Deboostraping Debian Stretch arm64 rootfs for Raspberry Pi 3

Debootstrap the Rootfs

To create our bare filesystem, we need:

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//make sure these are installed:
debootstrap
binfmt-support

TO build the 1st stage of Debian rootfs:

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mkdir debianFS
sudo debootstrap --arch=arm64 --foreign stretch debianFS

Once the 1st sstage is done… onto next step below.

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// To chroot onto the rootfs
sudo cp -av /usr/bin/qemu-aarch64-static $HOME/debianFS/usr/bin

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// To have internet access temporarily borrowing from host
// If your host is Ubuntu 17.10
sudo cp -av /run/systemd/resolve/stub-resolv.conf $HOME/debianFS/etc/resolv.conf

// For Ubuntu 16.04.3 below
sudo cp -av /run/resolvconf/resolv.conf $HOME/debianFS/etc/resolv.conf

Modifying the Rootfs

Going back from when we compile the Raspberry Pi 3 kernel, We are goig to install the kernel module and firmware into the debianFS folder that we just created above.

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sudo make -C rpi-4.14.70/ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=$HOME/bo_4.14/ modules_install INSTALL_MOD_PATH=$HOME/debianFS/

Verify that it was installed correctly. And remove build and source links.

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ls $HOME/debianFS/lib/modules/4.11~

modules.builtin     modules.devname        modules.symbols.bin  build
kernel              modules.builtin.bin    modules.order        source
modules.alias       modules.dep            modules.softdep
modules.alias.bin   modules.dep.bin        modules.symbols

sudo find $HOME/debianFS/ -name build | xargs rm -rf
sudo find $HOME/debianFS/ -name source | xargs rm -rf

Then chroot to further setup our filesystem.

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sudo chroot debianFS

Now that you’re in the chroot environment, we are ready to setup the 2nd stage of debootstrap.

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export LANG=C

/debootstrap/debootstrap --second-stage

After the installation has finished, add a debian repository

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nano /etc/apt/sources.list

// replace it with these below:

deb http://deb.debian.org/debian stretch main

Fetch the latest package lists from server then upgrade.

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apt-get update
apt-get upgrade

Install minimal packages:

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apt-get install sudo ifupdown net-tools ethtool udev wireless-tools iputils-ping resolvconf wget apt-utils wpasupplicant

And we can now add an admin user with sudo permission.

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useradd -G sudo -m -s /bin/bash pi3
echo pi3:pi3 | chpasswd

The format input line of chpasswd is: user_name:password.

Change root password with these command:

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passwd root

You can setup your hostname here for your target device or in the kernel configuration making sure that the hostname is empty.

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echo U-Base_min > /etc/hostname
echo 127.0.0.1	localhost > /etc/hosts
echo 127.0.1.1	U-Base_min >> /etc/hosts

Then install these first:

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apt-get install dialog perl

We need those installed first to correct some error messages about locale: If locale-gen command is missing, apt-get install locales first.

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locale-gen "en_US.UTF-8"
        Generating locales...
            en_US.UTF-8... done
        Generation complete.

To-Do: gonna use Netplan for future network management

We need to add /etc/fstab file entry below coz’ if not…it will run on read-only mode. Below are Tab not spacebar

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nano /etc/fstab

// add these line below or your fs will be on read-only

/dev/mmcblk0p2	/	ext4	defaults,noatime	0	1

When everything you want are done, exit chroot:

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exit

Removing unwanted files

To reduce the rootfs/ size we can remove some unwanted files. Create a file /etc/dpkg/dpkg.cfg.d/01_nodoc which specifies the desired filters. Example:

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path-exclude /usr/share/doc/*
# we need to keep copyright files for legal reasons
path-include /usr/share/doc/*/copyright
path-exclude /usr/share/man/*
path-exclude /usr/share/groff/*
path-exclude /usr/share/info/*
# lintian stuff is small, but really unnecessary
path-exclude /usr/share/lintian/*
path-exclude /usr/share/linda/*

Then you can manually remove any documentation already installed:

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sudo find rootfs/usr/share/doc -depth -type f ! -name copyright|xargs rm || true
sudo find rootfs/usr/share/doc -empty|xargs rmdir || true
sudo rm -rf rootfs/usr/share/man/* rootfs/usr/share/groff/* rootfs/usr/share/info/*
sudo rm -rf rootfs/usr/share/lintian/* rootfs/usr/share/linda/* rootfs/var/cache/man/*

Then copy the $HOME/debianFS/* content to the 2nd partition of your MicroSD card.

Creating the Image file (*Optional)

We could make an image file with several partition on it. We will create a 700M empty img file:

Modify the desired image size according to your needs. I use resize2fs after i boot this up

sudo dd if=/dev/zero of=myimage.img bs=700K count=1024

Then partition it using fdisk in my case:

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sudo fdisk -l myimage.img
        Result:
        | Device     w| Boot | Start 	| End	  | Sectors |
        |:-----------|:-----|:----------|:--------|:--------|
        | myimage1   |      | 2048  	| 264191  | 1024000 | Fat32
        | myimage2   |      | 264192 	| 1433599 | 3168256 | Linux

For 32Bit - kernel bootup message sometimes do not show up. But using a usb-serial with putty you’ll know the kernel boots up…

To assign a loopback device and be able to format it.

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sudo losetup -o $((512*2048)) --sizelimit $((512*264191)) /dev/loop14 myimage.img 
sudo losetup -o $((512*264192)) --sizelimit $((512*1433599)) /dev/loop15 myimage.img
sudo mkfs.vfat -F 32 -n 'SYS-BOOT' /dev/loop14
sudo mkfs.ext4 /dev/loop15

mkfs.vfat -n partition name /dev/loop1.

Mount and Copy those necessary files that we need to their respected partition. Install dosfstools if cannot mount vfat

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sudo mount /dev/loop14 /mnt/boot
sudo mount /dev/loop15 /mnt/rootfs

// run sync before umounting and after copying files are done
sync

    # Then umount and detach:
sudo umount /dev/loop14
sudo umount /dev/loop15
sudo losetup --detach /dev/loop14
sudo losetup --detach /dev/loop15

You can now burn that myimage.img to yor MicoSD card. Now boot it up and you should now be able to login.

Reference :

How to create bare minimum Debian Wheezy rootfs from scratch