Category Archives: ARM

Chroot Ubuntu 14.04 on Android (Nexus 10)

I previously had this tutorial for Ubuntu 12.10 on a Padfone and a Nexus 10. I’ve updated it for Ubuntu 14.04.

In this guide, I used http://ports.ubuntu.com/ubuntu as the repository for the bootstrap. However, I ran into some problems and had to retry the installation several times, and ports.ubuntu.com was somewhat slow for me, so I mirrored the trusty armhf repository at http://jtpool.tan-ce.com/ubuntu. I give no guaranties about its uptime or freshness, but if you’re near me (Singapore), you could give it a try to speed things up.

In general, Ubuntu 14.04 doesn’t install as cleanly as 12.10 did, but I believe it should still work. In future, I may have to switch to another distro. Perhaps Arch.

This tutorial documents the steps I went through to get a working Ubuntu system (with LXDE) on my Android device, a Nexus 10. I decided to use the ARM hard-float port (armhf) instead of armle in order to try to extract better performance from the processor.

The tutorial was written based on the notes I made during the process. This tutorial is not for the faint of heart, and it’s best if you have some familiarity with Linux and aren’t afraid of the terminal. I’m not sure if I missed our anything in my notes, so let me know in the comments if anything doesn’t work.

Also, I believe there’s an app that does exactly what I’m trying to do here, but I don’t know if it supports the Padfone yet. If you’re not so comfortable with the terminal, this is probably the way to go.

References
The following were webpages that I found useful. Some even have almost all the steps you need to do this.

Requirements

  • A rooted tablet
  • Terminal Emulator – I like this app because the hardware keyboard on the Padfone dock functions like a PC keyboard, with the back button functioning as escape. Very useful, especially when using Vim.
  • At least 2GB of space on your SD card or internal storage. (Following this tutorial exactly will use 3.5GB)
  • An Linux environment (Might work even on a live CD)

You will also likely need busybox on your tablet

Part 1 – Creating the bootstrap image
We are going to create a filesystem image to contain the entire Ubuntu installation. Then we will copy it to the Padfone.

On your Linux desktop (or server!) ensure you have debootstrap installed:

sudo apt-get install debootstrap

Change directory to a partition with enough space. (3.5G in this tutorial, 2GB minimum) For example:

cd /media/BigDisk

Create the empty disk image file:

dd if=/dev/zero of=img.lubuntu-armhf.root bs=8k count=458752
sudo mkfs.ext4 -L chroot -c img.lubuntu-armhf.root
sudo tune2fs -c 0 img.lubuntu-armhf.root

This creates a 3.5GB filesystem. If you want something smaller, like 2GB, substitute 458752 with 262144. Bear in mind that if you make your filesystem only 2GB, you’ll only have about 200MB free after installing the Lubuntu GUI.

Now, loop mount the newly created filesystem:

mkdir chroot
sudo mount -o loop img.lubuntu-armhf.root chroot

Now begin downloading the core system files.

sudo debootstrap --arch armhf --foreign trusty chroot http://ports.ubuntu.com/

Take a break while it downloads the core files. Once that is done, unmount the filesystem:

cd ../../
sudo umount chroot

Then copy img.lubuntu-armhf.root to your phone.

Part 2 – Setting up the system
Now that we have the bootstrapped filesystem on the phone, we’re going to set it up and install some software packages.

First, open Terminal Emulator, become root, and navigate to the where the image is. For me, my image was in /sdcard/lubuntu

su
cd /sdcard/lubuntu

Now, mount the filesystem, setup a minimal environment, and chroot into it. You will need busybox in order to chroot. In my tablet, busybox is installed in /system/bin-busybox.

export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/system/bin-busybox"
export TERM=linux
export HOME=/root
export USER=root
export UID=0
mount -o loop img.lubuntu-armhf.root lubuntu
mount -t proc proc lubuntu/proc
mount -t sysfs sysfs lubuntu/sys
mkdir lubuntu/dev/pts
mount -t devpts devpts lubuntu/dev/pts
chroot lubuntu /bin/bash

Now that we’re in, let’s finish up the installation:

/debootstrap/debootstrap --second-stage

You’ll notice that a package failed to install – that’s udev. udev in Ubuntu 14.04 performs several checks and will fail, causing apt to fail to install the entire package. To neuter udev so that we can install the rest of the system, run the following command:

dpkg-divert --local --rename --add /etc/init.d/udev
cp /etc/init.d/udev.distrib /etc/init.d/udev

