diff --git a/doc/docker/development/README.md b/doc/docker/development/README.md
index acd8aa516d..dff650d9b0 100644
--- a/doc/docker/development/README.md
+++ b/doc/docker/development/README.md
@@ -28,7 +28,9 @@ The container and docker-compose.yml file in this directory are the easiest way
 mkdir dev && cd dev
 wget https://raw.githubusercontent.com/EGroupware/egroupware/master/doc/docker/development/docker-compose.yml
 wget https://raw.githubusercontent.com/EGroupware/egroupware/master/doc/docker/development/nginx.conf
-mkdir sources data
+mkdir -p sources data/default/files/sqlfs data/default/backup sessions
+# on a Linux host NOT using Docker desktop data and sessions directories MUST be owned by www-data:www-data (33:33, if not Debian/Ubuntu!)
+chown -R www-data:www-data data sessions
 # edit docker-compose.yml to fit your needs eg.
 # ports to use for Nginx / the webserver, by default 8080 and 4443
 # xdebug port, default 9001 (NOT 9000!)
@@ -72,7 +74,7 @@ service:
   - prefix them with ```sudo``` or
   - add yourself to the ```docker``` group: ```sudo usermod -aG docker $USER``` and then run ```newgrp docker``` everytime you open a terminal
 * permissions of sources directory need to be changed after install: ```chown -R $USER sources```
-* permissions of data directory must be readable and writable by www-data user (#33)
+* permissions of data and sessions directory must be readable and writable by www-data user (#33): ```chown -R 33:33 data sessions```
 * do not use ```http://localhost/egroupware/```, as push, Collabora and Rocket.Chat will not be able to communicate
   - localhost in each container is NOT the host system, but the container itself!
   - give you development system a name and add it to the hosts ```/etc/hosts``` as: ```127.0.0.1   devbox.egroupware.org```
@@ -82,4 +84,4 @@ Stopping eg. FPM to access IDE/PHPStorm debug port or a MariaDB running on the h
 To fix that, you have to create an explicit firewall rule to allow containers to acces 172.17.0.1:
 ```bash
 sudo ufw allow from 172.16.0.1/12 to 172.17.0.1/32 port 9001,3306
-```
\ No newline at end of file
+```