Cache directory permission errors after app installation

Cache directory permission errors after app installation

When installing applications on Yunohost v4.x, the system creates per-app cache directories under /var/cache/yunohost/ with ownership and permission settings that must align with the application's runtime requirements. The documented behavior shows that cache invalidation occurs during package updates, but certain applications may skip proper cache headers, potentially leaving stale data accessible.

System logs indicate 'Cache directory not writable' errors when nginx worker processes lack proper permissions to access the cache directory. This suggests a potential misalignment between the cache directory permissions set during installation and the runtime requirements of specific applications.

The Yunohost web admin interface displays 'Cache Error' when php-fpm fails to clear opcache after app upgrades, indicating that cache-related issues can manifest in multiple ways across different system components.

Which permission model should be applied to ensure cache directories remain accessible to both nginx worker processes and php-fpm during application lifecycle operations, and how can this be verified across different application types?