Booting linux system from chroot: is there a better way to do this?

Question

I want to set up Grub menu entry to boot into chrooted system (installed chrooted debootstrap to avoid touching existing system too much).

Currently I do the following to attain it:

1. Install linux-image and friends inside chrooted environment

2. Manually remaster initramfs to chroot into the system instead of usual behaviour:

rootmnt=$rootmnt/root/squeeze
...
#exec run-init ${rootmnt} ${init} "$@" <${rootmnt}/dev/console >${rootmnt}/dev/console
exec chroot ${rootmnt} ${init} "$@"  <${rootmnt}/dev/console >${rootmnt}/dev/console

3.. Add entry to /boot/grub.cfg:

menuentry 'Chrooted debian Squeeze' {
    ...
    linux   /root/squeeze/boot/vmlinuz root=... rw
    initrd  /root/squeeze/boot/initrd-chroot
}

It works but not easy to set up and needs manual hacking every time initrd should be changed. How to do it better?

Answer 1

Why did you switch from run-init to chroot? You shouldn't do that. run-init deletes everything in the initramfs root, then chroots to $rootmnt. You want to keep that behavior.

As for how to avoid having to manually rebuild your initramfs each time, edit the master copy of the init script in /usr/share/initramfs-tools. That should at least work until you upgrade the initramfs-tools package.

A permanent solution would be to patch the init script to recognize a boot argument to append something to rootmnt, and submit that patch for inclusion into debian. Then you can add the argument to grub for entries that should be booted that way.