Today I finally got round to setting up my local user ssh config on my new work laptop and figured I’d do a quick write up on it and it’s uses.
You can create a configuration file in your home directory that will override the options set in your machine-wide config.
Your configuration files
Your local config can be found/created in:
~/.ssh/config
And your machine-wide configuration is in:
/etc/ssh/ssh_config
Rather than editing my ssh config across my whole machine I’m doing it for my local user specifically.
Reading the man page for ssh_config will give you a full list of available options, below I will outline several that I use and find very useful.
Your host definitions
First things first, we need to define a host.
Host host.domain.com
Each host you add to your config will need to have a host definition
Host host.domain.com ... Host host2.domain.com ...
You can also create a wildcard host, hosts will actually build together unless overwritten, so if you set a variable within the wildcard host it will be set on all other defined hosts, unless the option is respecified on that host.
You can set up a wildcard host with this option:
Hostname * ...
Configuration options
I use several options across all my hosts
Compression yes
Setting this to yes will enable SSH compression. See setting below for more information.
CompressionLevel 9
This is used to set compression on SSH, the higher the level (1-9) the higher the compression rate, this also means less bandwidth is needed but will require more processing to actually compress the request. I generally set this in my wildcard host and leave it set.
HostName 192.168.1.2
This is a great little option, it means you can set an IP address to connect to within a host definition, this basically means no more need for /etc/hosts specifically for SSH.
KeepAlive yes
Setting this will enable keep alive packets to be sent to the host, making it easier to continue working after network disconnect.
TCPKeepAlive yes
This option is like the one above, except it only sends TCP keep alive packets.
There are many, many more settings but these are the ones I find useful.
Configuration example
Host host1
HostName 192.168.1.1
Host host2
HostName 192.168.1.2
Host host3
HostName host3.example.com
Host *
Compression yes
CompressionLevel 9
KeepAlive yes
Why use it?
The beauty of this config means that you are able to type ssh, press your Tab key and a whole list of your hosts will be displayed, using the name set in the host definition, just like when you type commands, this also means you could type “ssh h” with the above config file and it will display host1, host2 and host3 for you to chose from.
