auto_decompress_kernel for ubuntu20.04 server / rpi usb boot (improved)

auto_decompress_kernel

#!/bin/bash -e

# Put this script in the root of the boot partition (i.e. system-boot) and chmod it with +x
# Set Variables
BTPATH=/boot/firmware
CKPATH=$BTPATH/vmlinuz
DKPATH=$BTPATH/vmlinux

#Check if compression needs to be done.
if [ -e $BTPATH/check.md5 ]; then
	if md5sum --status --ignore-missing -c $BTPATH/check.md5; then
	echo -e "\e[32mFiles have not changed, Decompression not needed\e[0m"
	exit 0
	else echo -e "\e[31mHash failed, kernel will be compressed\e[0m"
	fi
fi

#Backup the old decompressed kernel
mv -f $DKPATH $DKPATH.bak

if [ ! $? == 0 ]; then
	echo -e "\e[31mDECOMPRESSED KERNEL BACKUP FAILED!\e[0m"
	exit 1
else 	echo -e "\e[32mDecompressed kernel backup was successful\e[0m"
fi

#Decompress the new kernel
echo "Decompressing kernel: "$CKPATH".............."

zcat $CKPATH > $DKPATH

if [ ! $? == 0 ]; then
	echo -e "\e[31mKERNEL FAILED TO DECOMPRESS!\e[0m"
	exit 1
else
	echo -e "\e[32mKernel Decompressed Succesfully\e[0m"
fi

#Hash the new kernel for checking
md5sum $CKPATH $DKPATH > $BTPATH/check.md5

if [ ! $? == 0 ]; then
	echo -e "\e[31mMD5 GENERATION FAILED!\e[0m"
	else echo -e "\e[32mMD5 generated Succesfully\e[0m"
fi

#Exit
exit 0

install_999_decompress_rpi_kernel

#!/bin/bash -e

sudo echo 'DPkg::Post-Invoke {"/bin/bash /boot/firmware/auto_decompress_kernel"; };' > /etc/apt/apt.conf.d/999_decompress_rpi_kernel
sudo chmod +x /etc/apt/apt.conf.d/999_decompress_rpi_kernel

The file above should be placed in /etc/apt/apt.conf.d/999_decompress_rpi_kernel

Instructions.

1. Before booting, add the auto compress kernel script to the system-boot partition

2. On first boot, as root, install the auto compress kernel script:

curl https://gist.githubusercontent.com/24HOURSMEDIA/96c472f3301f594b38d78755bef2124e/raw/709eec71bfe69120ec472d92659e81eea420f939/install_999_decompress_rpi_kernel | bash