Secure Shell (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. At the School of Computer Science, we use ssh for remote connection logins to our computers.

Logging in to Linux using ssh
ssh-key logins
key-exchange errors
host identification error
No matching key exchange method found ERROR

Logging in to Linux using SSH

There are two ways to login to a remote Linux server using SSH:

  1. terminal server (text only)
  2. remote desktop (graphical/X11)
    Not all servers support X11-sessions. Check the servers’ capabilities for remote desktop connections.

IMPORTANT: Carleton is behind a firewall. If you are outside of Carleton, you will need to VPN to Carleton first before you can access the SCS server resources. Refer to the Remote Access (VPN) information.

Login using ssh to Linux using the terminal

If your computer is running Windows, you can use the free putty utility as your ssh client.

Login using ssh to Linux using the graphical method

At SCS, we use the x2go client to connect to a Linux host graphically (using X11).

ssh-key logins

We encourage the use of ssh-key logins as it is both a convenient and safe way to ssh to your destination host without needing a password.
See the Passwordless SSH With Key Pairs article for detailed instructions.

Key Exchange Errors

Annually the omicron servers are upgraded, and the ssh-keys will no longer match. If you know that the server has been upgraded and your ssh-keys no longer match, then it will be safe to accept the new ssh key. Your system administrator will be able to confirm if this is due to a legitimate server upgrade or if it is a ‘man in the middle attack’.

Linux: Host Identification has changed ERROR

In Linux, when a host has changed, it can generate the ‘host identification error’ and the entry can be updated as follows:
ssh-keygen -R <user>@<hostname>
Where <user> is your username and <hostname> is your destination hostname.

No matching key exchange method found ERROR

Some ssh clients may complain about: “Unable to negotiate with port 22: no matching key exchange method found.” 

This is due to the destination server running an old ssh-cypher. Be aware that this may be an insecure connection as the cypher itself is no longer secure. You can try connecting as follows:

ssh -oKexAlgorithms=+diffie-hellman-group1-sha1

You may want to contact the system administrator to inform them of the outdated ssh-server.