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mq_getattr — get message queue attributes (REALTIME)
POSIX Real-time Library (librt, -lrt)
mq_getattr(mqd_t mqdes, struct mq_attr *mqstat);
The mq_getattr() system call obtains status information and attributes of
the message queue and the open message queue description associated with
the message queue descriptor.
The mqdes argument specifies a message queue descriptor.
The results are returned in the mq_attr structure referenced by the
Upon return, the following members will have the values associated with
the open message queue description as set when the message queue was
opened and as modified by subsequent mq_setattr() calls: mq_flags.
The following attributes of the message queue will be returned as set at
message queue creation: mq_maxmsg, mq_msgsize.
Upon return, the following members within the mq_attr structure
referenced by the mqstat argument will be set to the current state of the
mq_flags The number of messages currently on the queue.
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
The mq_getattr() system call will fail if:
[EBADF] The mqdes argument is not a valid message queue
mq_open(2), mq_send(2), mq_setattr(2), mq_timedsend(2)
The mq_getattr() system call conforms to IEEE Std 1003.1-2004
Support for POSIX message queues first appeared in FreeBSD 7.0.
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