Disconnect from an SSH session

~.

Disconnect from a nested SSH session

Disconnect from an ssh session 2 levels deep.

~~.

X11 forwarding not working

Run ssh in verbose mode and make sure xauth is working.

debug1: Requesting X11 forwarding with authentication spoofing.
debug2: channel 0: request x11-req confirm 1
...
debug1: Remote: No xauth program; cannot forward X11.
X11 forwarding request failed on channel 0

Install xauth and it might work. For openSUSE I had to mkdir -p /usr/X11R6/bin && ln -s /usr/bin/xauth /usr/X11R6/bin/xauth to make it work.

get a fingerprint from a public key in your known_hosts file

Stupid trick time:

grep github ~/.ssh/known_hosts | ssh-keygen -l -f -

This will print out the fingerprints for each entry that matches the grep.