RCMD(3N)							      RCMD(3N)

NAME    [Toc]    [Back]

     rcmd, rresvport, ruserok -	routines for returning a stream	to a remote
     command

SYNOPSIS    [Toc]    [Back]

     rcmd(char **ahost,	u_short	inport,	char *locuser, char *remuser,
	       char *cmd, int *fd2p);

     rresvport(int *port);

     ruserok(char *rhost, int superuser, char *ruser, char *luser);

DESCRIPTION    [Toc]    [Back]

     Rcmd is a routine used by the super-user to execute a command on a	remote
     machine using an authentication scheme based on reserved port numbers.
     Rresvport is a routine which returns a descriptor to a socket with	an
     address in	the privileged port space.  Ruserok is a routine used by
     servers to	authenticate clients requesting	service	with rcmd.  All	three
     functions are present in the same file and	are used by the	rshd(1M)
     server (among others).

     Rcmd looks	up the host *ahost using gethostbyname(3N), returning -1 if
     the host does not exist.  Otherwise *ahost	is set to the standard name of
     the host and a connection is established to a server residing at the
     well-known	Internet port inport.

     If	the connection succeeds, a socket in the Internet domain of type
     SOCK_STREAM is returned to	the caller, and	given to the remote command as
     stdin and stdout.	If fd2p	is non-zero, then an auxiliary channel to a
     control process will be set up, and a descriptor for it will be placed in
     *fd2p.  The control process will return diagnostic	output from the
     command (unit 2) on this channel, and will	also accept bytes on this
     channel as	being UNIX signal numbers, to be forwarded to the process
     group of the command.  If fd2p is 0, then the stderr (unit	2 of the
     remote command) will be made the same as the stdout and no	provision is
     made for sending arbitrary	signals	to the remote process, although	you
     may be able to get	its attention by using out-of-band data.

     The protocol is described in detail in rshd(1M).

     The rresvport routine is used to obtain a socket with a privileged
     address bound to it.  This	socket is suitable for use by rcmd and several
     other routines.  Privileged Internet ports	are those in the range 512 to
     1023.  Only the super-user	is allowed to bind an address of this sort to
     a socket.

     Ruserok takes a remote host's name, as returned by	a gethostbyaddr(3N)
     routine, two user names and a flag	indicating whether the local user's
     name is that of the super-user.  It then checks the files
     /etc/hosts.equiv and, possibly, .rhosts in	the local user's home
     directory to see if the request for service is allowed.  A	0 is returned
     if	the machine name is listed in the ``hosts.equiv'' file,	or the host



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RCMD(3N)							      RCMD(3N)



     and remote	user name are found in the ``.rhosts'' file; otherwise ruserok
     returns -1.  If the superuser flag	is 1, the checking of the
     ``hosts.equiv'' file is bypassed.	If the local domain (as	obtained from
     gethostname(2)) is	the same as the	remote domain, only the	machine	name
     need be specified.

SEE ALSO    [Toc]    [Back]

     rlogin(1C), rsh(1C), intro(2), rexec(3N), rexecd(1M), rlogind(1M),
     rshd(1M)

DIAGNOSTICS    [Toc]    [Back]

     Rcmd returns a valid socket descriptor on success.	 It returns -1 on
     error and prints a	diagnostic message on the standard error.

     Rresvport returns a valid,	bound socket descriptor	on success.  It
     returns -1	on error with the global value errno set according to the
     reason for	failure.  The error code EAGAIN	is overloaded to mean ``All
     network ports in use.''


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