rtprio(2)

NAME

Standard C Library (libc, -lc)

#include <sys/types.h>
#include <sys/rtprio.h>
int
rtprio(int function, pid_t pid, struct rtprio *rtp);

The rtprio() system call is used to lookup or change the re
altime or idle priority of a process.
The function argument specifies the operation to be per
formed. 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 re
altime 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.

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.