mastercontainer: check if auth.docker.io is reachable during startup

Containers/mastercontainer/start.sh

@@ -283,6 +283,15 @@ if [ "$?" = 6 ]; then
     exit 1
 fi
 
+# Check if auth.docker.io is reachable
+# Solves issues like https://github.com/nextcloud/all-in-one/discussions/5268
+if ! curl https://auth.docker.io/token | grep -q token; then
+    print_red "Could not reach https://auth.docker.io."
+    echo "Most likely is something blocking access to it."
+    echo "You should be able to fix this by using https://github.com/nextcloud/all-in-one/tree/main/manual-install"
+    exit 1
+fi
+
 # Check that no changes have been made to timezone settings since AIO only supports running in Etc/UTC timezone
 if [ -n "$TZ" ]; then
     print_red "The environmental variable TZ has been set which is not supported by AIO since it only supports running in the default Etc/UTC timezone!"

manual-install/readme.md

@@ -6,11 +6,13 @@ You can run the containers that are build for AIO with docker-compose. This come
 - You can run it without a container having access to the docker socket
 - You can modify all values on your own
 - You can run the containers with docker swarm
+- You can run this in environments where access to docker.io is not possible. See [this issue](https://github.com/nextcloud/all-in-one/discussions/5268).
 
 ### Disadvantages
 - You lose the AIO interface
 - You lose update notifications and automatic updates
 - You lose all AIO backup and restore features
+- You lose the built-in [Docker Socket Proxy container](https://github.com/nextcloud/docker-socket-proxy#readme) (needed for [Nextcloud App API](https://github.com/nextcloud/app_api#nextcloud-appapi))
 - You lose all community containers: https://github.com/nextcloud/all-in-one/tree/main/community-containers#community-containers
 - **You need to know what you are doing, especially when modifying the compose.yaml file**
 - For updating, you need to strictly follow the at the bottom described update routine