] The specified process was not found.
SEE ALSO
nice(1), ps(1), rtprio(1), setpriority(2), nice(3), renice(8)
AUTHORS
The original author was Henrik Vestergaard Draboel <hvd@terry.ping.dk>. This implementation in FreeBSD was substantially rewritten by David Greenman.