To configure an SSH server to provide shell access, follow these steps:
1. Install an SSH server on your machine. On Linux, this can usually be done with the following command:
```
sudo apt-get install openssh-server
```
1. Open the SSH configuration file, usually located at `/etc/ssh/sshd_config`.
1. Uncomment the `Port` line and specify the port number you want to use for SSH connections.
1. Uncomment the `PermitRootLogin` line and set it to `no` (unless you want to allow root login).
1. Uncomment the `PubkeyAuthentication` line and set it to `yes`. This enables public key authentication, which is more secure than password authentication.
1. Add any additional configuration options you want, such as `AllowUsers username` to restrict access to specific users.
1. Save the configuration file and restart the SSH server with the following command:
```
sudo service ssh restart
```
Once the SSH server is configured, you should be able to log in to it with an SSH client, such as the `ssh` command on Linux or PuTTY on Windows, using a valid username and password or public key. You will be presented with a shell prompt, allowing you to execute commands on the remote machine.
