June 2025 development update

[parke]

Someone asked me via email for an update on the development of Lxroot. Specifically, the differences between the released version (0.22.1) and the unpublished changes I have been working on.

I am at present working on getting all the unpublished changes into a releasable state. I hope this release happens by the end of August, 2025. (It may happen sooner.)

The major unpublished changes are:

• Lxroot worlds.
• Seccomp interception of calls to chown.
• Various usages of tmpfs filesystems. (But I may be unhappy with the current implementation.)

Lxroot world are currently described in the main Readme. I find worlds to be very convenient when I want to share one or more directories across multiple different chroot environments. (More details here.)

The Seccomp chown filters are useful for making calls to chown appear to succeed. This may assist with running Arch's pacman package manager inside of Lxroot. However, there are also other workarounds for pacman that do not require the use of seccomp filters. (But the seccomp filters may be more convenient.)

The tmpfs improvements perform special binding of /tmp, /var/tmp, /run, and /dev/shm. By default, those directories will (may?) all be bound to an ephemeral tmpfs filesystem. However, this behavior might be undesirable, confusing, and surprising. So I may revisit these design decisions prior to publishing the update. I expect that I will keep some form of special processing of those four directories. But I may somehow make the special processing opt-in, rather than on-by-default.

At one point, I added OverlayFS support to Lxroot. But I found it confusing to use, ended up not using it (I prefer using worlds), and may have removed the OverlayFS code.

There is also a bunch of general maintenance improvements in the unpublished version of Lxroot. These changes probably won't affect end users, but reduce the labor required to maintain and extend Lxroot.

Please feel free to ask any related questions in this discussion.

[lzrd]

I have a fedora system that I'd like to run debain-centric builds on. e.g. they use apt or dpkg to check for or install prerequisite packages. Fedora's packages use different package management tools with different package names. (-devel instead of -dev or lopping off "lib" from "libfoo-dev")
I'd also like to make sure that build and test environments are minimal and reproducable. I could use docker, etc. but you are already familiar with those arguments.

[parke]

I have a fedora system that I'd like to run debain-centric builds

Assuming the Fedora kernel provides all the features Lxroot requires (which I think is very likely), this should be pretty easy.

Try the following:

1. Download the Debian Live ISO of your choice.
2. Extract the .squashfs file from the ISO. I use 7z.
3. Extract the .squashfs file to your filesystem. I use unsquashfs.
4. You may need to remove the /etc/resolv.conf file.
5. To run apt to install build dependencies: lxroot -nw $newroot -- fakeroot apt-get build-dep $package.
6. To build packages, try lxroot $newroot and then try to build the package.
7. To install your built package, again use lxroot -nw $newroot -- fakeroot dpkg -i file.deb.

I'd also like to make sure that build and test environments are minimal and reproducable.

To build minimal environments, instead of using the Debian Live ISO, try using my mk-deb.sh script.

https://github.com/parke/lxroot/blob/master/aux/mk-deb.sh

I wrote this script as an alternative to debootstrap, as debootstrap requires root access.

My private version of mk-deb.sh seems to be dated 20231027, which is 20 days later than the version on GitHub. I'm not sure what the difference are, but I may be able to check at some point.

In terms of reproduciblity, use whatever you prefer. Set up your own OverlayFS filesystems, use tar to compress and archive your directory, use BTRFS or ZFS snapshots. Another possible option: modify mk-deb.sh to pull packages from your own private package repository.

If you use minimal environments, you may find that not all dependencies are specified in the Debian .dsc files. Some .dsc files may assume that certain base packages are installed. Not a huge problem, but you may encounter it.

For your use case, I think version 0.22.1 of Lxroot should be sufficient.

Please let me know if you encounter any problems or have any other questions.

[parke]

I looked at the unpublished 20231027 version of mk-deb.sh, and diffed it with the published 20231007 version. I think there is a good chance the older, published version will work. The new, unpublished version depends upon my (also unpublished) xbash framework. Consequently, if I publish the new version, I'd also need to figure out how to publish xbash. Which is probably straightforward, but is more work than simply publishing one file.