What immutable means
Not "discouraged from changing" — structurally unable to change. Here is exactly which parts of the disk are read-only and which are yours.
The system image
Immos boots from a read-only filesystem image. Not a normal filesystem mounted read-only, which you could remount — the image is stored in a format that has no concept of writing at all. There is no flag to flip and no command to run.
Everything under /usr — every program, library, kernel module and vendor default that makes up
the operating system — lives in that image and is identical on every machine running the same
version.
What is writable
Exactly three things:
| Path | What it holds | Survives updates? |
|---|---|---|
/home |
Your files, settings and application data | Yes |
/var |
Installed Flatpaks, logs, system data | Yes |
/etc |
System configuration you have changed | Yes |
/etc is the interesting one. It is a layered filesystem: underneath sits the pristine
configuration from the image, and on top sits a writable layer holding only the files you have
actually modified. Edit /etc/fstab and your version is stored in the upper layer; every file
you have not touched keeps tracking the vendor default and gets updated with each release.
What you cannot do
- Install system packages. There is no package manager and no compiler in the running system. Software comes from Flathub or a container.
- Modify system files.
/usris genuinely read-only. Scripts that expect to write there will fail, immediately and clearly. - Break the system by accident. A misconfigured
/etcfile is still possible, and is still recoverable — see snapshots and rollback.
What you get in exchange
Because the system cannot drift, an Immos machine on version 0.2.0 is the same machine as every other Immos machine on 0.2.0. Updates are a swap of one known image for another known image, and undoing one is a swap back. There is no accumulated local state for a change to interact badly with.
Your files are separate
Rolling back only changes the system image. Your home folder, documents and application data are never touched.Where the image comes from
Immos is built from Gentoo. The build machine compiles the entire system from source with a fixed configuration and produces the image as an artifact — then the toolchain is stripped out, so the shipped system contains no compiler, no package database and no build tools. Gentoo is the factory; it does not come with the car.