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[Avancé] Installer Debian Gnu/Linux via loop et chroot

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Salut, je partage un tuto que je viens d'ecrire.

Il en existe probablement une centaine déja de tuto de ce style mais je voulais comprendre et noter mes etapes.

Dans android et le market, il me manquait vraiment trop d'outils de base du monde gnu (la couche applicative qui tourne sur Ubuntu, debian, Fedora, etc..). Notamment pour moi des langages de développement (perl, python,..), serveur web robuste, .. des centaines de choses en fait.

Attention, ce tuto ne comprend pas la partie XWindow donc le resultat sera "tout en console". Pour avoir un vrai système graphique avec gestion parfaite du touchpad et que le clavier qu'on a dans android apparaisse aux bons moment, c'est probablement pas aussi direct et spécifique à chaque telephone/tablette.

Il faut un ordi qui a debootstrap (Ubuntu et Debian l'ont, je conseille toujours Debian)

Ce tuto permet aussi d'installer une ubuntu, il faut remplacer 'sid' par la distro qu'on veut.

Distributions disponibles:

breezy dapper edgy etch feisty gutsy hardy hoary hoary.buildd intrepid jaunty karmic lenny lucid maverick natty oldstable oneiric potato precise sarge sarge.buildd sarge.fakechroot sid squeeze stable testing unstable warty warty.buildd wheezy woody

Les explications sont en anglais mais les commandes sont internationales :)

Si vous rencontrez des problèmes, je pourrai essayer d'y repondre.

On the device, you will need

  • a kernel with loop support (otherwise, you need a standalone ext2/3/4 partition) and
  • gnu/posix commands , it can be through busybox. You need at least:
    • chroot (built for this architecture, if not you can find one ARMel in debian repositories)

(busybox is there if you have sshdroid that you can download for free in the market, fsck is also there)

On your computer, you need a few things to prepare your image (but its possible to do everything on the tablet if you search a bit) To bootstrap, you will need a machine with debootstrap, can be found in debian or ubuntu at least. This will install a debian system with the target architecture in a directory.

On your computer:

#create loop file. this is a "disk partition in a file"
#the following line create a 600MB image, adapt to your needs
dd if=/dev/zero of=debian.img seek=599999999 bs=1 count=1

#format the disk partition with a filesystem of your choice (it needs unix permissions and ability to have exec, bind, ..)
mke2fs -F debian.img

#mount the new partition to a directory
mkdir debian && mount -o loop debian.img debian

#Install debian sid. Adapt to your needs:have a look at debootstrap manpage to see all distribution available.
#All ubuntu and debian (goes back to woody) are available. I recommend debian and I use sid, name for unstable branch
#We do it in 2 times using --foreign
debootstrap --verbose --arch armel --foreign sid debian http://ftp.fr.debian.org/debian

#Unmount to send image to the device
umount debian

We now have a portable ARMel debian unstable filesystem in the file debian.img (not fully configured for users and network and not including /boot like kernel, and virtual directories like /dev, /sys, /proc etc..)

Now we will send image to device. we will store our debian on the external SD, adapt to your needs Even if the external SD is in FAT, the included filesystem, in this file will be the one you have chosen before ext2/3/4 In the following, my SD Card is in /mnt/external1, change the steps to fit your setup!

Send to the device

scp debian.img root@

Connect to the device to finish install overthere

ssh root@

Mount the disk. The debian virtual disk will be mounted to the android /data/local/mnt

#Create target directory if not already existing
mkdir -p /data/local/mnt && cd /data/local

#Mount the loop disk. We use noatime so that the external sd is not synced too often to keep lifetime of external SD  
mount -o loop,noatime -t ext2 /mnt/external1/debian.img mnt/

#Use Chroot: this will change your current shell / to point to /data/local/mnt
#The kernel is still the one you are running..

