NAME
msgget —
get message queue
SYNOPSIS
#include
<sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int
msgget(key_t
key, int
msgflg);
DESCRIPTION
msgget()
returns the message queue identifier associated with
key. A message queue identifier is a unique integer
greater than zero.
A message queue is created if either key is
equal to IPC_PRIVATE, or key
does not have a message queue identifier associated with it, and the
IPC_CREAT bit is set in
msgflg.
If a new message queue is created, the data structure associated with it (the msqid_ds structure, see msgctl(2)) is initialized as follows:
- msg_perm.cuid and msg_perm.uid are set to the effective UID of the calling process.
- msg_perm.gid and msg_perm.cgid are set to the effective GID of the calling process.
- msg_perm.mode is set to the lower 9 bits of msgflg.
- msg_cbytes, msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime are set to 0.
- msg_qbytes is set to the system wide
maximum value for the number of bytes in a queue
(
MSGMNB). - msg_ctime is set to the current time.
RETURN VALUES
Upon successful completion a positive message queue identifier is returned. Otherwise, -1 is returned and the global variable errno is set to indicate the error.
ERRORS
- [
EACCES] - A message queue is already associated with key and the caller has no permission to access it.
- [
EEXIST] - Both
IPC_CREATandIPC_EXCLare set in msgflg, and a message queue is already associated with key. - [
ENOSPC] - A new message queue could not be created because the system limit for the number of message queues has been reached.
- [
ENOENT] IPC_CREATwas not set in msgflg and no message queue associated with key was found.
SEE ALSO
HISTORY
Message queues appeared in the first release of AT&T Unix System V.