SSH - why can I never remember this stuff?

A short post containing all the useful ssh stuff I forget on a regular basis.

Last updated: 2019-06-06.

Where are my SSH keys anyway?

Unless you need to generate yourself some new ones they'll be in ~/.ssh If you need to make some run: ssh-keygen and follow the instructions - need more detail? Digital Ocean's How to Configure SSH Based Authentication on a Linux Server walks you through the whole process.

Where do I put my public key?

It needs to end up in ~/.ssh/authorized_keys on the computer you're aiming to log in to. The simplest way to do this (if you can) is to use ssh-copy-id [email protected] which scans your local account for your id_rsa.pub file and copies it across to your end point. If you can't do it that way then you'll need to cat ~/.ssh/id_rsa.pub and paste the result either directly into your authorized_keys file or into the appropriate GUI box in the service you're trying to access (GitHub for example). If you cant use ssh-copy-id but do have password based SSH access you can use the following command to cat the file directly onto your server: cat ~/.ssh/id_rsa.pub | ssh [email protected] "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"

What is .ssh/config?

For more complex commands (or just ones you type regularly) it's simpler just to put the relevant information into a config file (~/.ssh/config). The basic structure for each entry should be:

Host shortname
    HostName url_of_server
    User username
    IdentityFile ~/.ssh/ssh_key

You're not necessarily going to need all of these all of the time, for example you only need to specify the identity file if you're not using id_rsa and you can set the Host value to the hostname unless like me you're super lazy and want to be able to type a very small number of characters in order to perform the whole command.

OK, so how do I use my ssh key with rsync / scp?

rsync should just work™.

scp on the other hand defaults to password so you need to add the following -i ~/.ssh/id_rsa after scp in order to make it use the rsa key.