I’m Patrick. I’m a data scientist with an IT background who loves working on the whole stack, walking places and finding interesting things to eat off the beaten path. Before coming to New York City I lived, worked and studied in Los Angeles and Boston.

1 minute read

I do my work on a few different machines at once, and in order to keep things reasonably sane I like to sync my client machines back to my share hosted on the department server. I do this with some simple rsync scripts, and to facilitate the connection I use shared SSH keys. For one reason or another I find myself recreating these a few times a year, and so to find the instructions I post them here. (Thanks to [Debian Administration] (http://www.debian-administration.org/articles/530) from whom I draw the info.)

I write this to connect my Debian/Ubuntu VMs to OS X Server, I suspect it will work for any *NIX-to-*NIX link.

On the local machine, generate keys

mccarthy@StatsVM:~$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/mccarthy/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/mccarthy/.ssh/id_rsa.
Your public key has been saved in /home/mccarthy/.ssh/id_rsa.pub.
The key fingerprint is:
11:a3:4d:11:22:56:c8:07:41:2c:91:13:b6:e5:10:ce mccarthy@StatsVM
The key's randomart image is:
+--[ RSA 2048]----+
|  *OB=o *o       |
| ++*+..= o       |
|  Eo... o        |
|         .       |
|        S        |
|                 |
|                 |
|                 |
|                 |
+-----------------+

There’s a tradeoff here– for an automatic connection the passphrase should be set to blank (‘enter’ when prompted), however if someone obtains the key they then can connect as you do. A passphrase that only you know obviates the problem, but then the connection can’t be unattended.

SSH typically comes with a utility called ssh-copy-id which adds the contents of the id_rsa.pub file you just generated to ~/.ssh/authorized_keys on the server.

mccarthy@StatsVM:~$ ssh-copy-id -i .ssh/id_rsa.pub pmccarthy@myfiles.stat.ucla.edu
The authenticity of host 'myfiles.stat.ucla.edu (128.97.55.245)' can't be established.
RSA key fingerprint is 36:69:9c:59:d5:16:a1:b0:da:21:2d:b1:50:34:4e:ed.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'myfiles.stat.ucla.edu,128.97.55.245' (RSA) to the list of known hosts.
Password:
Now try logging into the machine, with "ssh 'pmccarthy@myfiles.stat.ucla.edu'", and check in:

  ~/.ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

And so we test as it says:

mccarthy@StatsVM:~$ ssh pmccarthy@myfiles.stat.ucla.edu
Last login: Wed Sep 26 22:48:18 2012 from 76.89.183.15
[myfiles:~] pmccarthy%

Success!

This will pave the way for my file-syncing script.

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