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RTPRIO(2) FreeBSD System Calls Manual RTPRIO(2)
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 prior-
ity. The pid argument specifies the process to be used, 0 for the cur-
rent process.
The *rtp argument is a pointer to a struct rtprio which is used to spec-
ify 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 priori-
ties, 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 pri-
ority 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.
FreeBSD 6.2 July 23, 1994 FreeBSD 6.2
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This page was generated on Wed Sep 19 20:03:52 BST 2007
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