Saving Storage Space
How to free up disk space on your Garry's Mod server by clearing cached workshop content.
If your service is running low on disk space, the most common cause is cached Workshop content building up over time. Addons downloaded from a collection are cached so they don't need to be re-downloaded on every restart, but old/unused addons aren't cleaned up automatically.
Safe to delete
Both folders below are just a cache. Deleting them doesn't remove your actual addon files or configuration, your active Workshop content will simply be re-downloaded the next time your server starts.
Stop your server
Navigate to the game panel, select your service, and stop it before continuing.
Delete the steam_cache folder
Using SFTP or the file manager, delete the steam_cache folder in the root of your service.
Delete the garrysmod/cache folder
If present, also delete the garrysmod/cache folder.
Start your server
Start your server back up. Your active Workshop addons will automatically re-download, only what's currently used by your collection/gamemode will come back, freeing up space taken by anything no longer in use.
Common Issues
"Error! Failed to read the downloaded file"
This is usually caused by a corrupted cache entry. Delete appworkshop_4000.acf from the steam_cache folder (or delete the whole steam_cache folder as above) and restart your server.