[systemd-devel] systemd-repart /etc automount via discoverable partition specification

[Nils Kattenbeck]

On Mon, Sep 11, 2023, 10:54 Lennart Poettering <lennart at poettering.net>
wrote:

> On So, 10.09.23 00:33, Nils Kattenbeck (nilskemail at gmail.com) wrote:
>
> > Hello, I am currently trying to build a linux image with discoverable
> > partitions in an A/B+etc+var scheme.
>
> The discoverable partition scheme has no concept of /etc/ discovery. It
> focusses on three basic setups:
>
> 1. writable root fs that contains /etc/, /var/ and /usr/ directly.
> 2. writable root fs that contains /etc/ and /var/ and gets an
>    immutable /usr/ mounted in
> 3. immutable root fs that contains /etc/ and /usr/ directly and gets a
>    writable /var/ mounted in. (the latter possibly as tmpfs, for truly
>    stateless systems)


There is also 4. with a writeable root which only contains /etc, an
immutable /usr and a temporary /var. Though I guess that can be covered
with the existing DPS...?

It was out assumption that these three cases should cover most
> intended behaviours nicely, i.e. systems with modifiable config, code
> and state. systems with modifiable config and state, but immutable
> code. And finally systems with immutable config and code, but
> modifiable state.
>
> A system where /etc/ was separate from the root fs is not covered by
> the above, because it is not clear what that would get us. if you want
> it immutable, why not stick it on an immutable root fs. And if you
> want it writable, why not stick it on a writable root fs directly?


My use case is basically 2, /etc has to be writeable to persist the
machine-id across reboots, /var also has to be writeable and /usr can be
immutable.

The problem I am then likely facing is that I create the partitions wrong.
I am using mkosi and tried several different repart.d configuration with
type=root+type=usr, type=root+type=var+type=use, and different CopyFiles=
and Exclude(Target)Files= but none of them seemed to have worked.

Are there special requirements for what the respective partitions must or
shall not contain when using several auto-discovered partitions? Or should
I ask on the mkosi issue tracker?

Kind regards,
Nils

>
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