msgctl(2)                                                            msgctl(2)


NAME
     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(2).

     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 super-user privilege.

     A process with the super-user privilege can raise the value of
     msg_qbytes.

     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 either that of super user, or to the
          value of msg_perm.cuid or msg_perm.uid in the data structure
          associated with msqid.

     msgctl fails if one or more of the following are true:

     EACCES         cmd is IPC_STAT and operation permission is denied to the
                    calling process [see intro(2)].

     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 super-user
                    privilege.

     EPERM          cmd is IPC_SET, an attempt is being made to increase to
                    the value of msg_qbytes, and the calling process does not
                    have the super-user privilege.

SEE ALSO
     intro(2), msgget(2), msgop(2).

DIAGNOSTICS
     Upon successful completion, a value of 0 is returned. Otherwise, a value
     of -1 is returned and errno is set to indicate the error.


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