Matomo upgrade 5.6.2 → 5.7.0 — Unable to write in the cache directory

Recently, I upgraded Matomo from 5.6.2 to 5.7.0. Right after the upgrade, I encountered an error — especially when trying to add users.

The issue

Error: Unable to write in the cache directory (/var/www/html/tmp/templates_c/16).

After logging out, the same error also appeared when attempting to log back into the instance.

Environment

• Matomo: 5.7.0 (upgraded from 5.6.2)
• Deployment: Docker container
• Stack: Apache / PHP (Docker image)
• JElastic Cloud (PaaS) on Infomaniak

Analysis

After a quick search, I found this Matomo forum thread: https://forum.matomo.org/t/unable-to-write-in-the-cache-directory-after-update-to-2-16-0/17979

This type of error is typically related to Matomo’s template cache.

Solution: clear the cache

Once inside the container, I ran:

rm -rf /var/www/html/tmp/templates_c/*

After clearing the cache, I could log in again without errors 😁.

A good reminder that after a version upgrade, the cache often deserves a quick cleanup.