Ubuntu rootfs customization

The following is based on Ubuntu 18.04 64bit rootfs customization as
an example.

Preparatory work

Install qemu

Install emulator on Linux PC host:

   sudo apt-get install qemu-user-static

Download and extract ubuntu-core

Users can go to

ubuntu cdimg

 to download, choose to download "ubuntu-base-18.04.5-base-
arm64.tar.gz".

After downloading, create a temporary folder and unzip the root file
system:

   mkdir temp
   sudo tar -xpf ubuntu-base-18.04.5-base-arm64.tar.gz -C temp

Modify the root file system

Preparatory

Preparatory network:

   sudo cp -b /etc/resolv.conf temp/etc/resolv.conf

Preparatory qemu:

   sudo cp /usr/bin/qemu-aarch64-static temp/usr/bin/

Create a file mount.sh  mount.sh content:

   #!/bin/bash
   mnt() {
   	echo "MOUNTING"
   	sudo mount -t proc /proc ${2}proc
   	sudo mount -t sysfs /sys ${2}sys
   	sudo mount -o bind /dev ${2}dev
   	sudo mount -o bind /dev/pts ${2}dev/pts
   }
   umnt() {
   	echo "UNMOUNTING"
   	sudo umount ${2}proc
   	sudo umount ${2}sys
   	sudo umount ${2}dev/pts
   	sudo umount ${2}dev
   }

   if [ "$1" == "-m" ] && [ -n "$2" ] ;
   then
   	mnt $1 $2
   elif [ "$1" == "-u" ] && [ -n "$2" ];
   then
   	umnt $1 $2
   fi

Run mount.sh

Note: Remember to umount after customization !!!

   chmod +x mount.sh
   ./mount.sh -m temp/

Enter the root file system for operation:

   sudo chroot temp

Update and installation

Update:

   apt update
   apt upgrade

At least install systemd

   apt install -y systemd

Install the functionality you need:

   apt install vim git ....(Add as needed)

Install xubuntu

   apt install xubuntu-desktop

Errors may occur:

   E: Unable to locate package xxxx

Installation package source is not added to the

/etc/apt/source.list

, lead to can't identify the installation package, can add source by
oneself, also can use the following given

source.list

 covered the original

/etc/apt/source.list

 file:

   # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
   # newer versions of the distribution.

   deb http://ports.ubuntu.com/ubuntu-ports/ bionic main restricted
   deb-src http://ports.ubuntu.com/ubuntu-ports/ bionic main restricted

   ## Major bug fix updates produced after the final release of the
   ## distribution.
   deb http://ports.ubuntu.com/ubuntu-ports/ bionic-updates main restricted
   deb-src http://ports.ubuntu.com/ubuntu-ports/ bionic-updates main restricted

   ## Uncomment the following two lines to add software from the 'universe'
   ## repository.
   ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
   ## team. Also, please note that software in universe WILL NOT receive any
   ## review or updates from the Ubuntu security team.
   deb http://ports.ubuntu.com/ubuntu-ports/ bionic universe
   deb-src http://ports.ubuntu.com/ubuntu-ports/ bionic universe
   deb http://ports.ubuntu.com/ubuntu-ports/ bionic-updates universe
   deb-src http://ports.ubuntu.com/ubuntu-ports/ bionic-updates universe

   ## N.B. software from this repository may not have been tested as
   ## extensively as that contained in the main release, although it includes
   ## newer versions of some applications which may provide useful features.
   ## Also, please note that software in backports WILL NOT receive any review
   ## or updates from the Ubuntu security team.
   deb http://ports.ubuntu.com/ubuntu-ports/ bionic-backports main restricted
   deb-src http://ports.ubuntu.com/ubuntu-ports/ bionic-backports main restricted

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

Add user and set password

Add user:

   useradd -s '/bin/bash' -m -G adm,sudo firefly

Set the password for user:

   passwd firefly

Set the password for root:

   passwd root

Modify your root file system can exit:

   exit

Must umount

   ./mount.sh -u temp/

Make the root file system

Make your own root file system, depending on the size of your root
file system, and note that the "count" value is modified based on the
size of the "temp" folder:

   dd if=/dev/zero of=linuxroot.img bs=1M count=2048
   sudo mkfs.ext4 linuxroot.img
   mkdir  rootfs
   sudo mount linuxroot.img rootfs/
   sudo cp -rfp temp/*  rootfs/
   sudo umount rootfs/
   e2fsck -p -f linuxroot.img
   resize2fs  -M linuxroot.img

"linuxroot.img" is the final root file system image file.

FAQs

Q: After the root file system is loaded, the size is not normal and
does not occupy the entire partition?

A:

 Execute the extended file system command after the system is loaded
correctly:

    resize2fs /dev/mtd/by-name/linuxroot