Improve uninstallation instructions

Also switches to using `docker system prune -a` for a less invasive
cleanup of Docker images and related resources.

docs/uninstalling.md

@@ -1,24 +1,40 @@
 # Uninstalling
 
-**Note**: If you have some trouble with your installation configuration, you can just [re-run the playbook](installing.md) and it will try to set things up again. You don't need to uninstall and install fresh.
+**Warnings**:
 
-However, if you've installed this on some server where you have other stuff you wish to preserve, and now want get rid of Matrix, it's enough to do these:
+- If your server federates with others, make sure to **leave any federated rooms before nuking your Matrix server's data**. Otherwise, the next time you set up a Matrix server for this domain (regardless of the installation method you use), you'll encounter trouble federating.
 
-- ensure all Matrix services are stopped (`systemctl stop 'matrix*'`)
+- If you have some trouble with your installation, you can just [re-run the playbook](installing.md) and it will try to set things up again. **Uninstalling and then installing anew rarely solves anything**.
 
-- delete the Matrix-related systemd .service files (`rm -f /etc/systemd/system/matrix*`) and reload systemd (`systemctl daemon-reload`)
+
+-----------------
+
+
+## Uninstalling using a script
+
+Installing places a `/usr/local/bin/matrix-remove-all` script on the server.
+
+You can run it to to have it uninstall things for you automatically (see below). **Use with caution!**
+
+
+## Uninstalling manually
+
+If you prefer to uninstall manually, run these commands (most are meant to be executed on the Matrix server itself):
+
+- ensure all Matrix services are stopped: `ansible-playbook -i inventory/hosts setup.yml --tags=stop` (if you can't get Ansible working to run this command, you can run `systemctl stop 'matrix*'` manually on the server)
+
+- delete the Matrix-related systemd `.service` files (`rm -f /etc/systemd/system/matrix*.service`) and reload systemd (`systemctl daemon-reload`)
 
 - delete all Matrix-related cronjobs (`rm -f /etc/cron.d/matrix*`)
 
 - delete some helper scripts (`rm -f /usr/local/bin/matrix*`)
 
-- delete some cached Docker images (or just delete them all: `docker rmi $(docker images -aq)`)
+- delete some cached Docker images (`docker system prune -a`) or just delete them all (`docker rmi $(docker images -aq)`)
 
-- delete the Docker network: `docker network rm matrix`
+- delete the Docker network: `docker network rm matrix` (might have been deleted already if you ran the `docker system prune` command)
 
 - uninstall Docker itself, if necessary
 
 - delete the `/matrix` directory (`rm -rf /matrix`)
 
-The script `/usr/local/bin/matrix-remove-all` performs all these steps (**use with caution!**).
 

roles/matrix-base/templates/usr-local-bin/matrix-remove-all.j2

@@ -24,9 +24,9 @@ else
 	find /etc/cron.d/ -name "matrix-*" -delete
 	echo "Remove matrix scripts"
 	find {{ matrix_local_bin_path }}/ -name "matrix-*" -delete
-	echo "Remove every docker images"
-	docker rmi $(docker images -aq)
-	echo "Remove docker matrix network"
+	echo "Remove unused Docker images and resources"
+	docker system prune -af
+	echo "Remove Docker matrix network (should be gone already, but ..)"
 	docker network rm {{ matrix_docker_network }}
 	echo "Remove {{ matrix_base_data_path }} directory"
 	rm -fr "{{ matrix_base_data_path }}"