msgctl(2)                        UNIX System V                        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 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.

      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.





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msgctl(2)                        UNIX System V                        msgctl(2)


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

      EPERM          cmd is 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 that of super user.

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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