Convert from Ubuntu to Debian LIVE

Convert from Ubuntu to Debian LIVE

The following will walk you through setting up a chroot on your live system, updating it to include the software you need to replace your live system, overwriting your live system, and rebooting into your new Debian based system.

The debian base debian system will be set up via debootstrap.

export $CHROOT=/path_to_chrootapt-get install debootstrap

You are ready to run debootstrap This command will take a while as it is downloading and installing a base system. Sit back and relax.

Installing the chroot with debootstrap

sudo debootstrap --arch amd64 sid $CHROOT http://http.debian.net/debian/

You will need to determine what your systems architecture is, you can do this by executing uname -p

Entering the chroot

In this section mount points will be set up to refer to similar places on your current live system. These are mainly pseudo filesystems like proc, sysfs, etc. Instead of mounting them manually inside of the chroot a mount bind is used for persistence.

Perform the following as root.

sudo mount --bind /proc $CHROOT/proc

sudo mount --bind /sys $CHROOT/sys 

sudo mount --bind /dev $CHROOT/dev 

sudo mount --bind /dev/pts $CHROOT/dev/pts 

sudo mkdir $CHROOT/old_root 

sudo mount --bind / $CHROOT/old_root 

# Copy files over to the chroot 

sudo cp /etc/resolv.conf $CHROOT/etc/resolv.conf 

sudo cp /etc/fstab $CHROOT/etc/

Get the packages from your old system and install them on your "new" install

sudo dpkg --get-selections | sudo tee $CHROOT/packages

Enter the chroot

sudo chroot $CHROOT

Installing and setting up the new system

This section walks you through updating your system to look as similar as possible to the previous system you had set up. This can be skipped if you arrived here looking for a way to overwrite your live system using any sort of chroot (stage3 gentoo, fedora chroot etc), you may skip this section.

*At this stage you should be inside the CHROOT.

Install dselect and initialize its database

apt-get install dselect 

dselect update

Now, take a moment to look at the packages file we created in the root of your sysroot /packages. Packages that no longer are necessary or undesired can be removed from this file.

Ubuntu uses a different init system, upstart, than Debian, sysvinit. To ensure that upstart does not remove sysvinit find the line in packages that says:

upstart                     install

Remove it.

After saving any modifications to packages, it is time to use the package file to set packages to install.

Still in the CHROOT

dpkg --set-selections < packages 2> dead_packages

dead_packages are packages that did not match up with any of the available packages in debian.

They are identified by lines like:

dpkg: warning: package not in database at line 653: libppl-c2

These are packages worth noting for later so they can be installed by hand.

Run the dselect upgrade command and wait for all the packages to be installed:

apt-get dselect-upgrade

Daemons not starting

After the dselect-upgrade has completed a number of daemons will most likely not be able to start. You have two options, remove the daemons for now or iteratively disable the daemons on the currently live system so the ports are available for the newly installed ones to start.

To iterate over the items that need repair use apt-get -f install. The process is more or less.

1. Find daemon with a problem (mysql)
2. Stop daemon on live system (/etc/init.d/mysqld stop)
3. Continue apt upgrade process in chroot (apt-get -f install)

Example of what this may look like:

Errors were encountered while processing:
mysql-server-5.5
mpd
mysql-server
E: Sub-process /usr/bin/dpkg returned an error code (1)

Configuring your Chroot

In order to be able to use the newly created live system a few things will need to be set up properly.

1. A kernel and bootloader need to be present
2. Networking needs to be set up
3. User account/root password

Install a kernel and a bootloader

If you used the dselect upgrade method above a bootloader is most likely already installed, however, chances are low that a kernel is installed.

apt-get install linux-image-amd64 grub

Notice the amd64, again pay attention to the architecture you want to install.

Setup a root password/Addusers

Users need to be set up so that the new debian system is accessible once booted. It is not necessary to add users now but at the very least a root password needs to be set.

In the chroot the default user is ‘root’ run passwd to set up a password

To add users use adduser <username>

Setting up networking

debootstrap by default will not setup networking and a server without networking is of little help when the machine is remote.

Add the following to /etc/network/interfaces

auto eth0 allow-hotplug eth0  

iface eth0 inet dhcp

If the default ethernet device is not eth0 replace it with the proper device. If you are unsure run ifconfig or ip link show on the current system and look for your current IP Address.

***Make sure openssh-server is installed on the system.

Taking over the live system

The majority of distros are not exactly binary compatible so it is not possible to simply move part of the sysroot out of the way. All of this has to be done at the same time via the chroot.

Remember the old system is mounted in the chroot under $CHROOT/old_system, this was performed above in the Entering the Chroot section.

Once these steps are started it is difficult to turn back.

mkdir old_root/old && cd old_root && mv * old

The above mv command will not complete without a few failures or warnings like

mv: cannot move 'sys' to 'old/sys': Device or resource busy, this is OK. The directories are used by the new system and it is due to a FS or PseudoFS being mounted on that location.

Now copy the new system over, this is still within the chroot!

cd / ; rsync -a bin boot debian dead_packages etc initrd.img lib lib32 libx32 lib64 media mnt opt packages root sbin var vmlinuz run usr var vmlinuz old_root/

*Note: You may see errors about rsync not being able to link_stat some files. This can safely be ignored.

Finalizing

Make sure your fstab points at the proper system.

install grub on your device

/usr/bin/grub-install /dev/sda

Regenerate grub’s config 

/usr/sbin/update-grub

That’s it, reboot your system and hope for the best. If you get stuck somewhere post a comment and I’ll help where I can.

Potential problems

Q. When entering the chroot the old_root was not available?
If this happens you can mount the root device within the chroot as if it is a normal block device

mount /dev/sda1 /old_root

Where /dev/sda1 is the root device from your currently booted system. 

References

https://wiki.debian.org/Debootstrap