Modify rootfs root file system image content

1. Create a new mount directory rootfs

mkdir rootfs

2. Mount rootfs.img to the created directory.
   Before mounting, make a backup of the root file system image to prevent damage to the root file system that cannot be restored due to modification errors.

cp ubuntu.img ubuntu.img-bak

Mount the root filesystem image

sudo mount ubuntu.img rootfs/

ls rootfs/Check if the mount is successful

3. Mount rootfs/it to the host
   using the mount script mnt.shto mount
   Reference link: Ubuntu root file system custom
   mnt.sh source code

#!/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
	# sudo mount /dev/sda1 ${2}
	sudo chroot ${2}
}
umnt() {
	echo "UNMOUNTING"
	sudo umount ${2}proc
	sudo umount ${2}sys
	# sudo umount ${2}dev/sda1 
	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
else
	echo ""
	echo "Either 1'st, 2'nd or both parameters were missing"
	echo ""
	echo "1'st parameter can be one of these: -m(mount) OR -u(umount)"
	echo "2'nd parameter is the full path of rootfs directory(with trailing '/')"
	echo ""
	echo "For example: ch-mount -m /media/sdcard/"
	echo ""
	echo 1st parameter : ${1}
	echo 2nd parameter : ${2}
fi

Mount command:

sudo ./mnt.sh -m rootfs/

After the target file is mounted, it needs to be /
added. After the mount is successful, the terminal user will display asroot

4. Modify the root file system image
   At this point, you can modify the root file system in the operating environment of the host machine, and you can directly use the download command to install the commands required by the root file system, and the downloaded command will be directly installed in the root file system
5. Exit the root file system mirror mount

exit

6. Uninstall the root file system image from the host
   Uninstall command:

sudo ./mnt.sh -u rootfs/

7. Unmount the root file system mirror mount point

sudo umount rootfs

After successfully unmounting the root file system image, the changes have been saved to the root file system image

Summary: This article mainly uses the chroot command to mount the root file system to the host for modification