ssh Command

ssh username@ip-address [-p <port>]
 
# Connect using Key
ssh -i <private-key> username@ip-address
 
# Connect using different shell
ssh username@ip-address -t /bin/sh

INFO

• SSH default port: 22
• SSH with GUI Support: -X (Untrusted Session), -Y (Trusted Session)

Generate SSH Keys

ssh-keygen
# Generate key using specific algorithm
ssh-keygen -t <algorithm>

Copy SSH Keys to Remote Machine

Copy using SSH Copy and SSH Add

# Move key to Remote Machine
ssh-copy-id username@ip-address
 
# Required if above command fails
# No need to specify .pub with this command
ssh-add ~/.ssh/tatu-aws-key
 
# Use if above command does not work
eval `ssh-agent -s`

Copy using Pipes

cat ~/.ssh/<pub-key> | ssh username@ip-address tee ~/.ssh/authorized_keys

INFO

• The public keys of known devices are stored in ~/.ssh/ folder in a file called “authorized_keys”
• SSH Configuration Files: ~/.ssh/ssh_config (Client Config File), ~/.ssh/sshd_config (Server Config File)
• Disable PasswordAuthentication on server if it’s not disabled by default to prevent login with password

Create Alias for Remote Machines

Add the following configuration in ~/.ssh/config

Host <alias_name>
HostName <hostname/ ip-address>
User <username>
IdentityFile ~/.ssh/<my_key>
ForwardAgent yes

IdentifyFile: Used to specify the key to use for the SSH connection
ForwardAgent: Forwards our local SSH Agent to the remote machine. This is useful if we want to use any of the locally saved Host information on remote machine

Connecting to Old Server

Supported Algorithms & Ciphers will be provided by server when we try to establish connection using the normal command

ssh <ip-address> -oKexAlgorithms=+<algorithm-name> -c <cipher-name>