Add `NEXTCLOUD_INIT_LOCK` to enable shared html volume update

Signed-off-by: John Molakvoæ <skjnldsv@protonmail.com>

README.md

@@ -137,6 +137,10 @@ The install and update script is only triggered when a default command is used (
 
 - `NEXTCLOUD_UPDATE` (default: `0`)
 
+If you share your html folder with multiple docker containers, you might want to avoid multiple processes updating the same shared volume
+
+- `NEXTCLOUD_INIT_LOCK` (not set by default) Set it to true to enable initialization locking. Other containers will wait for the current process to finish updating the html volume to continue.
+
 If you want to use Redis you have to create a separate [Redis](https://hub.docker.com/_/redis/) container in your setup / in your docker-compose file. To inform Nextcloud about the Redis container, pass in the following parameters:
 
 - `REDIS_HOST` (not set by default) Name of Redis container

docker-entrypoint.sh

@@ -103,12 +103,13 @@ if expr "$1" : "apache" 1>/dev/null || [ "$1" = "php-fpm" ] || [ "${NEXTCLOUD_UP
         fi
 
         # If another process is syncing the html folder, wait for
-        # it to be done, then escape initalization
+        # it to be done, then escape initalization.
+        # You need to define the NEXTCLOUD_INIT_LOCK environment variable
         lock=/var/www/html/nextcloud-init-sync.lock
         count=0
         limit=10
 
-        if [ -f "$lock" ]; then
+        if [ -f "$lock" ] && [ -n "${NEXTCLOUD_INIT_LOCK+x}" ]; then
             until [ ! -f "$lock" ] || [ "$count" -gt "$limit" ]
             do
                 count=$((count+1))