Hack-A-N900/First Steps

WARNING: That's where the pleasure and pain of N900 starts. How much pleasure and/or pain depends highly on how familiar you are with linux. So make sure you know how to accomplish simple administrative tasks via a root shell without bricking your system and do regular backups.

Root Access

Start "Application Manager", install package "rootsh" and "OpenSSH Client and Server"

Open "X-Terminal" on your N900.

Gain root access:

sudo gainroot

Add extras-testing to /etc/apt/sources.list

deb http://repository.maemo.org/extras-testing/ fremantle free non-free
deb-src http://repository.maemo.org/extras-testing/ fremantle free

Update apt cache:

apt-get update

USBIP

Connect the n900 via usb to your pc and select "PC Suite Mode".

On your N900:

ifup usb0
ifconfig usb0 192.168.99.2

On your PC:

ifup usb0
ifconfig usb0 192.168.99.1

Please refer to http://wiki.maemo.org/N900_USB_networking for a complete guide.

OpenSSH

Install OpenSSH client and server:

apt-get install openssh

Generate ssh key:

ssh-keygen

From this point it's more convenient to work remotely via ssh.

Copy the generated private key to your PC.

scp root@192.168.99.2:/root/.ssh/id_rsa ~/.ssh/id_rsa_n900

Put the public key to the right place:

ssh root@192.168.99.2 "mv /root/.ssh/id_rsa.pub /root/.ssh/authorized_keys"

Log on to your N900:

ssh -i ~/.ssh/id_rsa_n900 root@192.168.99.2

change /etc/sshd_config to denied password authentication:

# Change to no to disable tunnelled clear text passwords
PasswordAuthentication no

Install essential tools

apt-get install bash coreutils-gnu grep-gnu tar-gnu wget vim

Change shell in /etc/passwd to bash:

root:x:0:0:root:/root:/bin/bash
user:!:29999:29999::/home/user:/bin/bash

NOTE: Maemo ignores shebangs for shells and always executes shell scripts in busybox. You need to pass the script explicitly to any other shell:

bash ./test.sh

WARNING: Don't try to relink /bin/sh to /bin/bash. You system won't boot and you will have to reflash the device.

NOTE: Gnu coreutils and gnu grep are prefixed with the letter 'g'. Therefore you need to call

/usr/bin/gls

to use gnu ls. For some third party scripts/builds to work properly you might need to create symlinks for the gnu tools to be used.

Example:

ln -s /usr/bin/ggrep /usr/bin/grep

You might also create bash aliases for gnu utils.

$HOME/.bashrc aliases example:

# alias to gnu ls instead of busybux
alias ls='gls --color=auto'

alias ll='ls -l'
alias la='ls -la'
alias md='mkdir'
alias rd='rmdir'

# aliases to gnu grep instead of busybux
alias grep='ggrep'
alias egrep='gegrep'
alias fgrep='gfgrep'

Update Kernel

Add tesing repositories to /etc/apt/sources.list:

 deb http://repository.maemo.org/extras/ fremantle free
 deb-src http://repository.maemo.org/extras/ fremantle free
 
 deb http://repository.maemo.org/extras-testing/ fremantle free  
 deb-src http://repository.maemo.org/extras-testing/ fremantle free

apt-get update

apt-get install kernel-flasher-maemo kernel-modules-maemo

cross your thumbs now.. (you backed up before right?)

reboot

WELCOME TO YOUR UPDATED SYSTEM THAT SUPPORTS UNIONFS \o/!

Create unionfs / chroot overlay filesystem for development

Create a 2 GB file on /home/user/MyDocs/sandbox/fs.img

 mkdir /home/user/MyDocs/sandbox/
 cd /home/user/MyDocs/sandbox/
 dd if=/dev/zero of=fs.img bs=1M count=1 seek=2048
 mkfs.ext2 fs.img

Get the shiny overlay/chroot shellscript

 wget http://metalab.at/wiki/images/d/d8/Chroot-unionfs.sh  WARNING the link might be different now look here: Datei:Chroot-unionfs.sh
 mv chroot-unionfs.sh /sbin/chroot-unionfs
 chmod +x /sbin/chroot-unionfs

This script doeas some magic including

• loading the dm-loop kernel module (for /dev/loop? devices)
• overlaying the unionfs filesystem
• mounting all needed filesystem folders inside the unionfs
• chroot()'ing inside

It is started like this:

bash /sbin/chroot-unionfs -v -t /home/user/MyDocs/sandbox/fs.img

Read the source to find out about command line parameters like -t for testing and others..

If this script is successful you should find yourself in a chrooted environment inside the unionfs

touch /CHROOTED
ls /CHROOTED    # it should be here!
exit
 ls /CHROOTED   # it should be gone!