SSH agent for password-less login

2021-01-17

I have numerous machines I frequently log in to and from via SSH. Typing in a password every time is tiresome and a password-less key is not an option. A solution is an SSH agent running in the background, which prompts for a password once at log in, and stores it for the duration of the session (until reboot). The following can live in your shell's startup file (e.g. ~/.zshrc).

if [ ! -S $HOME/.ssh/ssh_auth_sock ]; then
  eval "$(ssh-agent)"
  ln -sf "$SSH_AUTH_SOCK" $HOME/.ssh/ssh_auth_sock
fi

export SSH_AUTH_SOCK=$HOME/.ssh/ssh_auth_sock
ssh-add -l > /dev/null || ssh-add

Then, just copy the needed key between machines with ssh-copy-id -i ~/.ssh/id_xxx.pub name@host.

MacOS however, has its own provision for this. The following can simply be added to your ~/.ssh/config file:

Host *
  UseKeychain yes
  AddKeysToAgent yes
  IdentityFile ~/.ssh/id_ed25519