Excluding directories from backup
Many applications generate large amounts of temporary or recoverable cache data (e.g. node_modules
, thumbnail caches). This data usually does not need to be included in backups. The Cache Directory Tagging Specification standard exists to tag directories that contain such data. It defines a small tag file called CACHEDIR.TAG
, which is stored at the root of a cache tree. These directories will then no longer be included in our backups.
For the automatically installed apps in mStudio, we have already placed the file in useful locations.
TL;DR
Create a file CACHEDIR.TAG
in each cache directory with exactly the following first line:
Signature: 8a477f597d28d172789f06886806bc55
Requirements
There are only a few requirements for a valid CACHEDIR.TAG
file:
- Filename: Must be exactly
CACHEDIR.TAG
(capitalisation important) - Signature header: The first line must read exactly:
Signature: 8a477f597d28d172789f06886806bc55
- Placement: A single
CACHEDIR.TAG
in the top-level cache directory is sufficient to mark the entire underlying directory tree as cache
When should you tag a cache directory?
Use CACHEDIR.TAG
for directories whose content is regenerable - i.e. data that can be loaded from other sources or regenerated at any time. Typical examples:
- Package/build caches (Composer, npm, Yarn)
- Application caches (like TYPO3's
var/cache
directory) - Generated artefacts (thumbnails)
- Backup directories managed by the application (e.g. Updraft)