Provided by: freebsd-manpages_12.2-2_all 
NAME
msgget — get message queue
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/msg.h>
int
msgget(key_t key, int msgflg);
DESCRIPTION
The msgget() function 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 which are set by ORing these constants:
0400
Read access for user.
0200
Write access for user.
0040
Read access for group.
0020
Write access for group.
0004
Read access for other.
0002
Write access for other.
• 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_CREAT and IPC_EXCL are 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_CREAT was not set in msgflg and no message queue associated with key was found.
SEE ALSO
msgctl(2), msgrcv(2), msgsnd(2)
HISTORY
Message queues appeared in the first release of AT&T System V UNIX.