SSH Without Password

It is possible to ssh from one Linux or Mac machine to another Linux server by using only cryptographic keys instead of using a password.

Create the private key on the source computer

On the source system 192.168.100.1 create the private key with the following command:

cd ~/.ssh
ssh-keygen -t rsa

Choose no passphrase when asked and accept the default filename of id_rsa. This creates both the id_rsa private key file and a id_rsa.pub public key file. Keep the private key on the source system and copy the public key to the destination system.

Move the public key to the destination computer

Now we need the move that public key from the source computer to the destination.

From the source 192.168.100.1 use the following command:

scp id_rsa.pub <user>@<yourhost>:.ssh/authorized_keys

This is the username you normally use to ssh into that system. So if your username was darcy and the destination IP is 192.168.200.1 then the command becomes:

scp id_rsa.pub [email protected]:.ssh/authorized_keys

Testing

Congrats you’ve set up the ssh keys so that you no longer need to use a password when ssh’ing into that system. To test this simply do ssh like normal and it should automatically connect you.

ssh [email protected]

Add an alias

You can add an alias for this command to make it even quicker to get to that system. If you’re using a bash shell simply add this to your .bashrc file on your source computer.

alias s1='ssh [email protected]'

Now you simply need to type s1 and you’ll automatically be logged into that system.

Troubleshooting

Verify you have spelled the .ssh and authorized_keys file correctly.

Sometimes permissions needs to be set on the directory and file. Here are the permissions needed to be set.

chmod 700 .ssh
chmod 600 .ssh/authorized_keys