[Linux](EN) Disable host key checking while connecting ssh

Summarize methods to disable host key checking while connecting ssh.

Environment and Prerequisite

• Linux
• SSH(OpenSSH)

Host Key Checking

• When we connect to remote server by using ssh, client compares client’s saved key and remote server’s key to authenticate server.
• This process prevents from Man-in-the-middle attack.

Disable Host Key Checking When Using SSH

• Remote host’s key will be added if there is no added key in ~/.ssh/known_hosts.
• Connect to remote server even though saved key is different from server’s key.

1. Disable when using ssh command

• Use StrictHostKeyChecking=no option.

ssh -o StrictHostKeyChecking=no [DOMAIN_OR_IP]

2. Edit ssh config file

~/.ssh/config

• Add option to specific host like below.

Host twpower-private-server
    HostName [IP ADDRESS]
    StrictHostKeyChecking no
    Port 22
    User [USERNAME]
    IdentityFile [IDENTITY KEY FILE]

/etc/ssh/ssh_config

• There is * in config file. So this disables host key checking to all hosts.
• /etc/ssh/ssh_config defines all the default settings for the client utilities for all users on that system.

Host *
    StrictHostKeyChecking no

Reference

• https://askubuntu.com/questions/87449/how-to-disable-strict-host-key-checking-in-ssh
• https://en.wikibooks.org/wiki/OpenSSH/Client_Configuration_Files#~/.ssh/known_hosts