modular-debian

MoDe - modular debian (originaly mini-debian)

Idea

I love Linux live distros, mainly Knoppix. But it's not so fun, if such a distro runs on broken CD/DVD drive or on old DVD/CD-RW medium or on not so fast USB flash.

I know there is a SLAX, brilliant Idea for modular Linux. It is live OS too, and it is minimalistic (runs on 48MB RAM or 256MB for KDE).

But:

• SLAX is based on Slackware, I use Debian.
• For installed (non-live) system Debian Linux requires about 200MB too. That's OK. However every server or PC has today at least 2GB RAM, even PC Engines APU2 has 2GB or 4GB and can run even ESXi. So I have plenty of RAM available
• I want to start Linux without need of some special medium (CD, DVD, USB). The best way is to start from Network. (NFS is one solution, but it needs NFS server, permanent access to this NFS server, not the same as live-OS)
• I wanted to create something very fast and easy to prepare.

So:

I have seen the code in the linuxrc script in initramfs of Debian. They make

mount -t $ROOTFSTYPE $ROOTFLAGS $ROOT /target

What if there is a ext3/4 file image with some base debian system (created using debootstrap + few important packages) included in the initramfs? Then I could set ROOTFSTYPE=ext3, ROOTFLAGS=loop and ROOT=/debian.img and it should mount this file using loop device. Steps to prepare:

• Create file image with debian basic system using debootstrap - easy+fast
• Install a few important packages in this file image using mount -o loop, chroot and apt-get - easy+fast
• Copy this image file to initramfs - easy+fast
• Run kernel with modified initramfs from Grub, Syslinux (ISOlinux, PXEboot i.e. from network) - easy+fast
• This will load and store the big image in RAM, but 200MB of 2GB is nothing.

OK, it was done really easy and fast. But of course it was not perfect:

• The initramfs was big, containing whole Debian system (of course gziped cpio, but still a few MB) - pxeboot needs a few minutes to download initramfs from tftp server.
• After start, root FS is RO, many services expect some writable non-tmpfs persistent folders.
• Unable to do temporary local changes in config files, unable to install new packages.

Then came the idea. System based on Debian, on standard tools included in initramfs with as few as possible extending scripts to allow get file image (either during tftp download together with Linux kernel and initramfs or using busybox wget to get the image from webserver running on tftp server) created as squashfs with Debian system and mount this image into AUFS/UnionFS as rootfs (this looks like what SLAX do). Then I have written first script for preparing and update Debian image files for Squeeze and Wheezy, and some scripts to mount this squashfs image to aufs. I have versions for i386 and amd64, console-only and with LXDE. It means total there are 8 different images with mostly the same packages (console version and X version contain the same command line tools).

Later I needed to have some basic system and create some extending images to give more features and fixed configuration. I have updated the scripts to allow downloading and merge-mounting multiple images. Now it looks really like SLAX.

So I wanted to make new script which would create modular system.

Design

As base image will be used debootstrap image. SquashFS will be created. This is the only image which will be created without aufs and underlaying squashfs images.

The second image essential will contain some important basic packages, e.g. kernel, aufs-tools, squashfs-tools, to allow run the base image. Creating this image means to mount base squashfs image to aufs mount, install this extending packages and create second squashfs only from the changed branch (RW branch) of aufs.

The next images will be based on some existing modules, e.g. for console image the base squashfs image and essential squashfs image will be mounted to aufs, together with empty RW branch. In this mounted aufs will be installed console tools and created configuration. From this RW branch will be created squashfs image console.

On the console image (and the lower images) can be based the lightx image, with only light WM, e.g. LXDE, and web browser. On lightx image can be based fullx image with libreoffice, gimp etc.

The images will be big, but then you have surely at least 8GB RAM for fullx image.

The images will be downloaded to RAM, mounted each as simple squashfs and then all together mounted to aufs. The RW branch of aufs will be mounted to tmpfs somewhere to rootfs so the user can generate own squashfs from currently running system and then download next time.

Now how to specify the order of images. My idea is to assign shot name for every level and the image name with names from 1st level to nth level, e.g.:

• first level image is base
• second level image is essential, i.e. whole image name is base-essential.sqfs.img
• third level image is console, i.e. whole image name is base-essential-console.sqfs.img
• fourth level image is lightx, i.e. whole image name is base-lightx-console-essential.sqfs.img
• there can be other fourth level image named smtp working as SMTP server with fixed config, based on console image, i.e. whole image name is base-essential-console-smtp.sqfs.img

And so on. There is no limit on level depth and which images are the images based on.

If the underlaying image will be updated, all images based on this image should be recreated too, but not required, in case that some image contains only configuration files. To recreated the image means to mount underlaying images to aufs and do changes - install new packages, create/modify some files.

This "project"

I want to create hopefully a few simple scripts to be able easy and "fast" to create these images.

One script should create and update the images.

Other scripts (and maybe configuration files) should do downloading and mounting the images. Some of them I can take from the old version.

Maybe I will add the possibility to mount NFS folders or local drives, which could simplify storing own configuration or use same home folder. Or maybe to connect home/working folder over sshfs. But these are only ideas and uncertain future.

Important note

I have created this project mainly for me. I want to create this script. But I have not enough time for this "project". But this "project" is and will be released under GNU GPL so you can take, modify and distribute it. If you will find this "project" interesting and you will want to participate some day, of course you can send me some updates, but I am not sure, if I will have enough time to merge them. So maybe you will prefer clone, develop and release your own version.