msgctl

NAME

LIBRARY

SYNOPSIS

DESCRIPTION

struct msqid_ds { 
	struct	ipc_perm msg_perm;	/* msg queue permission bits */ 
	msglen_t msg_cbytes;	/* number of bytes in use on the queue */ 
	msgqnum_t msg_qnum;	/* number of msgs in the queue */ 
	msglen_t msg_qbytes;	/* max # of bytes on the queue */ 
	pid_t	msg_lspid;	/* pid of last msgsnd() */ 
	pid_t	msg_lrpid;	/* pid of last msgrcv() */ 
	time_t	msg_stime;	/* time of last msgsnd() */ 
	time_t	msg_rtime;	/* time of last msgrcv() */ 
	time_t	msg_ctime;	/* time of last msgctl() */ 
};

struct ipc_perm { 
	uid_t		cuid;	/* creator user id */ 
	gid_t		cgid;	/* creator group id */ 
	uid_t		uid;	/* user id */ 
	gid_t		gid;	/* group id */ 
	mode_t		mode;	/* r/w permission */ 
	unsigned short	seq;	/* sequence # (to generate unique ipcid) */ 
	key_t		key;	/* user specified msg/sem/shm key */ 
};

IPC_STAT

Gather information about the message queue and place it in the structure pointed to by buf.

IPC_SET

Set the value of the msg_perm.uid, msg_perm.gid, msg_perm.mode and msg_qbytes fields in the structure associated with msqid. The values are taken from the corresponding fields in the structure pointed to by buf. This operation can only be executed by the super-user, or a process that has an effective user id equal to either msg_perm.cuid or msg_perm.uid in the data structure associated with the message queue. The value of msg_qbytes can only be increased by the super-user. Values for msg_qbytes that exceed the system limit (MSGMNB from <sys/msg.h>) are silently truncated to that limit.

IPC_RMID

Remove the message queue specified by msqid and destroy the data associated with it. Only the super-user or a process with an effective uid equal to the msg_perm.cuid or msg_perm.uid values in the data structure associated with the queue can do this.

RETURN VALUES

ERRORS

[EPERM]

The cmd argument is equal to IPC_SET or IPC_RMID and the caller is not the super-user, nor does the effective uid match either the msg_perm.uid or msg_perm.cuid fields of the data structure associated with the message queue.

An attempt is made to increase the value of msg_qbytes through IPC_SET but the caller is not the super-user.

[EACCES]

The command is IPC_STAT and the caller has no read permission for this message queue.

[EINVAL]

The msqid argument is not a valid message queue identifier.

cmd is not a valid command.

[EFAULT]

The buf argument specifies an invalid address.

SEE ALSO

HISTORY