---
name: "mq_setattr"
section: "2"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/mq_setattr"
---

# mq\_setattr(2)

set message queue attributes (REALTIME)

## NAME

**mq\_setattr** – set message queue attributes (REALTIME)

## LIBRARY

library “librt”

## SYNOPSIS

**#include \<mqueue.h\>**

*int*\

**mq\_setattr**(*mqd\_t mqdes*, *const struct mq\_attr \*restrict mqstat*, *struct mq\_attr \*restrict omqstat*);

## DESCRIPTION

The **mq\_setattr**() system call sets attributes associated with the open message queue description referenced by the message queue descriptor specified by *mqdes*. The message queue attributes corresponding to the following members defined in the *mq\_attr* structure will be set to the specified values upon successful completion of **mq\_setattr**():

- *mq\_flags*

  The value of this member is zero or O\_NONBLOCK.

The values of the *mq\_maxmsg*, *mq\_msgsize*, and *mq\_curmsgs* members of the *mq\_attr* structure are ignored by **mq\_setattr**().

## RETURN VALUES

Upon successful completion, the function returns a value of zero and the attributes of the message queue will have been changed as specified.

Otherwise, the message queue attributes are unchanged, and the function returns a value of -1 and sets the global variable *errno* to indicate the error.

## ERRORS

The **mq\_setattr**() system call will fail if:

- \[EBADF\]

  The *mqdes* argument is not a valid message queue descriptor.

## SEE ALSO

[mq\_open(2)](/mq_open/2.md), [mq\_send(2)](/mq_send/2.md), [mq\_timedsend(2)](/mq_timedsend/2.md)

## STANDARDS

The **mq\_setattr**() system call conforms to IEEE Std 1003.1-2004 (“POSIX.1”).

## HISTORY

Support for POSIX message queues first appeared in FreeBSD 7.0.

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.  The original Standard can be obtained online at http://www.opengroup.org/unix/online.html.