CIS241

System-Level Programming and Utilities

Advanced SSH - Keys and Hostnames

Erik Fredericks, frederer@gvsu.edu
Fall 2025

Based on material provided by Erin Carrier, Austin Ferguson, and Katherine Bowers

ssh is fine - but...

• Lots of typing!
• You have to remember eos##.cis.gvsu.edu
  • Or worse, an IP address
• Also you can't see your password
  • False it is hunter2 but I just see *******

Let's create a hostname alias!

In your ~/.ssh/ directory:

• Create (or edit) a file named config

In that file, add:

Host eos01
Hostname eos01.cis.gvsu.edu
User yourusername

And then: ssh eos01

Now, ssh keys!

We can skip the whole password thing and use encrypted keys!

Default locations (on the machine you're ssh'ing from)

• ~/.ssh/id_rsa - private key
• ~/.ssh/id_rsa.pub - public key

Using ssh keys

1. First, make sure you don't have them already

• ls -la ~./ssh

2. Generate the keys

• ssh-keygen

3. Share the public key (add to ~/.ssh/authorized_keys)

• ssh-copy-id -i path_to_key username@server

Common issues

• Errors with authorized_keys file

  • Make sure the file exists: touch ~/.ssh/authorized_keys

• Wrong permissions

  • chmod 600 ~/.ssh/authorized_keys
  • chmod 700 ~/.ssh

• If you have ssh and ssh-keygen but not ssh-copy-id

  • We can manually copy the key and add it to the file
    • scp ~/.ssh/id_rsa.pub username@hostname:~
  • Login to server via ssh
    • cat id_rsa.pub >> ~/.ssh/authorized_keys