Now, open /etc/init.d/udev in vi, and right after “### END INIT INFO“, enter this line:

exit 0

We also need to neuter initctl so that the fact that upstart doesn’t work does not give us lots of warnings and failures.

dpkg-divert --local --rename --add /sbin/initctl
cp /bin/true /sbin/initctl

Now do some additional basic configuration. (These settings are for my locale, which is English, Singapore. Modify the commands as necessary to match your actual locale.)

locale-gen en_SG en_SG.UTF-8
dpkg-reconfigure tzdata

Set the hostname and DNS server:

echo localhost > /etc/hostname
echo 'nameserver 8.8.8.8' > /etc/resolv.conf

Next, open /etc/apt/sources.list in an editor and replace the contents with this:

deb http://ports.ubuntu.com/ trusty main universe multiverse restricted

deb http://ports.ubuntu.com/ trusty-updates main universe multiverse restricted

deb http://ports.ubuntu.com/ trusty-security main universe multiverse restricted

Now we’ll update the apt indexes, upgrade to the latest versions of all the packages, and finish installing the packages that failed to install during the debootstrap.

apt-get update && apt-get upgrade -y

Ok, let’s get the rest of the software. These are all optional, of course, but I like to have SSH, vim and tmux.

apt-get install ubuntu-standard vim tmux openssh-client openssh-server
apt-get clean
rm /var/run/reboot-required*

If you followed me and installed ubuntu-standard, you’d get another failed package: libpam-systemd. To solve this problem, we’re going to create a dummy init.d script. Create a file at /etc/init.d/systemd-logind with 0755 permissions (executable by all). In this file, enter the following:

#!/bin/sh
exit 0

Then, let apt complete the installation by running “apt-get upgrade -y”.

Ok, now let’s create a non-root user and disable the root password. Of course, replace jack with a user name of your choosing.

passwd -l root
adduser jack
usermod -a -G sudo jack

On Android, users which aren’t part of the AID_INET group (Group ID 3003) will not be able to use IP sockets at all. To get around this problem, we’ll create a group called aid_inet in the chroot with the correct group ID and make the non-root user (“jack”) a member of this group.

groupadd --gid 3003 aid_inet
usermod -a -G aid_inet jack

One last thing, it’s convenient to have a script to be able to get into the chroot quickly. Create a file called enter_chrootand place the following script in it:

#!/system/bin/sh

PREFIX=/Removable/MicroSD
ROOTFS=$PREFIX/lubuntu

if [ ! -d $ROOTFS/etc ]; then
    echo "Mounting lubuntu chroot..."
    mount -o loop $PREFIX/img.lubuntu-armhf.root $ROOTFS
    mount -t proc proc $ROOTFS/proc
    mount -t sysfs sysfs $ROOTFS/sys
    mount -t devpts devpts $ROOTFS/dev/pts
    mount --bind /sdcard $ROOTFS/mnt/sdcard
    mount --bind $PREFIX $ROOTFS/mnt/MicroSD
fi

echo "Setting environment vars"
export TERM=linux
export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
export USER=jack
export SHELL=/bin/bash
export HOME=/root
export LANG=C

echo "Starting shell as user $USER"
/system/bin/chroot $ROOTFS sudo -u $USER -i

This script mounts the filesystems (if they haven’t been mounted) sets up the environment, then enters the chroot properly. Now, to enter the chroot:

sh enter_chroot

The “sh” is necessary because files are not allowed to be executable on the sdcard.

Ok, the command line environment is all done!

Part 3 – Setting up a desktop environment
There are two ways to run a GUI from inside the chroot. Previously, I ran an X11 server in a framebuffer and then used VNC to access it. However, there is now a pretty good X11 server available for Android. I generally use this app. Then all you need to do is install the app, install the “lxde” metapackage, and run “DISPLAY=:0 startlxde”, assuming the app started on display :0.

Note: When I installed lxde, it re-installed libpam-systemd, and two more packages failed. When I purged it (again), those two packages were uninstalled along with it.

That said, if you’re still interested in the VNC on X framebuffer method, take a look at the old article.

Chroot Ubuntu 12.10 on Android (Asus Padfone, Nexus 10)

Updated: Oct 2013 – Non-root users can now use the network, and as a result the VNC server doesn’t need to be run as root anymore.

Updated: Feb 2013 – Made a bunch of corrections and added a few steps

Updated: May 2013 – I bought a Nexus 10, and I’ve moved my Lubuntu chroot over to the Nexus 10. No issues, I’d expect the same steps to work.

