I'm running Linux Mint Debian Edition on a roughly 2017 Lenovo Chromebook that has become my main computer. It has only 4GB of soldered RAM and a 32GB soldered eMMC drive, so I'm trying to avoid wearing out the storage or running out of space. I usually keep applications on the eMMC and personal data on microSD cards.
I recently removed my Flatpak installations and replaced the applications with AppImages that I could store on the microSD card. The change freed about 9GB on the eMMC, while the AppImages themselves use only around 1.3GB on the card. I expected AppImages to be larger because each one has to bundle its own dependencies instead of sharing them.
Why might the Flatpaks have taken so much more space? What are the practical downsides of AppImages, and what problems does Flatpak solve that I might be overlooking? Also, is there a reliable way to tell whether this machine is actually using swap frequently?
3 Answers
The main AppImage downside is convenience and integration. Updates are generally your responsibility, desktop menus and file associations may need extra setup, and sandboxing is not automatically provided. A poorly built AppImage can also bundle outdated libraries or have permission and hardware-access quirks.
AppImages run from a mounted filesystem image, commonly through FUSE. Startup or heavy read activity can be measurably slower, though it often isn't noticeable on a lightly used application. Flatpak provides a more standardized installation and update system, shared runtimes, desktop integration, and permission sandboxing. Which format is preferable depends on the specific application and how much you value those features.
Flatpaks include runtimes: collections of shared libraries that applications can use. Those runtimes are shared only when applications use compatible versions, and each runtime may contain many libraries that a particular application never needs. You may also have had several unused runtimes or desktop-integration packages left behind.
An AppImage is usually built around the individual application and the libraries it actually needs, plus a small amount of packaging overhead. That can make it smaller in this particular comparison, although AppImages are not inherently smaller than Flatpaks. Different application versions, leftover Flatpak data, and whether the AppImage is really a full bundle can all affect the result.
Don't assume that swap is being used heavily just because the computer has 4GB of RAM. Check it directly with `free -h`, `swapon --show`, or your system monitor. Some swap usage can remain after memory pressure has passed and does not necessarily mean the machine is constantly swapping.
Keeping free space is sensible, but modern flash storage uses wear leveling, so simply filling particular visible directories doesn't mean writes are restricted to those exact cells. Heavy swap activity can increase writes, though, and running applications from the microSD card may be slower and the card may be less durable than the internal eMMC. The biggest practical win here is probably freeing space and avoiding unnecessary writes, not switching formats as a guaranteed way to extend the drive's life.
That explains the surprise. I had removed the unused packages first, but there still seemed to be several gigabytes of desktop-related runtime files that the handful of applications didn't really need.