Three helpful SSH tips for developers

If you're a developer that deploys stuff to unix systems, then one of the most common tools you interact with is SSH. It never ceases to amaze me, in spite of this, how little developers really know about SSH.

SSH config file

The first thing any developer needs to know is that SSH has a config file that allows you to configure defaults for SSH on a host by host basis. It also allows aliases, and bash completion can use this config file to make sshing into a system much easier. This file lives under the .ssh folder in your home directory, ~/.ssh/config. Here's a sample of things that I have in my config file.

Host home

    HostName jamesroper.homelinux.org

    Port 2222

    User james

Host sshjump

    Hostname sshjump.atlassian.com

    User jamesroper

    ForwardAgent yes

So I can SSH home by running ssh home and that will automatically use james as the username, jamesroper.homelinux.org as the host name, and 2222 as the port number. For details on all the configuration just read the man page, man ssh_config. You'll see that you can configure everything including port forwarding and much more.

Jump boxes

There are a number of times when I need to SSH into a jump box to SSH to another system. The annoying thing about this is to get to a system, I need to run two commands, and scp is even more annoying because I have to copy first to the jump box, then to the remote system.

Enter ProxyCommand. The proxy command config option allows you to specify a command that SSH will run first in order to establish the connection to the remote system, and then it will pipe its communication through that command. Combined with nc on the jump box end to create a TCP connection to the your destination host, this can be used to tunnel an SSH connection through another SSH connection. The configuration in the SSH config file looks like this:

Host *.atlassian.com

    ProxyCommand nohup ssh sshjump nc -w1 %h %p

The other thing I've made use of here is wildcards, and the ability for SSH to substitute the host name and port number for the particular host into option values. Now I can run ssh jira.atlassian.com, and the SSH connection will be piped through an ssh connection to sshjump, which is an alias defined above as sshjump.atlassian.com. I can also scp directly.

Read more: Atlassian blog

Posted via email from Jasper-net