how do I handle ssh response with expect Post: 302221525

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Top Forums Shell Programming and Scripting how do I handle ssh response with expect Post 302221525 by buffoonix on Monday 4th of August 2008 04:12:17 PM

08-04-2008

Registered User

Hi,

I haven't read your Expect script because it's been far too long since I last wrote anything in Tcl.
Anyway, I think there is no real need for any sophisticated Expect prompting logic here
since the warning you encounter from your SSH client about an unknown host identity
can be easily circumvented.
If your SSH client connects to a remote SSH server whose host identity it cannot verify,
either because it is the first connect to this host, or maybe the remote host's SSH server was started with different host keys meanwhile (maybe its admin updated SSH and neglected restoring its host key) it will warn you as long as StrictHostKeyChecking isn't set to "no" (per default it is set to "ask", see man ssh_config).
If it is the first connect and you have verified that the presented fingerprint of the remote host key is correct (or you trust it anyway) you simply need to confirm this warning with yes.
Your SSH client will then create a file $HOME/.ssh/known_hosts (if it hasn't existed yet)
and append the public host key offered from the remote SSH server to it.
From then on it will never again ask you as long as the host key on the remote server or the entry in your local known_hosts file for that host will not change.
In that respect it even wouldn't help if you provided an extra yes response in your Expect prompt logic.
However, there are even other ways how you can connect if you don't care for strict host key checking at all (which maybe isn't advisable in a potentially hostile environment)
You could run the SSH command with the following options:

Code:

$ ssh -q -o BatchMode=yes -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -l remote_login remote_host "command opts args..."

This will (even if the host key changed, or there is a real man-in-the-middle attack!) don't care about the validity of the host key's fingerprint and automatically "add" any offered host key to the bit bucket /dev/null.
The quiet option -q will suppress any warning text of this action,
and BatchMode will not prompt for any passwords or passphrases.
So you should run this command with distributed RSA keys which have either no passphrase attached to them, or have started an ssh-agent a priori which had added the necessary RSA key for this connection.
Please, consult man ssh and man ssh_config for details.

buffoonix

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xrlogin

XRLOGIN(1)						      General Commands Manual							XRLOGIN(1)

NAME

       xrlogin - start an xterm that uses ssh (or optionally rlogin or telnet) to connect to a remote host

SYNOPSIS

       xrlogin [-l username] [-rlogin|-telnet] [xterm options] remote-host

DESCRIPTION

       Xrlogin opens an xterm window and runs ssh, rlogin or telnet to login to a remote host.

       Xrlogin	automatically  passes  the -name argument to xterm with a value of "xterm-hostname" where hostname is the name of the remote host.
       This allows the user to specify resources in their server's resource manager which are specific to xterms from a given host.  For  example,
       this  feature  can  be used to make all xterm windows to a given remote host be the same color or use a specific font or start up in a spe-
       cific place on the screen.  Xrsh(1) passes the same string so they are compatible in this regard.

       Xrlogin specifies that the default title for the new xterm will be "hostname" where hostname is the name of the remote host.  This and  the
       -name argument above can be overridden with xterm-options on the command line.

       One  could  also  use  xrlogin's sister command xrsh(1) to open a window to a remote host.  In the case of xrsh, the xterm would run on the
       remote host and use X as the connection protocol while xrlogin would run the xterm on the local host and use rlogin or telnet as  the  con-
       nection protocol.  See xrsh(1) for a discussion of the merits of each scheme.

OPTIONS

       -l username
	      When not using -telnet, use username as the id to login to the remote host.

       -rlogin
	      Use  the rlogin protocol to open the connection.	In general rlogin is preferred because it can be configured to not prompt the user
	      for a password.  Rlogin also automatically propagates window size change signals (SIGWINCH) to the remote host so that  applications
	      running there will learn of a new window size.

       -telnet
	      Use the -telnet protocol to open the connection. Use of telnet provided mostly for hosts that don't support rlogin.

COMMON PROBLEMS

       Make  sure  that  the  local  host  is  specified in the .rhosts file on the remote host or in the remote hosts /etc/hosts.equiv file.  See
       rlogin(1) for more information.

EXAMPLES

       xrlogin -bg red yoda
	      Start a local red xterm which connects to the remote host yoda using rlogin.

       xrlogin -telnet c70
	      Open a local xterm which connects to the remote host c70 using telnet.

SEE ALSO

       xrsh(1), rlogin(1), telnet(1)

AUTHOR

       James J. Dempsey <jjd@jjd.com> and Stephen Gildea <gildea@intouchsys.com>.

X Version 11							     Release 6								XRLOGIN(1)