$HOME/.ssh/config and host/hostname resolution how-to?

Darren Tucker dtucker at zip.com.au
Thu Dec 20 07:40:01 EST 2007

Duncan Ferguson wrote:
> Hiya,
> What is the easiest way of looking up a hostname to see if it exists,  
> taking into account the .ssh/config file?
> If i have an entry in my file
> host host1
>    hostname server.domain.name
> then usual OS calls won't recognise the 'alias' host1.  So, i need to  
> make a call via ssh somehow to check if the name resolves without  
> actually initiating a full blown 'expensive' connection to it, such  
> as using 'ssh host1 true' or something (which also relies on 'true'  
> being on the path, or always being installed in the same place if the  
> path is provided - neither of which can be guaranteed).
> I tried ssh-keyscan, but this ignores the config file (probably  
> correctly), so what is the more appropriate way to perform the name  
> validation?  I have tried 'ssh -n host1' which seems to work - would  
> this be the best option?

I'm not quite sure what you're trying to achieve, could you give an example?

Depending on what you want, there's a couple of options.

If you just want to return quickly if the host is down, you can set the 
ConnectTimeout to a lowish value.

If you want to do something more complicated, (eg fail if your 
dial-on-demand link is down or similar) you could use a ProxyCommand and 
implement whatever logic you want in a shell script (that finishes by 
exec'ing netcat).

Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
     Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.

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