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 are created for key if one of the following is true:

key is equal to IPC_PRIVATE.  This call creates a new identifier, subject to available resources.  The identifier will never be returned by another call to msgget() until it has been released by a call to msgctl().  The identifier should be used among the calling process and its descendents; however, it is not a requirement.  The resource can be accessed by any process having the proper permissions. 

key does not already have a message queue identifier associated with it, and (msgflg & IPC_CREAT) is “true”. 

Upon 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 equal 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 equal to the low-order 9 bits of msgflg.

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

msg_ctime is set equal to the current time. 

msg_qbytes is set equal to the system limit. 

RETURN VALUE

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

ERRORS

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

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

[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. 

[EEXIST] A message queue identifier exists for key but ((msgflg & IPC_CREAT) && (msgflg & IPC_EXCL)) is “true”.

SEE ALSO

ipcrm(1), ipcs(1), msgctl(2), msgop(2), stdipc(3C). 

STANDARDS CONFORMANCE

msgget(): SVID2, XPG2, XPG3, XPG4

Hewlett-Packard Company  —  HP-UX Release 9.0: August 1992