This tutorial documents the steps I went through to get a working Ubuntu system (Lubuntu) on my Android device, an Asus Padfone. I decided to use the ARM hard-float port (armhf) instead of armle in order to try to extract better performance from the processor.

The tutorial was written based on the notes I made during the process. This tutorial is not for the faint of heart, and it’s best if you have some familiarity with Linux and aren’t afraid of the terminal. I’m not sure if I missed our anything in my notes, so let me know in the comments if anything doesn’t work.

In this first post, I’ll only cover getting the command line chroot working. In the next post, I’ll cover getting the GUI working.

Update: The steps for getting a GUI are now given in part 3, below.

Also, I believe there’s an app that does exactly what I’m trying to do here, but I don’t know if it supports the Padfone yet. If you’re not so comfortable with the terminal, this is probably the way to go.

References
The following were webpages that I found useful. Some even have almost all the steps you need to do this.

Requirements

  • A rooted padfone
  • Terminal Emulator – I like this app because the hardware keyboard on the Padfone dock functions like a PC keyboard, with the back button functioning as escape. Very useful, especially when using Vim.
  • At least 2GB of space on your SD card or internal storage. (Following this tutorial exactly will use 3.5GB)
  • An Ubuntu/Lubuntu environment (Might work even on a live CD)

I also have busybox on my Padfone, but I’m not sure if it’s necessary.

Part 1 – Creating the bootstrap image
We are going to create a filesystem image to contain the entire Lubuntu installation. Then we will copy it to the Padfone.

On your Linux desktop (or server!) ensure you have debootstrap installed:

sudo apt-get install debootstrap

Change directory to a partition with enough space. (3.5G in this tutorial, 2GB minimum) For example:

cd /media/BigDisk

Create the empty disk image file:

dd if=/dev/zero of=img.lubuntu-armhf.root bs=8k count=458752
sudo mkfs.ext4 -L chroot -c img.lubuntu-armhf.root
sudo tune2fs -c 0 img.lubuntu-armhf.root

This creates a 3.5GB filesystem. If you want something smaller, like 2GB, substitute 458752 with 262144. Bear in mind that if you make your filesystem only 2GB, you’ll only have about 200MB free after installing the Lubuntu GUI.

Now, loop mount the newly created filesystem:

mkdir chroot
sudo mount -o loop img.lubuntu-armhf.root chroot

Now begin downloading the core system files.

sudo debootstrap --arch armhf --foreign quantal chroot http://ports.ubuntu.com/

Take a break while it downloads the core files. Once that is done, unmount the filesystem:

cd ../../
sudo umount chroot

Then copy img.lubuntu-armhf.root to your phone.

Part 2 – Setting up the system
Now that we have the bootstrapped filesystem on the phone, we’re going to set it up and install some software packages.

First, open Terminal Emulator, become root, and navigate to the where the image is. In my case, I copied the image into my SD card, which is mounted at /Removable/MicroSD on the phone. If you copied your image elsewhere, you should change directory there instead.

su
cd /Removable/MicroSD

Now, mount the filesystem, setup a minimal environment, and chroot into it. You will need busybox in order to chroot. In my phone, busybox is installed in /system/bin-busybox.

export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/system/bin-busybox"
export TERM=linux
export HOME=/root
export USER=root
export UID=0
mount -o loop img.lubuntu-armhf.root lubuntu
mount -t proc proc lubuntu/proc
mount -t sysfs sysfs lubuntu/sys
mkdir lubuntu/dev/pts
mount -t devpts devpts lubuntu/dev/pts
chroot lubuntu /bin/bash

If the mount or chroot fails, it’s possible then that busybox is actually required to work. In that case, install busybox and try those commands again.

Now that we’re in, let’s finish up the installation:

/debootstrap/debootstrap --second-stage

Symlink initctl to true so that the fact that upstart doesn’t work does not give us lots of warnings.

dpkg-divert --local --rename --add /sbin/initctl
cp /bin/true /sbin/initctl

Now do some additional basic configuration. (These settings are for my locale, which is English, Singapore. Modify the commands as necessary to match your actual locale.)

locale-gen en_SG en_SG.UTF-8
dpkg-reconfigure tzdata

Set the hostname and DNS server:

echo localhost > /etc/hostname
echo 'nameserver 8.8.8.8' > /etc/resolv.conf

Next, open /etc/apt/sources.list in an editor and replace the contents with this:

deb http://ports.ubuntu.com/ quantal main universe multiverse restricted

deb http://ports.ubuntu.com/ quantal-updates main universe multiverse restricted

deb http://ports.ubuntu.com/ quantal-security main universe multiverse restricted

