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

NAME

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

SYNOPSIS

     #include <unistd.h>

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

     int
     rresvport(int *port);

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

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

DESCRIPTION

     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
     numbers.  The rresvport() function returns a descriptor to a socket with an address in the privileged port space.	The iruserok() and
     ruserok() functions 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 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(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
     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 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 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.

DIAGNOSTICS

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

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

SEE ALSO

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

HISTORY

     These functions appeared in 4.2BSD.

4.2 Berkeley Distribution					   June 4, 1993 					 4.2 Berkeley Distribution