---
name: "rtprio"
section: "2freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "12.2-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/rtprio/2freebsd"
---

# rtprio(2freebsd)

examine or modify realtime or idle priority

## NAME

**rtprio**, **rtprio\_thread** – examine or modify 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*);

*int*\

**rtprio\_thread**(*int function*, *lwpid\_t lwpid*, *struct rtprio \*rtp*);

## DESCRIPTION

The **rtprio**() system call is used to lookup or change the realtime or idle priority of a process, or the calling thread. The **rtprio\_thread**() system call is used to lookup or change the realtime or idle priority of a thread.

The *function* argument specifies the operation to be performed. RTP\_LOOKUP to lookup the current priority, and RTP\_SET to set the priority.

For the **rtprio**() system call, the *pid* argument specifies the process to operate on, 0 for the calling thread. When *pid* is non-zero, the system call reports the highest priority in the process, or sets all threads' priority in the process, depending on value of the *function* argument.

For the **rtprio\_thread**() system call, the *lwpid* specifies the thread to operate on, 0 for the calling thread.

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 thread can only be preempted by a thread of equal or higher priority, or by an interrupt; idle priority threads will run only when no other real/normal priority thread is runnable. Higher real/idle priority threads preempt lower real/idle priority threads. Threads of equal real/idle priority are run round-robin.

## RETURN VALUES

The **rtprio()** and **rtprio\_thread()** functions return 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**() and **rtprio\_thread**() system calls will fail if:

- \[EFAULT\]

  The rtp pointer passed to **rtprio**() or **rtprio\_thread**() was invalid.

- \[EINVAL\]

  The specified *prio* was out of range.

- \[EPERM\]

  The calling thread is not allowed to set the realtime priority. Only root is allowed to change the realtime priority of any thread, and non-root may only change the idle priority of threads the user owns, when the [sysctl(8)](/sysctl/8.md) variable *security.bsd.unprivileged\_idprio* is set to non-zero.

- \[ESRCH\]

  The specified process or thread was not found or visible.

## 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), [p\_cansee(9)](/p_cansee/9.md)

## AUTHORS

The original author was Henrik Vestergaard Draboel ⟨*hvd@terry.ping.dk*⟩. This implementation in FreeBSD was substantially rewritten by David Greenman. The **rtprio\_thread**() system call was implemented by David Xu.