msgctl(S)

msgctl -- message control operations

Synopsis

   #include <sys/types.h>
   #include <sys/ipc.h>
   #include <sys/msg.h>
   
   int msgctl(int msqid, int cmd, .../ struct msqid_ds buf /);

Description

msgctl provides a variety of message control operations as specified by cmd. The following cmds are available:

IPC_STAT

Place the current value of each member of the data structure associated with msqid into the structure pointed to by buf. The contents of this structure are defined in intro.

IPC_SET

Set the value of the following members of the data structure associated with msqid to the corresponding value found in the structure pointed to by buf:

   msg_perm.uid
   msg_perm.gid
   msg_perm.mode / only access permission bits /
   msg_qbytes

This cmd can only be executed by a process that has an effective user ID equal to the value of msg_perm.cuid or msg_perm.uid in the data structure associated with msqid, or by a process that has the P_OWNER privilege.

IPC_RMID

Remove the message queue identifier specified by msqid from the system and destroy the message queue and data structure associated with it. This cmd can only be executed by a process that has an effective user ID equal to the value of msg_perm.cuid or msg_perm.uid in the data structure associated with msqid, or by a process that has the P_OWNER privilege.

Return values

On success, msgctl returns 0. On failure, msgctl returns -1 and sets errno to identify the error.

Errors

In the following conditions, msgctl fails and sets errno to:

EACCES: cmd is IPC_STAT and operation permission is denied to the calling process [see intro(S)].
EFAULT: buf points to an illegal address.
EINVAL: msqid is not a valid message queue identifier.
EINVAL: cmd is not a valid command.
EINVAL: cmd is IPC_SET and msg_perm.uid or msg_perm.gid is not valid.
EOVERFLOW: cmd is IPC_STAT and uid or gid is too large to be stored in the structure pointed to by buf.
EPERM: cmd is IPC_RMID or IPC_SET, the effective user ID of the calling process is not equal to the value of msg_perm.cuid or msg_perm.uid in the data structure associated with msqid and the process does not have the P_OWNER privilege.

References

intro(S), msgget(S), msgop(S)