2.11BSD#431 - /usr/man/cat3/rresvport.0

RCMD(3)             UNIX Programmer's Manual		  RCMD(3)


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

SYNOPSIS
     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 com-
     mand 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(8C) server (among others).

     Rcmd looks up the host *ahost using gethostbyname(3N),
     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 for-
     warded 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(8C).


Printed 11/26/99	  May 14, 1986				1


RCMD(3)             UNIX Programmer's Manual		  RCMD(3)


     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(3N) routine, two user names and a flag indi-
     cating whether the local user's name is that of the super-
     user.  It then checks the files /etc/hosts.equiv and, possi-
     bly, .rhosts in the current working directory (normally the
     local user's home directory) to see if the request for ser-
     vice 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 check-
     ing of the ``host.equiv'' file is bypassed.  If the local
     domain (as obtained from gethostname(2)) is the same as the
     remote domain, only the machine name need be specified.

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

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 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.''


Printed 11/26/99	  May 14, 1986				2