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

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

     Standard C	Library	(libc, -lc)

     #include <unistd.h>

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

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

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

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

     rresvport(int *port);

     rresvport_af(int *port, int family);

     iruserok(uint32_t raddr, int superuser, const char	*ruser,
	 const char *luser);

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

     iruserok_sa(const void *raddr, int	rlen, int superuser,
	 const char *ruser, const char *luser);

     The rcmd()	function is available for use by anyone	to run commands	on a
     remote system.  It	acts like the orcmd() command, with the	exception that
     it	makes a	call out to the	rcmd(1)	command, or any	other user-specified
     command, to perform the actual connection (thus not requiring that	the
     caller be running as the super-user), and is only available for the
     "shell/tcp" port.	The orcmd() function is	used by	the super-user to exe-
     cute a command on a remote	machine	using an authentication	scheme based
     on	reserved port numbers.	While rcmd() and orcmd() can only handle IPv4
     address in	the first argument, rcmd_af() and orcmd_af() can handle	other
     cases as well.  The rresvport() function returns a	descriptor to a	socket
     with an address in	the privileged port space.  The	rresvport_af() func-
     tion is similar to	rresvport(), but you can explicitly specify the	ad-
     dress family to use.  Calling rresvport_af() with AF_INET has the same
     effect as rresvport().  The iruserok() and	ruserok() functions are	used
     by	servers	to authenticate	clients	requesting service with	rcmd().	 All
     six functions are present in the same file	and are	used by	the rshd(8)
     server (among others).  iruserok_sa() is an address family	independent
     variant of	iruserok().

     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.

     rcmd_af() and orcmd_af() take address family in the last argument.	 If
     the last argument is PF_UNSPEC, interpretation of *ahost will obey	the
     underlying	address	resolution like	DNS.

     The protocol is described in detail in rshd(8).

     The rresvport() and rresvport_af()	functions are used to obtain a socket
     with a privileged address bound to	it.  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, respectively, two user names	and a flag indicating whether the lo-
     cal 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.

     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.

     While iruserok() can handle IPv4 addresses	only, iruserok_sa() and
     ruserok() can handle other	address	families as well, like IPv6.  The
     first argument of iruserok_sa() is	typed as void *	to avoid dependency
     between <unistd.h>	and <sys/socket.h>.

     RCMD_CMD	 When using the	rcmd() function, this variable is used as the
		 program to run	instead	of rcmd(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() and rresvport_af()	function return	a valid, bound socket
     descriptor	on success.  They return -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.''

     rcmd(1), rlogin(1), rsh(1), intro(2), rexec(3), hosts.equiv(5),
     rhosts(5),	rexecd(8), rlogind(8), rshd(8)

     The orcmd(), rresvport(), iruserok() and ruserok()	functions appeared in
     4.2BSD, where the orcmd() function	was called rcmd().  The	(newer)	rcmd()
     function appeared in NetBSD 1.3.  rcmd_af() and rresvport_af() were de-
     fined in RFC2292.

BSD				March 30, 2005				   BSD


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