Error resolving hostname on SSH tunnels

Lets say you are trying to create an SSH tunnel.

ssh -L 27017:somehost:27017

You may get the following error message.

ssh: Error resolving hostname \342\200\223L: nodename nor servname provided, or not known

This is caused by using the wrong kind of minus symbol. If you have copied and pasted the command from somewhere, this is probably the case. This is easy to fix – simply paste the command into your terminal, then go through it, remove the existing minus symbol and put a new – in.

Speed up really slow SSH connections

Sometimes, you might find that when you try and SSH into another server, it seems to hang, but then after around 30 seconds or so, will suddenly start working again. You can diagnose where it is stopping by using verbose mode.

ssh -vv user@example-server

If you find it is to do with GSS API, you can disable this in your SSH configuration.

cd ~/.ssh/
vim config

Add the following to it.

GSSAPIAuthentication no

This should then speed the login up.

Changing your SSH port

If you want to change your SSH port to something a little less obvious, it’s easy to do. It’s debatable how much security it actually gives you, but it will certainly make you feel safer, and that is probably the most important thing.

pico /etc/ssh/sshd_config

I’m using pico in this example, but vim will work just as well. You should find a line which is commented out, specifying that the port is 22. This doesn’t need to be uncommented normally, as it defaults to port 22.

#Port 22

Just uncomment this and put a new port number in.

Port 8473

Now save the file and exit. Finally, restart SSH for it to take affect.

/etc/rc.d/init.d/sshd restart

Don’t forget, next time you SSH in you will need to use the new port number!

ssh -p 8473 hostname