ssh ABC

Access Remote GUI Programs Using SSH Forwarding
ssh -C -X user@host.domain gnome-terminal

> vi /etc/ssh/sshd_config

and set:
X11Forwarding yes

> vi /etc/ssh/ssh_config

and set:
ForwardAgent yes
ForwardX11 yes
ForwardX11Trusted yes

> /etc/init.d/ssh restart

You done and can connect with forwarding

Auto login via ssh

1. Create a public ssh key, if you haven’t one already.
   ssh-keygen will create key as .ssh/id_rsa
2. Make sure your .ssh dir is 700:
   chmod 700 ~/.ssh
3. Get your public ssh key on the server you want to login automatically.
   A simple scp ~/.ssh/id_rsa.pub remoteuser@remoteserver.com: is ok.
4. Append the contents of your public key to the ~/.ssh/authorized_keys and remove it.
   Important: This must be done on the server you just copied your public key to. Otherwise you wouldn’t have had to copy it on your server.
   Simply issue something like cat id_dsa.pub >> .ssh/authorized_keys while at your home directory.
5. Instead of steps 3 and 4, you can issue something like this:
   cat ~/.ssh/id_rsa.pub | ssh -l remoteuser remoteserver.com 'cat >> ~/.ssh/authorized_keys'
6. Remove your public key from the home directory on the server.

Change ssh port or get more port
sudo vi /etc/ssh/sshd_config

change or add

Port 22
Port 446

Reverse SSH or Tunnel ssh

SSH is one of the most versatile tools for Linux, but most people only ever use it one way - to use the server to send data to the client. What you might not know is that it's also possible to switch the usual logic SSH and use the client to send data to the server. It seems counterintuitive, but this approach can save you having to reconfigure routers and firewalls, and is also handy for accessing your business network from home without VPN.
You'll need the OpenSSH server installed on your work machine, and from there you need to type the following to tunnel the SSH server port to your home machine:

ssh -R 1234:localhost:22 home_machine

You'll need to replace home_machine with the IP address of your home machine. We've used port number 1234 on the home machine for the forwarded SSH session, and this port needs to be both free to use and not blocked by a local firewall. Once you've made the connection from work, you can then type the following at home to access your work machine:

ssh workusername@localhost -p 1234

This will open a session on your work machine, and you will be able to work as if you were at the office. It's not difficult to modify the same procedure to access file servers or even a remote desktop using VNC. The only problem you might find is that the first SSH session may time out. To solve this, open /etc/ssh/sshd.conf on your work machine and make sure it contains 'KeepAlive yes' and 'ServerAliveInterval 60' so that the connection doesn't automatically drop.

this part was adopted from
http://www.tuxradar.com/content/command-line-tricks-smart-geeks