25.2.1.2 User Configuration Files in ~/.ssh on the Server

On the server side, the ~/.ssh directory usually contains the following files:

authorized_keys: Contains your authorized public keys. The server uses the signed public key in this file to authenticate a client.
config: Contains client configuration settings. This file is optional.
Caution
A config file can be readable and writable by the user but must not be accessible to other users.
environment: Contains definitions of environment variables. This file is optional.
rc: Contains commands that ssh executes when a user logs in, before the user’s shell or command runs. This file is optional.

For more information, see the ssh(1) and ssh_config(5) manual pages.