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schroot for Mageia

To easily manage single or multiple chroot environments, schroot, a sophisticated and highly flexible change-root management tool, may be employed. I'm most interested in first using schroot to test beta versions of Crossover.

Chroot jails are commonly employed to add an additional level of security to some Linux services like ftp or http servers. If an attacker gains control of the server, he is trapped in the chroot jail and cannot easily harm the entire system. As well, chroot is often employed in a "rescue" mode where Linux is launched from a DVD of CD and the damaged root filesystem is run from a chroot environment to make repairs easier.

To see how a chroot environment for Mageia is created, refer to the Chroot HOWTO in the Mageia Wiki.

Mageia appears to have incorporated schroot from Debian because it makes for building and testing RPMs easier when they also use iurt.

Since schroot was initially developed on Debian systems, much of the technical information is focused on that particular distribution of Linux. Even the example configuration file is written for Debian and no one has bothered to change it for Mageia.

One of the benefits of schroot is that you can easily install different versions of your chroot environment and start with a clean install. Using the unionfs system, you can have a consistent base environment and install development libraries on top of that, then easily delete the build environment leaving a clean basesystem. In fact, this is just how the Mageia distribution is done, using an application called iurt to manage the build and schroot to create the build environment needs for each package.

CHROOT
HOWTO Create a chroot Cauldron environment lays down the basics of installing a baseline Mageia install.


NOTE - To avoid the hassle of manually finding a Mageia repository, modify the CHROOT HOWTO's instruction with info from the URPMI HOWTO as follows:
$ sudo urpmi.addmedia --distrib --mirrorlist '$MIRRORLIST' --urpmi-root /media/chroot/mageia



You can install new packages from outside the chroot environment for example, by using --urpmi-root /mnt/chroot/mageia32. Alternatively, chroot into the environment and used the urpmi command as normal.

To launch a graphical desktop from the chroot environment is a little tricky. You need to provide the chroot with its own xserver, but not in the way you have an X server in your normal environment. The Ubuntu Help Community provides a good example as well as the Mageia wiki. Taken from there: 

Using Xnest

Install Xnest into your running host system urpmi x11-server-xnest $ sudo urpmi x11-server-xnest

Run the following command outside the chroot: 
$ Xnest -ac :1 

Then enter the chroot and load your graphical application as in the following example:
$ export $DISPLAY=localhost:1 $ /usr/bin/mozilla

Using XEPHYR

There is also Xephyr, a kdrive server that outputs to a window to a pre-existing X-server. From the same Mageia Wiki page:

Install Xephyr package into your running host system
$ sudo urpmi x11-server-xephyr
Run the following command outside the chroot:
$ Xephyr -ac :1
Then enter the chroot and load your graphical application as in the following example:
$ export DISPLAY=localhost:1 $ /usr/bin/mozilla 
 

Conclusion

Although this will take some more experience on my part to use it correctly and then I can just script it.

Starting from scratch like this is a good way of seeing if there are any packages that Crossover needs to run that are not installed for some reason.

The ultimate target for me and schroot is source-roots, or chroots with a union-type file system. There is an underlying filesystem that never changes with any modifications made disappearing upon exit.

What I would suggest is that your base system would be everything necessary to launch your app (Crossover in my case) and then delete that app and use the base for a union-filesystem schroot. Then as updates occur, you can always test them against a system known to work and not have to involve you daily desktop/laptop, run a virtual machine, or keep a spare computer.

RESOURCES
chroot HOWTO in the Mageia Wiki


schroot Debian Wiki

debian chroots with schroot

schroot- Richard Darts - Debian Wiki

schroot - chroot for any user

schroot manpage

MaximumHoyt Mageia chroot HOWTO

Iurt Mageia Wiki

Mageia Bug Report

How to start Xorg-server inside plain chroot?

Accessing graphical applications inside the chroot




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Comments

Unknown said…
I enjoyed this blog post. It was inspiring and informative. You can also check about chroot Xorg from elstel.org
2/14/2022 11:41 PM
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