System Calls msgget(2)
msgget - get message queue
int msgget(key_t key, int msgflg);
The msgget() argument returns the message queue identifier
associated with key.
A message queue identifier and associated message queue and
data structure (see intro(2)) are created for key if one of
the following are true:
o key is IPC_PRIVATE.
o key does not already have a message queue identifier
associated with it, and (msgflg&IPC_CREAT) is true.
On creation, the data structure associated with the new mes-
sage queue identifier is initialized as follows:
o msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and
msg_perm.gid are set to the effective user ID and
effective group ID, respectively, of the calling pro-
o The low-order 9 bits of msg_perm.mode are set to the
low-order 9 bits of msgflg.
o msg_qnum, msg_lspid, msg_lrpid, msg_stime, and
msg_rtime are set to 0.
o msg_ctime is set to the current time.
o msg_qbytes is set to the system limit.
Upon successful completion, a non-negative integer
representing a message queue identifier is returned. Other-
wise, -1 is returned and errno is set to indicate the error.
The msgget() function will fail if:
A message queue identifier exists for key, but opera-
tion permission (see intro(2)) as specified by the
low-order 9 bits of msgflg would not be granted.
SunOS 5.9 Last change: 5 Feb 1996 1
System Calls msgget(2)
A message queue identifier exists for key but
(msgflg&IPC_CREAT) and (msgflg&IPC_EXCL) are both
A message queue identifier does not exist for key and
(msgflg&IPC_CREAT) is false.
A message queue identifier is to be created but the
system-imposed limit on the maximum number of allowed
message queue identifiers system wide would be
When a UFS file system is mounted with logging enabled, file
system transactions that free blocks from files might not
actually add those freed blocks to the file system's free
list until some unspecified time in the future. This
behavior improves file system performance but does not con-
form to the POSIX, Single UNIX Specification, SPARC Confor-
mance Definition, System V Application Binary Interface,
System V Interface Definition, and X/Open Portability Guide
Standards, which require that freed space be available
immediately. To enable standards conformance regarding file
deletions or to address the problem of not being able to
grow files on a relatively full UFS file system even after
files have been deleted, disable UFS logging (see
mount_ufs(1M), intro(2), msgctl(2), msgrcv(2), msgsnd(2),
SunOS 5.9 Last change: 5 Feb 1996 2