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RCMD(3)			RedHat Library Functions Manual		       RCMD(3)

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

     #include <unistd.h>

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

     rresvport(int *port);

     iruserok(u_int32_t	raddr, int superuser, const char *ruser,
	 const char *luser);

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

     The rcmd()	function is used by the	super-user to execute a	command	on a
     remote machine using an authentication scheme based on reserved port num-
     bers.  The	rresvport() function returns a descriptor to a socket with an
     address in	the privileged port space.  The	iruserok() and ruserok() func-
     tions are used by servers to authenticate clients requesting service with
     rcmd().  All four functions are present in	the same file and are used by
     the rshd(8) server	(among others).

     The rcmd()	function looks up the host *ahost using	gethostbyname(3),
     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	com-
     mand (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(8).

     The rresvport() function is used to obtain	a socket with a	privileged
     address bound to it.  This	socket is suitable for use by rcmd() and sev-
     eral other	functions.  Privileged Internet	ports are those	in the range 0
     to	1023.  Only the	super-user is allowed to bind an address of this sort
     to	a socket.

     The iruserok() and	ruserok() functions take a remote host's IP address or
     name, respectively, two user names	and a flag indicating whether the
     local user's name is that of the super-user.  Then, if the	user is	NOT
     the super-user, it	checks the /etc/hosts.equiv file.  If that lookup is
     not done, or is unsuccessful, the .rhosts in the local user's home	direc-
     tory is checked to	see if the request for service is allowed.

     If	this file does not exist, is not a regular file, is owned by anyone
     other than	the user or the	super-user, or is writeable by anyone other
     than the owner, the check automatically fails.  Zero is returned if the
     machine name is listed in the ``hosts.equiv'' file, or the	host and
     remote user name are found	in the ``.rhosts'' file; otherwise iruserok()
     and ruserok() return -1.  If the local domain (as obtained	from
     gethostname(2)) is	the same as the	remote domain, only the	machine	name
     need be specified.

     If	the IP address of the remote host is known, iruserok() should be used
     in	preference to ruserok(), as it does not	require	trusting the DNS
     server for	the remote host's domain.

     The rcmd()	function returns a valid socket	descriptor on success.	It
     returns -1	on error and prints a diagnostic message on the	standard

     The rresvport() function returns a	valid, bound socket descriptor on suc-
     cess.  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.''

     rlogin(1),	rsh(1),	intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)

     These functions appeared in 4.2BSD.

4.2 Berkeley Distribution	 June 4, 1993	     4.2 Berkeley Distribution


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