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 msqidds *buf */);

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

      IPCSTAT    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).

      IPCSET     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:
                        msgperm.uid
                        msgperm.gid
                        msgperm.mode /* only access permission bits */
                        msgqbytes

                  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 msgperm.cuid or msgperm.uid in the data
                  structure associated with msqid.  Only super user can raise
                  the value of msgqbytes.

      IPCRMID    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 msgperm.cuid or msgperm.uid
                  in the data structure associated with msqid.

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

      EACCES         cmd is IPCSTAT 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 IPCSET and msgperm.uid or msgperm.gid is not
                     valid.

      EOVERFLOW      cmd is IPCSTAT and uid or gid is too large to be stored
                     in the structure pointed to by buf.

      EPERM          cmd is IPCRMID or IPCSET.  The effective user ID of the
                     calling process is not that of super user, or the value of
                     msgperm.cuid or msgperm.uid in the data structure
                     associated with msqid.

      EPERM          cmd is IPCSET, an attempt is being made to increase to
                     the value of msgqbytes, 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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