cheat sheets.

Authenticating via key pair (password-less)

connecting from client to server (all command lines are run from the client)

 create the key pair (ALWAYS give a strong password)
  $ ssh-keygen

 authorize client's key with server
  $ cat ~/.ssh/id_rsa.pub | ssh user@server \
        'mkdir ~/.ssh; touch ~/.ssh/authorized_keys;
         chmod a=,u=Xrw -R ~/.ssh;
         cat - >> ~/.ssh/authorized_keys'

After that, you should be able to login to server using the password that you
used to encrypt your private key.  If you password protected your private key
(strongly recommended), then you should run ssh-agent within your session, and
then add the key to the agent:

 see if ssh-agent is running (some systems start it up by default)
  $ ps `echo $SSH_AGENT_PID`

 if ssh-agent isn't running
  $ eval `ssh-agent`
 or find a way to run it when your login session starts

 add your key to the agent
  $ ssh-add

After that, you should not need to type the password again during this session.

See http://uwstopia.nl/blog/2006/08/password-hell-gdm-ssh-gnome-keyring to make
ssh-add unnecessary.

SSH Tunnel

$ ssh -f -N -L localport:destination:destport user@remotehost