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

     #include <sys/types.h>
     #include <net/netlib.h>

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

     s = rresvport(port); int *port;

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

     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(8) server
     (among others).

     Rcmd 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 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  0  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(3)
     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 current working directory
     (normally 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 and remote user name are found  in  the
     ``.rhosts'' file; otherwise ruserok returns -1.  If the superuser flag is
     1, the checking of the ``host.equiv'' file is  bypassed.   If  the  local
     domain  (as  obtained  from  gethostname(3))  is  the  same as the remote
     domain, only the machine name need be specified.

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

     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.''