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RCMD(3)			 BSD Library Functions Manual		       RCMD(3)

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

     Standard C	Library	(libc, -lc)

     #include <unistd.h>

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

     rresvport(int *port);

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

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

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

     rresvport_af(int *port, int af);

     iruserok_sa(const void *addr, int addrlen,	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	ruserok() function is 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(8)
     server (among others).

     The rcmd()	function looks up the host *ahost using	gethostbyname(3), re-
     turning -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 re-
     siding 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 to which an address
     with a Privileged Internet	port is	bound.	This socket is suitable	for
     use by rcmd() and several 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, as returned by the gethostbyname(3) routines, 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 directory 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 writable 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(3)) is	the same as the	remote domain, only the	machine	name
     need be specified.

     The iruserok() function is	strongly preferred for security	reasons.  It
     requires trusting the local DNS at	most, while the	ruserok() function re-
     quires trusting the entire	DNS, which can be spoofed.

     The functions with	an "_af" or "_sa" suffix, i.e.,	rcmd_af(),
     rresvport_af() and	iruserok_sa(), work the	same as	the corresponding
     functions without a suffix, except	that they are capable of handling both
     IPv6 and IPv4 ports.

     The "_af" suffix means that the function has an additional	af argument
     which is used to specify the address family, (see below).	The af argu-
     ment extension is implemented for functions that have no binary address
     argument.	Instead, the af	argument specifies which address family	is de-

     The "_sa" suffix means that the function has general socket address and
     length arguments.	As the socket address is a protocol independent	data
     structure,	IPv4 and IPv6 socket address can be passed as desired.	The sa
     argument extension	is implemented for functions that pass a protocol de-
     pendent binary address argument.  The argument needs to be	replaced with
     a more general address structure to support multiple address families in
     a general way.

     The functions with	neither	an "_af" suffix	nor an "_sa" suffix work for
     IPv4 only,	except for ruserok() which can handle both IPv6	and IPv4.  To
     switch the	address	family,	the af argument	must be	filled with AF_INET,
     or	AF_INET6.  For rcmd_af(), PF_UNSPEC is also allowed.

     RSH  When using the rcmd()	function, this variable	is used	as the program
	  to run instead of rsh(1).

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

     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), rlogind(8), rshd(8)

     W.	Stevens	and M. Thomas, Advanced	Socket API for IPv6, RFC2292.

     W.	Stevens, M. Thomas, and	E. Nordmark, Advanced Socket API for IPv6,

     Most of these functions appeared in 4.2BSD.  The rresvport_af() function
     appeared in RFC2292, and was implemented by the WIDE project for the Hy-
     drangea IPv6 protocol stack kit.  The rcmd_af() function appeared in
     draft-ietf-ipngwg-rfc2292bis-01.txt, and was implemented in the WIDE/KAME
     IPv6 protocol stack kit.  The iruserok_sa() function appeared in discus-
     sion on the IETF ipngwg mailing list, and was implemented in FreeBSD 4.0.

BSD				 March 3, 2000				   BSD


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