#Finalize with second stage of debootstrap
chroot mnt/ /debootstrap/debootstrap --second-stage

We will now finish to configure the debian system: apt-get, users, network

#Set apt-get to get packages from sid repository. Adapt to your needs
echo 'deb http://ftp.fr.debian.org/debian sid main' > mnt/etc/apt/sources.list
#Set network server to use for resolving names to IP (like debian.org when using apt-get)
#We use here google NameServer
echo 'nameserver' >mnt/etc/resolv.conf
#This is a detail but there for safety reason. With this, when you are within your debian, your prompt will be
#It can be interesting to know wether you are in android or in debian to avoid doing stupid mistakes particularly with rm ;)
echo debian > mnt/etc/debian_chroot

To have this special prompt, colours and for a few alias, in mnt/root/.bashrc, uncomment some lines to have this:

# ~/.bashrc: executed by bash(1) for non-login shells.

# Note: PS1 and umask are already set in /etc/profile. You should not

# need this unless you want different defaults for root.

PS1='${debian_chroot:+($debian_chroot)}\h:\w\$ '

# umask 022

# You may uncomment the following lines if you want `ls' to be colorized:

export LS_OPTIONS='--color=auto'

eval "`dircolors`"

alias ls='ls $LS_OPTIONS'

alias ll='ls $LS_OPTIONS -l'

alias l='ls $LS_OPTIONS -lA'


# Some more alias to avoid making mistakes:

# alias rm='rm -i'

# alias cp='cp -i'

# alias mv='mv -i'

We will now again change / to point to /data/local/mnt and execute bash inside this

You are now in your new debian system

chroot mnt /bin/bash

#chroot included in android (not the one from busybox) is very limited so you always have to login again to get all system variables set
/bin/su -
cat /etc/debian_version

For minimal tty support (for ssh and screen at least) you will need pts. /proc is needed for any linux to get process and kernel informations exported by the kernel and /sys is the same regarding your HW config

#Mount devpts, proc and sysfs filesystem. The system will now where to find information from the running kernel.
mount -t devpts devpts /dev/pts
mount -t proc proc /proc
mount -t sysfs sysfs /sys

With this, you are sharing pts, proc and sys with your android so don't be surprised if you run ps to see also android processes. You are not anymore using your gnu commands with limited busybox, you are running a complete debian system with all options!

/bin/su -
#we might want to see all real partitions of the android system from within debian
#this is not always needed. We will link to the knowledge our kernel has of our disks
rm /etc/mtab
ln -s /proc/mounts /etc/mtab

#setup a password for root
<enter twice your new root password>

You now have a complete, configured debian system running with architecture ARMel.

Thanks to the debian team for making such amazing tools.

You can go further and install gnome. An easy way then to connect to it is through vnc:

your debian will have the desktop "exported" to a network connection through x11vnc, and with android vnc viewer, you connect to it

the problem is it will be slower than direct window system and

keyboard, mouse, etc.. is specific to your device

in debian you will find several virtual keyboards. experiment youself.

Everytime you reboot, you will loose mount points. You can create this script to execute to get in the chroot wether or not you rebooted Put it in /mnt/external1/debian.sh Everytime you want to start debian, make sure you are root and call it with "sh /mnt/external1/debian.sh" (without quotes)

cd /data/local

#these four lines will return warnings if the mounts are already there if you did not reboot

#(device busy) Ignore this

mount -o loop -t ext2 /mnt/external1/debian.img mnt/

mount -t devpts devpts mnt/dev/pts

mount -t proc proc mnt/proc

mount -t sysfs sysfs mnt/sys

#Start Debian

chroot mnt /bin/bash

#Unmount Debian and remove loop

#Android umount does not allow multiple mountpoints, only busybox so we do it in 4 commands

cd /data/local

umount mnt/dev/pts

umount mnt/proc

umount mnt/sys

umount mnt

losetup -d /dev/block/loop0

In debian, start a new login shell if HOME is broken

/bin/su -

Manually stop debian if needed

#until you should see your prompt without the (debian) meaning your are out of debian
cd /data/local
umount mnt/dev/pts
umount mnt/proc
umount mnt/sys
umount mnt
#remove the loop link. adapt if you already had several loops, here only one means I got loop0 during the first mount
losetup -d /dev/block/loop0

Avoiding mistakes Its not a good idea to work in your debian as root, so create a new user

#Be sure to be in debian system not android!

(debian):~#adduser toto
#... give password and confirm with Y

#create a group to allow users to use network sockets
addgroup --gid 3003 sockets
usermod -G sockets -a toto

#then everytime you want to start debian, run the script like before but login as user (add toto at the end)
/bin/su - toto
#you can then play with sudo to gain root if you really need

(debian)toto@localhost:~$ perl -e 'print "Have fun!\n"'
Have fun!

Edited by gaffy4141
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