CI-CD/System-Details.md

@@ -26,6 +26,16 @@ The following document contains information about the CI/CD system, including so
 |GitLab Runner|14.5.0|`sudo gitlab-runner --version`|
 |Bitcraze Builder Docker Image|(latest)|`docker pull bitcraze/builder:latest`|
 
+# Cleanup
+By default, docker doesn't clean up old images that are used to build the firmware and can easily fill up the storage space on the server. To manage this, a script is run periodically to prune old images. This script is stored at `/etc/cron.daily/docker-prune` and is executed automatically every day by the corn daemon. The script logs all its output to `/var/lib/docker/prune.log`
+
+```bash
+#!/bin/bash
+log=/var/lib/docker/prune.log
+date +'=== %Y.%m.%d %H:%M ===' >> $log
+#remove all dangling docker images that are older than 15 days 
+docker system prune -f --filter "until=$((15*24))h" >> $log
+```
 
 # Software Update Notes