MSGCTL(2)                            SysV                            MSGCTL(2)



NAME
     msgctl - message control operations

SYNOPSIS
     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/msg.h>

     int msgctl (msqid, cmd, buf)
     int msqid, 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).  {READ}

     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 low 9 bits */
               msg_qbytes

               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.  Only super user 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.

ERRORS
     msgctl will fail if one or more of the following are true:

     [EINVAL]   msqid is not a valid message queue identifier.

     [EINVAL]   cmd is not a valid command.

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

     [EPERM]    cmd is equal to IPC_RMID or IPC_SET.  The effective user ID of
                the calling process is not equal to that of super-user or to
                the value of msg_perm.cuid or msg_perm.uid in the data
                structure associated with msqid.

     [EPERM]    cmd is equal to IPC_SET, an attempt is being made to increase
                to the value of msg_qbytes, and the effective user ID of the
                calling process is not equal to that of super user.

     [EFAULT]   buf points to an illegal address.

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.