RootFS Builder

A simple RootFS builder for many distros

manjaro based root-fs tar.gz creation

• install instruction set's dependant packages : aria2(1.25.0>=) fastboot adb
• you can find manjaro arm downloads at this link. choose the edition you prefer. in this quide , I will be using kde-plasma with version 20.02 found at this link.

[WARN] do not choose emmc installer , choose the other image. e.g. Manjaro-ARM-kde-plasma-pbpro-20.02.img.xz

the following snippet uses aria2 to quickly download it and save it as manjaro.img.xz under /tmp directory

export manjaro_out_name="manjaro"; \
export manjaro_dir="/tmp"; \
export manjaro_url="https://osdn.net/projects/manjaro-arm/storage/pbpro/kde-plasma/20.02/Manjaro-ARM-kde-plasma-pbpro-20.02.img.xz"; \
aria2c -c \
       -j16 \
       -x16 \
       -k 1M \
       --out="${manjaro_out_name}.img.xz" \
       --dir="$manjaro_dir" \
       "$manjaro_url"; \
unset manjaro_url;

• extract the downloaded image

unxz "${manjaro_dir}/${manjaro_out_name}.img.xz"

• we need to calculate offeset to mount the image. use fdisk -l to probe images information. you would need sector size and boot start values. starting offset for mount is equal to (boot start) x (sector size)

• you can use the following snippet to get sector size

fdisk -l "${manjaro_dir}/${manjaro_out_name}.img" | grep -Po '(?<= \= )[^ bytes]+'

• you can use the following snippet to get boot start

fdisk -l "${manjaro_dir}/${manjaro_out_name}.img" | grep -v 'sectors' | grep "${manjaro_dir}/${manjaro_out_name}" |  tr -s ' ' | cut -d ' ' -f2

• mount the image based on calculated offset

export offset="32000000"; \
sudo mkdir -p "/mnt/${manjaro_out_name}"; \
sudo mount -o loop,offset="${offset}" "${manjaro_dir}/${manjaro_out_name}.img" "/mnt/${manjaro_out_name}";
unset offset;

• change directory and archive whatever was inside the mounted directory

[WARN] make sure symlinks are preserved after archiving

pushd "/mnt/${manjaro_out_name}"; \
sudo tar -zcvf "/tmp/${manjaro_out_name}.tar.gz" . ; \
popd; \
sudo umount /mnt/${manjaro_out_name}; \
sudo rm -rf /mnt/${manjaro_out_name}; \
rm "/tmp/${manjaro_out_name}.img"; \
sudo chown "$UID" "/tmp/${manjaro_out_name}.tar.gz";

setting up your distro on the device

• Enable USB debugging and OEM Unlock on your pixel c device.
• exit pixel-c container if your shell is still in it. you can use the following snippet
• download twrp recovery from this link.
• boot twrp recovery by running the following snippet

fastboot boot twrp.img

• wipe you /data/ partition. in twrp recovery, there is a wipe option. go there and factory reset device
• mount /data/ and /cache/ in twrp
• download busybox static build for armv8 just in case busybox in twrp has any issue. as an example , the following snippet downloads busybox 1.31.0

export busybox_version=1.31.0; \
export busybox_url="https://busybox.net/downloads/binaries/${busybox_version}-defconfig-multiarch-musl/busybox-armv8l"; \
aria2c -c \
       -j16 \
       -x16 \
       -k 1M \
       --out="busybox" \
       --dir="$manjaro_dir" \
       "$busybox_url"; \
unset busybox_url;unset busybox_version

• move busybox to /cache/ and generated rootfs to /data/ your device and then use adb shell to get a shell into your pixel c . you can use the following snippet

export rootfs="arch_rootfs.tar.gz"; \
adb push "/tmp/${manjaro_out_name}.tar.gz" /data/ && \
adb push /tmp/busybox /cache/ && \
adb shell

• run the follwing in adb shell ( on your device ) to extract rootfs

rootfs="arch_rootfs.tar.gz"; \
chmod +x /cache/busybox && \
cd /data && \
/cache/busybox tar xvf "$rootfs" && \
rm "$rootfs" && \
exit; \
unset rootfs;

• reboot to bootloader to flash boot image

adb reboot bootloader

• flash a signed boot image with fastboot. you can use the following snippet

export boot_image=boot.img; \
fastboot flash boot "$boot_image" ; \
unset  boot_image;

• clean up env vars

unset manjaro_out_name;unset manjaro_dir;