[Techtalk] Incorporating ssh into a bash script

[Conor Daly]

On Sat, Jan 25, 2003 at 08:39:52PM +0100 or so it is rumoured hereabouts, 
Hamster thought:
> Daly,
> 
> > Now that my back-up server is working fine, my boss
> > wants me to create a bash script that will ssh into
> > our remote database server, create a tar ball of the
> > database and copy the tar ball to the backup server. 

Can I suggest rsync here?  rsync works much like the cp command except
that it copies only what's changed.  If you have a 2Gb database of which
20Mb changes each day, using tar -> cp will transfer the same 1.99Gb every
night while rsync will transfer only the 20Mb of changes.

> ssh can be invoked in the following manner:
> 
> ssh -l root 192.168.100.1 tar - /some/directory >some.file
> 
> ie, you can append the command to be run on the remote machine to the end of
> the ssh line.
> 
> But in order for this to work in a shell script, you will have to set it up so
> that the remote machine doesnt ask you to login. This is achieved by setting up
> ssh to use pass-phrase-less keys for authentication. 
> 
> This means that instead of a username and password, the authentication is done
> by the exchange of keys.
> 
> Once this is setup, you can have a shell script that includes something like
> the following (note this isnt the only way of doing it)
> 
> ssh -l root 192.168.1.1 tar -c /some/dir > /root/name.of.tar
> scp root at 192.168.1.1:/root/name.of.tar /home/root


There was a brief thread here last June on "rsync with ssh using cron".
Essentially what you're going to do. In particular, there's a link to a
document by Rick Moen detailing the passphraseless rsync over ssh method.
It includes the detail of how to lock down the passphraseless key to only
this task[0] and to only your host.  It's out there at:

http://linuxmafia.com/~rick/linux-info/ssh-publickey-process

As for the cron bit, it's simply a matter of:

crontab -e

add a line of the form

35 18 * * * /home/daly/rsync_database.sh

and save.  That will run the script "/home/daly/rsync_database.sh" every
day at 18:35

Conor (who uses "Daly" at the _other_ end...)

[0] useful for when your private key somehow gets stolen 'cos the database
server will only run its side of the rsync transaction in response to that
key.  
-- 
Conor Daly <conor.daly at oceanfree.net>

Domestic Sysadmin :-)
---------------------
Faenor.cod.ie
 12:20am  up 81 days,  9:04,  2 users,  load average: 0.08, 0.02, 0.01
Hobbiton.cod.ie
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