The
msgget() system call 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 both the
IPC_CREAT bit and the
IPC_EXCL bit are set in
msgflg, and
key has a message queue identifier associated with it already, the operation will fail.
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_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.