msgget(2)

NAME

msgget − get message queue

SYNOPSIS

#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 and associated message queue and data structure (see intro(2)) are created for key if one of the following are true:

• key is IPC_PRIVATE.

• 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 message queue identifier is initialized as follows:

• 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 process.

• The low-order 9 bits of msg_perm.mode are set to the low-order 9 bits of msgflg.

• msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set to 0.

• msg_ctime is set to the current time.

• msg_qbytes is set to the system limit.

RETURN VALUES

Upon successful completion, a non-negative integer, namely a message queue identifier, is returned. Otherwise, −1 is returned and errno is set to indicate the error.

ERRORS

msgget() fails if one or more of the following are true:

EACCES A message queue identifier exists for key, but operation permission (see intro(2)) as specified by the low-order 9 bits of msgflg would not be granted.

EEXIST A message queue identifier exists for key but (msgflg&IPC_CREAT) and (msgflg&IPC_EXCL) are both true.

ENOENT A message queue identifier does not exist for key and (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.

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