How do I define an alternate fallback in ~/.ssh/config?

Question

I have a number of entries in ~/.ssh/config:

Host github.com
  Hostname github.com
  User git
  IdentityFile ~/.ssh/github

Host mydomain.com
  User name
  IdentityFile ~/.ssh/id_rsa

Host [email protected]
  Hostname work.com
  User full.name
  IdentityFile ~/.ssh/work_rsa

If none match, the default fallback is id_rsa. But I'd like a different fallback. The following attempt failed, because it catches everything, overriding any previous settings.

Host '*'
  IdentityFile ~/.ssh/fallback

What is the correct way to express "none of the above"?

Answer 1

Move your fallback to the bottom. SSH takes the parameter value from the first matching Host block.

Since Host * will match everything, you want it last. Otherwise, SSH will always pick its IdentityFile.

Host github.com
  Hostname github.com
  User git
  IdentityFile ~/.ssh/github

Host mydomain.com
  User name
  IdentityFile ~/.ssh/id_rsa

Host [email protected]
  Hostname work.com
  User full.name
  IdentityFile ~/.ssh/work_rsa

Host *
  IdentityFile ~/.ssh/fallback