Ok, let’s get the rest of the software. These are all optional, of course, but I like to have SSH, vim and tmux.

apt-get update
apt-get install ubuntu-standard vim tmux openssh-client openssh-server
apt-get clean
rm /var/run/reboot-required*

Ok, now let’s create a non-root user and disable the root password. Of course, replace jack with a user name of your choosing.

passwd -l root
adduser jack
usermod -a -G sudo jack

On Android, users which aren’t part of the AID_INET group (Group ID 3003) will not be able to use IP sockets at all. To get around this problem, we’ll create a group called aid_inet in the chroot with the correct group ID and make the non-root user (“jack”) a member of this group.

groupadd --gid 3003 aid_inet
usermod -a -G aid_inet jack

One last thing, it’s convenient to have a script to be able to get into the chroot quickly. Create a file called enter_chrootand place the following script in it:

#!/system/bin/sh

PREFIX=/Removable/MicroSD
ROOTFS=$PREFIX/lubuntu

if [ ! -d $ROOTFS/etc ]; then
    echo "Mounting lubuntu chroot..."
    mount -o loop $PREFIX/img.lubuntu-armhf.root $ROOTFS
    mount -t proc proc $ROOTFS/proc
    mount -t sysfs sysfs $ROOTFS/sys
    mount -t devpts devpts $ROOTFS/dev/pts
    mount --bind /sdcard $ROOTFS/mnt/sdcard
    mount --bind $PREFIX $ROOTFS/mnt/MicroSD
fi

echo "Setting environment vars"
export TERM=linux
export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
export USER=jack
export SHELL=/bin/bash
export HOME=/root
export LANG=C

echo "Starting shell as user $USER"
/system/bin/chroot $ROOTFS sudo -u $USER -i

This script mounts the filesystems (if they haven’t been mounted) sets up the environment, then enters the chroot properly. Now, to enter the chroot:

sh enter_chroot

The “sh” is necessary because files are not allowed to be executable on the sdcard.

Ok, the command line environment is all done!

Part 3 – Setting up a desktop environment
There is an X11 server for Android, but as far as I know, there isn’t any window manager for Android yet. So, to get around this little problem, we’ll be running X11 in a framebuffer and use VNC to access this framebuffer.

First, we install the necessary packages. I’m using LXDE, but you could conceivably use something else lightweight like xfce.

apt-get install xvfb x11vnc lxde
apt-get --reinstall install xfonts-base

Next, we’re going to disable the logout feature, as it doesn’t work correctly:

dpkg-divert --local --rename --add /usr/bin/lxde-logout
cp /bin/true /usr/bin/lxde-logout

Now we need to configure startup files for our X11 session. The following listing shows the script used to start the GUI. This script should be run as the non-root user.

#!/bin/bash

# Check if the frame buffer is already running
pgrep Xvfb > /dev/null
if [ $? -eq 0 ]; then
    echo "Xvfb is already running. If you want to kill it, use:"
    echo "pkill -15 Xvfb"
    exit
fi

# Launch the X11 frame buffer
# This geometry is about half the usable resolution on the Nexus 10
# I choose to half it and zoom, because at full resolution, the UI 
# elements are way to small to be usable.
geometry='1280x750x24'

Xvfb -screen 0 $geometry -ac > /dev/null 2>&1 &
export DISPLAY=:0

# Give the server a chance to start up
sleep 1

# Now start the LXDE session
startlxde > /dev/null 2>&1 &

echo "Launched LXDE session"

# Launch the VNC server
x11vnc -localhost -display :0 -forever -usepw > /dev/null

Run this script whenever you want to use the GUI, and use an Android VNC client to open the display at localhost:5900. To kill the GUI, use the following command:

pkill -15 Xvfb

Or just type Ctrl-C in the terminal where it’s running.

Building the GNU ARM Toolchain

Note: This post serves mainly as a reminder to myself. I did not figure out everything myself and got the original instructions from here (many thanks to Adam Kunen). The steps here aren’t exactly the same, but they’re mostly similar. His posts also contain some explanations for the various configure options as well as a short explanation on the triplet (ie. “arm-none-eabi”).

The goal: To build the GCC toolchain for ARM suitable for bare-metal work, complete with gdb and libc (newlib). At the end of the day I used this to compile the LwIP sample projects (both “standalone” and FreeRTOS versions) for an STM32F4 evaluation board.

These are the versions of the various components I used:

There should be no issues using newer versions of these components.

