What eval and ssh-agent commands do?

I have below commands:

eval $(ssh-agent -s)

'[[ -f /.dockerenv ]] && echo -e "Host *\n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config'

ssh-add <(echo "$PRIVATE_KEY")

Can some one explain what these commands are doing running in ubuntu linux?

1 Answer

Generally speaking, and in the context of a gitlab-runner, they are running in a docker-ized version of Ubuntu to setup the ssh environment (agent, keys, and config) to make it possible for the runner to get access to the git repository.

Specifically:

eval $(ssh-agent -s)

... this starts ssh-agent and configures the environment (via eval) of the running shell to point to that agent. The agent will (below) hold the ssh keys.

'[[ -f /.dockerenv ]] && echo -e "Host *\n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config'

... this (rather destructively) mucks with the ssh config file (~/.ssh/config) to tell ssh not to pay much attention to the host keys that ssh would normally use to ensure your ssh session is connecting only to validated hosts.

ssh-add <(echo "$PRIVATE_KEY")

... and finally, this adds the private ssh key to the agent (started above). The key is then going to be used to allow the runner to gain ssh access to the git remote that holds the code.

If you really want to learn more about how the runner is working, I suggest you use the manual pages to understand each command in sequence.