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msgget.2freebsd

BSD mandoc

NAME

msgget - get message queue

LIBRARY

Lb libc

SYNOPSIS

In sys/types.h In sys/ipc.h In sys/msg.h Ft int Fn msgget key_t key int msgflg

DESCRIPTION

The Fn msgget function 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 EACCES

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.

SEE ALSO

msgctl(2), msgrcv(2), msgsnd(2)

HISTORY

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