---
name: "rtprio"
section: "2"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/rtprio/2"
---

# rtprio(2)

examine or modify a process realtime or idle priority

## 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)](/nice/1.md), [ps(1)](/ps/1.md), [rtprio(1)](/rtprio/1.md), [setpriority(2)](/setpriority/2.md), [nice(3)](/nice/3.md), [renice(8)](/renice/8.md)

## AUTHORS

The original author was Henrik Vestergaard Draboel ⟨hvd@terry.ping.dk⟩. This implementation in FreeBSD was substantially rewritten by David Greenman.