msgget(2)msgget(2)Namemsgget - get message queue
Syntax
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int msgget (key, msgflg)
key_t key;
int msgflg;
Description
The system call returns the message queue identifier associated with
key.
A message queue identifier and associated message queue and data struc‐
ture are created for key if one of the following is true:
· The key is equal to IPC_PRIVATE
· The key does not already have a message queue identifier associ‐
ated with it, and (msgflg & IPC_CREAT) is true. For further
information, see
Upon creation, the data structure associated with the new message queue
identifier is initialized as follows:
· The msg_perm.cuid, msg_perm.uid, msg_perm.cgid and msg_perm.gid
members are set equal to the effective user ID and effective group
ID, respectively, of the calling process.
· The low-order nine bits of msg_perm.mode are set equal to the low-
order nine bits of msgflg.
· The msg_qnum, msg_lspid, msg_lrpid, msg_stime, and mgs_rtime mem‐
bers are set equal to 0.
· The msg_ctime is set equal to the current time.
· The msg_qbytes is set equal to the system limit.
Return Values
Upon successful completion, a non-negative integer, which is a message
queue identifier, is returned. Otherwise, a value of -1 is returned,
and errno is set to indicate the error.
Diagnostics
The system call fails under the following conditions:
[EACCES] A message queue identifier exists for key but operations
permission, as specified by the low-order nine bits of
msgflg, would not be granted. For further information,
see
[ENOENT] A message queue identifier does not exist for key and
the logical operation (msgflg & IPC_CREAT) is false.
[ENOSPC] 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 exceeded.
[EEXIST] A message queue identifier exists for key but the logi‐
cal operation ((msgflg & IPC_CREAT ) & (msgflg &
IPC_EXCL )) is true.
See Alsomsgctl(2), msgop(2), ftok(3)msgget(2)
