Setting up SSH in linux

From the command line install open ssh client and server with the following commands:

sudo apt-get install openssh-client sudo apt-get install openssh-server

make a copy of the original configuration file and protect it from being over written with the following commands:

sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.original
sudo chmod a-w /etc/ssh/sshd_config.original

Rather than use a password for logging in we are going to use keys.

mkdir ~/.ssh
chmod 700 ~/.ssh
ssh-keygen -t rsa

note: The default file location is fine. Also be sure to set a good pass phrase. To make sure your key is even more secure we are going to encrypt it at 4096 bits rather than the default 2048:
ssh-keygen -t rsa -b 4096

To transfer the public key from the server (or host computer) to your computer (client) ssh in to the server using the password then issue the following command:

ssh-copy-id <username>@<host>

note: this has to be done using port 22

Next we are going to edit the /etc/ssh/sshd_config

gksu gedit /etc/ssh/sshd_config

note this can also be done with, leafpad, nano. vim, vi....

Since we are using keys instead of passwords we want the following:

PasswordAuthentication no

More security can also be achieved by allowing particular users:

AllowUsers Alice Bob Eve

Now is a good time to set the following:

PermitRootLogin no

AuthorizedKeysFile %h/.ssh/authorized_keys

note: It is also a good idea to change the port from 22 to something else but only after issuing the ssh-copy-id command.

Make sure the following lines are uncommented by deleting the preceding “#” sign.

PubkeyAuthentication yes
RSAAuthentication yes

Personally I also change the following settings:

LogLevel VERBOSE

Banner /etc/issue.net

note: The Banner option lits the contents of /etc/issue.net file when logging in

After saving the file and restart the sshd server by issuing the following command:

sudo /etc/init.d/ssh restart