# rcmd(3)

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

    SYNOPSIS
         #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;

    DESCRIPTION
         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.

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

    DIAGNOSTICS
         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.''