Enabling Read Only File System changes all connected filesystems to read only

[wrt54gl]

I have been using raspberry pi's with the Overlay read-only file system for some time and have been very happy with it.
In my standard builds I have created another partition on the sd card for any data that I need RW access to then I have just used raspi-config to enable the Overlay File System.
This has worked well up until Bookworm. In Bookworm, when the read-only file system is enabled it changes all the mounted partitions to read only (except /boot).
Is there a way to exclude certain partitions or limit it to only the root partition? I cannot seem to find a way to do this.

[wrt54gl]

Forgot to mention. This using Raspberry pi OS lite 64 bit.

[wrt54gl]

After much hacking and googling on this:
raspi-config adds overlayroot=tmpfs in cmdline.txt to switch the overlayfs on.
If you change that to overlayroot=tmpfs:recurse=0 then the overlay file system will behave like before.
You can see all the options in /etc/overlayroot.conf
I would suggest a change to raspi-config to use this as its default behavior.

[ghollingworth]

Had a chat with Serge about this, since we're now using the standard overlayroot package to do this, we prefer to go with their default options (they've probably thought about the options more than we have!)

You can find more information in /etc/overlayroot.conf of other options available. We could add an option in raspi-config to select the different behaviour, but it feels difficult to explain the behaviour for most of our users here. Of course, maybe this all belongs in an "industrial" whitepaper somewhere instead...

[lurch]

ping @aallan in case he wants to mention this in the documentation.

[aallan]

Yeah, we should probably mention this in the documentation somewhere. I'll spawn an issue.

[JinShil]

I think there is still a problem here. According to the documentation, you should be able to configure the overlay by editing /etc/overlayroot.conf, or better, /etc/overlayroot.local.conf. So, I think rapi-config should do the following:

1. Create /etc/overlayroot.local.conf with the line overlayroot="tmpfs" if it doesn't exist.
2. If the file does exist, prepend tmpfs to the overlayroot value.

I don't think raspi-config should modify /boot/cmdline.txt at all.

I tested this myself and it seems to work.

[JinShil]

Ah, but how does one disable the overlay if one can't write to /etc/overlayroot.local.conf after the overlay is enabled?

Then explicitly adding overlayroot="" to /boot/cmdline.txt seems to work, but I hope there is a better way.

[XECDesign]

I don't think raspi-config should modify /boot/cmdline.txt at all.

Why not?

[wrt54gl]

Confusing behavior to say the least. It seems that it needs both /etc/overlayroot.conf and cmdline.txt settings to work currently.
I thought I had everything set up and then it quit working. I completely re-installed but could not get it to work until I set both places... I would support not using cmdline.txt because there is not much documentation online for that.

[XECDesign]

Hmm, in my testing, I didn't come across any cases where things didn't "just work" as advertised.

If you can give a set of instructions that get overlayroot to work in a way that doesn't match what's documented in the conf file comments, I can take a closer look.

[wrt54gl]

I ran out of time on this project. Seems to need the setting in both places if overlayroot=tmpfs:recurse=0 is used. Maybe someone else can verify. Otherwise it will be a while before I can verify it.

[XECDesign]

Okay, just did some more testing and having it in either cmdline.txt or overlayroot.conf works.

cmdline.txt overrides whatever you set in the conf file.

So, you could have overlayroot=tmpfs:recurse=0 in the conffile and remove the parameter from cmdline.txt altogether.

Then if you want to disable it, you can add overlayroot=disabled in cmdline.txt.

[wrt54gl]

Okay, just did some more testing and having it in either cmdline.txt or overlayroot.conf works.

cmdline.txt overrides whatever you set in the conf file.

So, you could have overlayroot=tmpfs:recurse=0 in the conffile and remove the parameter from cmdline.txt altogether.

Then if you want to disable it, you can add overlayroot=disabled in cmdline.txt.

Makes sense. Thanks for looking into that.