I often do a lot of work with temporary Vagrant, Docker, VMs, and I don’t really want those host keys clogging up my ~/.ssh/known_hosts file. So I just add the following alias to my shell “rc” file. In my case, I use zsh so it’s ~/.zshrc :

alias ssh-nocheck="ssh -o 'StrictHostKeyChecking no' -o 'UserKnownHostsFile /dev/null'"

Viola!  Now all I need to is to use something akin to:

ssh-nocheck -p 2222 root@192.168.2.138