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 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 the value of msgperm.cuid or
                 msgperm.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
     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.





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msgctl(2)                                                            msgctl(2)



     EINVAL         cmd is not a valid command.

     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 equal to the value of msgperm.cuid
                    or msgperm.uid in the data structure associated with
                    msqid and the process does not have the super-user
                    privilege.

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