In this tutorial I’m going to install the tool-chain at ~/arm-none-eabi/ with with the sources in ~/arm-none-eabi-src. Do change this path if you prefer a different location. (On my own machine, I placed it in /opt/arm-none-eabi)

Update (6/9/2013): Some of the configure commands include “–with-cpu=cortex-m4”. This is because I was building for a ARM Cortex-M4 MCU. You should replace this with your target architecture. I had problems with an earlier build when I didn’t add this option in. It turns out that Cortex-M processors are picky about word alignment, and if you don’t configure this in before you build newlib and gcc, the libraries may not respect the word alignments and you may end up with hard faults.

Ok, first we create the directory skeleton:

cd
mkdir arm-none-eabi arm-none-eabi-src
cd arm-none-eabi
mkdir src build

Now, download the the packages and extract them:

cd ~/arm-none-eabi-src/src

wget ftp://ftp.gnu.org/gnu/gcc/gcc-4.7.1/gcc-4.7.1.tar.bz2
wget ftp://ftp.gnu.org/gnu/binutils/binutils-2.22.tar.bz2
wget ftp://ftp.gnu.org/gnu/gdb/gdb-7.4.tar.bz2
wget ftp://sources.redhat.com/pub/newlib/newlib-1.20.0.tar.gz

tar -xf gcc-4.7.1.tar.bz2
tar -xf binutils-2.22.tar.bz2
tar -xf gdb-7.4.tar.bz2
tar -xf newlib-1.20.0.tar.gz

Build binutils first:

cd ~/arm-none-eabi-src/build
mkdir binutils-2.22
cd binutils-2.22
../../binutils-2.22/configure --target=arm-none-eabi \
  --prefix=~/arm-none-eabi --with-cpu=cortex-m4 \
  --with-no-thumb-interwork --with-mode=thumb
make all install
export PATH="$PATH:~/arm-none-eabi/bin"

At this point you could also put the path “~/arm-none-eabi/bin” into your .bashrc file if you want.

After this, we will do the first part in building gcc.

Note that gcc relies on three bignum libraries: mpfr, mpc, and gmp. If the version of these libraries on your host are out of date, you can compile against newer version. Just download the source code for those three libraries, rename them to mpft, mpc, and gmp respectively, and move them inside the gcc source tree. Do not compile these libraries separately.

In both cases the steps to build the first stage are:

cd ~/arm-none-eabi-src/build
mkdir gcc-4.7.1
cd gcc-4.7.1
../../src/gcc-4.7.1/configure --target=arm-none-eabi \
  --prefix=~/arm-none-eabi ---with-cpu=cortex-m4 \
  --with-mode=thumb --disable-multilib \
  --with-no-thumb-interwork \
  --enable-languages="c,c++" --with-newlib \
  --with-headers=../../src/newlib-1.20.0/newlib/libc/include \
  --with-system-zlib
make all-gcc install-gcc

Here I deviate from Kunen’s tutorial a little. I could not get gcc 4.7.1 to compile without the “–with-system-zlib” flag. (The make process fails somewhere when it tries to do link tests. If anyone can explain why or knows why using the system zlib is disadvantageous, do leave a comment and let me know.)

Okay, now let’s build our newlib libc with our freshly compiled gcc cross compiler:

cd ~/arm-none-eabi-src/build
mkdir newlib-1.20.0
cd newlib-1.20.0
../../src/newlib-1.20.0/configure --target=arm-none-eabi \
  --prefix=~/arm-none-eabi --disable-multilib \
  --disable-newlib-supplied-syscalls
make all install

Here there’s another configuration option which I added which Kunen doesn’t: –disable-newlib-supplied-syscalls. The reason is I want to supply the system call stubs myself so I can have a potentially fully functional stdin, stdout, etc. Also, if you’re using an RTOS, here is where you could make standard libc malloc work with your RTOS’ memory management (I think… haven’t tried this yet).

The catch is you’ll always need supply the system call stubs if you use printf, and friends, or malloc and friends. You can read more about it here and here.

Now, we can complete the gcc build:

cd ~/arm-none-eabi-src/build/gcc-4.7.1
make all install

And the final piece, gdb:

cd ~/arm-none-eabi-src/build
mkdir gdb-7.4
cd gdb-7.4
../../src/gdb-7.4/configure --target=arm-none-eabi \
  --prefix=~/arm-none-eabi
make all install

Alright! Now put

export PATH="$PATH:~/arm-none-eabi/bin"

in your .bashrc or /etc/environment (if you haven’t already) and you have a fully functional ARM tool-chain suitable for bare-metal work.