QEMU User Mode on Ivon's Blog

Use debootstrap on x86 to create an ARM rootfs and install a chroot Debian environment on Android

infoivonblog.nkfjt@aleeas.com (Ivon Huang) — Thu, 16 Nov 2023 23:00:00 +0800

According to the Debian Wiki, debootstrap is a wrapper script that can produce a minimal Debian or Ubuntu rootfs (root filesystem) according to personal preference. It is suitable for people who want to set up Linux from scratch themselves, installing a Linux system in a way similar to Arch Linux’s pacstrap.

But that is not my purpose here. I want to move the completed rootfs to a phone for chroot or Termux proot use, and run a Debian environment on the phone.

I will use a Linux computer to create the Debian rootfs. Since the computer is x86_64, I need to use the QEMU emulator in order to enter an ARM64 chroot environment on the computer.

If you do not want to use a computer, then take a more roundabout route: first install chroot Ubuntu on the phone, then install debootstrap inside it to create the Debian rootfs. This method does not need QEMU translation, but it cannot be done through a rootless Termux environment.

Install the debootstrap package; most Linux distributions include it. As for installing arch-linstall-scripts, that is because it provides the useful arch-chroot script

sudo apt install debootstraparch-linstall-scripts

To create an ARM rootfs on an x86 computer, we need to use the qemu-user-static tool to emulate the ARM64 instruction set

sudo apt install qemu-user-static

Confirm that the binfmt service is enabled

sudo systemctl enable --now systemd-binfmt.service

Create the Debian rootfs directory

cd ~/Downloads
mkdir debian

Start creating the Debian 12 Bookworm rootfs, downloading packages from the Taiwan Debian server

sudo debootstrap --arch arm64 --components=main,universe bookworm debian12 http://ftp.tw.debian.org/debian/

After installation, first put qemu-aarc64 into the rootfs, so it will automatically translate instructions

which qemu-aarch64

sudo cp /usr/bin/qemu-aarch64 debian/usr/bin

Chroot into it and do some initialization. When using arch-chroot, you do not need to manually mount /proc and such; everything is handled automatically

sudo arch-chroot debian

Use cat /etc/os-release to confirm that it is a Debian system
After configuring it, exit chroot

exit

Compress the rootfs into a tar.gz

sudo tar -zcpf debian.tar.gz debian/*

Send it to the Android phone with ADB and extract it on the phone.

The process of installing a desktop environment is similar, so I will not repeat it. The steps involving commands below can also be completed first on the computer described above.

If the phone has root privileges, refer to chroot Ubuntu

If it does not have root privileges, refer to Termux proot for installing the desktop environment.

Use Termux qemu-user to emulate x86_64 Ubuntu on ARM64 Android

infoivonblog.nkfjt@aleeas.com (Ivon Huang) — Thu, 16 Nov 2023 18:00:00 +0800

This explains how to emulate an x86_64 Ubuntu system on an ARM64 (Aarch64) Android phone through Termux proot-distro.

1. Explanation
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You may say: most Android devices are ARM64, right? Why not just install the ARM version of Ubuntu? Some programs are just obnoxious and are not compiled for ARM.

So on the road of force-running x86 programs, we have three choices:

Run an ARM64 system and install the Box64 translator
Use qemu-system to start a complete x86_64 emulator, such as Ubuntu x86_64 + QEMU
Use qemu-user to emulate an x86_64 system.

qemu-system runs a virtual machine, emulating complete hardware devices so Linux can run as if it were on a real computer. Of course, it consumes a lot of resources.

qemu-user, on the other hand, is a userspace emulator that can emulate x86 executables on ARM64 devices without needing the resources of an entire virtual machine.

QEMU supports emulating many architectures. Besides x86_64, emulating 32-bit x86, RISC-V, and other architectures is also possible.

In Termux, as long as we have a rootfs, we can get a Linux system running without using qemu-system virtual machine emulation.

The proot-distro tool has built-in qemu support. This article discusses using the proot-distro tool together with qemu-user to run an x86_64 system.

Because it is emulated, program execution is naturally slower than native. Add proot’s performance overhead and it becomes even slower. At the end of the article, we will compare the speed of Proot native vs Box64 vs qemu-user.

2. Test environment
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Phone: Sony Xperia 10 V, Android 13
Linux kernel version: 5.4
Termux version: 0.118.0
qemu-user version: 8.1.0
Ubuntu version: 20.04 (Ubuntu 22.04 runs into a problem where apt pub_key cannot be imported)

3. Create an x86_64 proot Ubuntu
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Refer to proot-distro rootfs and add the Ubuntu 20.04_x86_64.sh script. But here we need to change the content a little.

vim $PREFIX/etc/proot-distro/ubuntu20.04_x86_64.sh

Modify it as follows

# Specify the architecture as x86_64
DISTRO_ARCH=x86_64

DISTRO_NAME="Ubuntu20.04 x86_64"

DISTRO_COMMENT="Ubuntu 20.04 Focal x86_64"

TARBALL_STRIP_OPT=0

# Download the x86_64 Ubuntu base
TARBALL_URL['x86_64']="https://cdimage.ubuntu.com/ubuntu-base/focal/daily/current/focal-base-amd64.tar.gz"

TARBALL_SHA256['x86_64']="16c831cc71b8ab79e5156451558df4a025783ba335047f6343518e7225416929"

Install qemu-user-x86-64

pkg install qemu-user-x86-64

Install Ubuntu

proot-distro install ubuntu20.04_x86_64

proot-distro login ubuntu20.04_x86_64

Through the uname -a command, you can see that the architecture is x86_64, and no Exec format error appears.
If a signal 11 Segmentfault error appears while installing packages, just run dpkg --configure -a once.

4. Compare native and emulated execution speed
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Note: qemu-user in the table below refers to the method in this article

native represents the arm64 executables installed in proot Ubuntu

Box64 means using the box64 command in proot Ubuntu to translate and run x86_64 executables

Use 7z to extract a 133MB zip file, and use time to measure how long it takes to complete.

QEMU User Mode on Ivon's Blog

Use debootstrap on x86 to create an ARM rootfs and install a chroot Debian environment on Android

Use Termux qemu-user to emulate x86_64 Ubuntu on ARM64 Android

1. Explanation #

2. Test environment #

3. Create an x86_64 proot Ubuntu #

4. Compare native and emulated execution speed #

1. Explanation
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2. Test environment
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3. Create an x86_64 proot Ubuntu
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4. Compare native and emulated execution speed
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