MSGGET

Section: System Calls (2)
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BSD mandoc
NetBSD

NAME

msgget - get message queue

SYNOPSIS

Fd #include <sys/types.h> Fd #include <sys/ipc.h> Fd #include <sys/msg.h> Ft int Fn msgget key_t key int msgflg

DESCRIPTION

Fn msgget returns the message queue identifier associated with Fa key . A message queue identifier is a unique integer greater than zero.

A message queue is created if either Fa key is equal to IPC_PRIVATE, or Fa key does not have a message queue identifier associated with it, and the IPC_CREAT bit is set in Fa msgflg.

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 Fa msgflg .
msg_cbytes 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.

RETURN VALUES

Upon successful completion a positive message queue identifier is returned. Otherwise, -1 is returned and the global variable errno is set to indicate the error.

ERRORS

Bq Er EACESS: A message queue is already associated with Fa key and the caller has no permission to access it.
Bq Er EEXIST: Both IPC_CREAT and IPC_EXCL are set in Fa msgflg , and a message queue is already associated with Fa key .
Bq Er ENOSPC: A new message queue could not be created because the system limit for the number of message queues has been reached.
Bq Er ENOENT: IPC_CREAT was not set in Fa msgflg and no message queue associated with Fa key was found.

HISTORY

Message queues appeared in the first release of AT&T Unix System V.

This document was created by man2html, using the manual pages.
Time: 16:28:59 GMT, April 18, 2022