Custom initramfs generator on Gentoo

initramfs.sh

#!/usr/bin/env bash
echo "Generating initramfs source structure"
cd /usr/src/initramfs && rm -r *
mkdir -p {bin,dev/mapper,etc,lib,lib64,mnt/root,proc,root,sbin,sys,run}
cp --archive /dev/{null,console,tty} dev

# Required executables
cp \
	/bin/busybox \
	bin/

cp \
	/sbin/cryptsetup \
	sbin/

# Required dynamically link libraries
cp \
	/lib64/ld-linux-x86-64.so.2 /lib64/libpam.so.0* /lib64/libpam_misc.so.0* /lib64/libc.so.6 \
	/lib64/libuuid.so.1 \
	/lib64/libblkid.so.1 \
	/lib64/libdevmapper.so.1.02 \
	/lib64/libudev.so.1 \
	/lib64/libm.so.6 \
	lib64/
cp \
	/usr/lib64/libcryptsetup.so.12 \
	/usr/lib64/libpopt.so.0 \
	/usr/lib64/libssl.so.1.1 \
	/usr/lib64/libcrypto.so.1.1 \
	/usr/lib64/libargon2.so.1 \
	/usr/lib64/libjson-c.so.5 \
	lib64/
# Required implicitly
cp \
	/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/libgcc_s.so \
	/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/libgcc_s.so.1 \
	lib64/

echo "Generating init script"

# Write the init script
cat > init << EOF
#!/bin/busybox sh

rescue_shell() {
	echo "Something went wrong. Sadly there's nothing you can do."
	exec poweroff -f
	#exec /bin/sh
}

# Mount the /proc and /sys/ filesystems
mount -t devtmpfs none /dev
mount -t proc none /proc
mount -t sysfs none /sys
# Print only very important messages
sysctl -w kernel.printk="0 1 2"

# Mount the rootfs
echo "Mounting root ..."
/sbin/cryptsetup luksOpen --allow-discards $(findfs UUID="b06abd50-20b8-4705-af9b-7fb7fce3b42f") cryptoroot || rescue_shell
mount -t btrfs -o ro $(findfs UUID="0b836400-d4b4-43ca-859f-71f4fe20a0d1") /mnt/root || rescue_shell

# Mount other file systems (without prompt)
/sbin/cryptsetup luksOpen --key-file=/mnt/root/keyfile --allow-discards $(findfs UUID="4dd83704-ec34-4e42-a3cc-ca5d5fc0d74b") cryptoswap || rescue_shell
swapon -d $(findfs UUID="ab6a7da2-6643-472b-ad4f-1599f82cab14") || rescue_shell

# Cleanup
umount /dev /proc /sys

# Boot the real thing
exec switch_root /mnt/root /usr/lib/systemd/systemd || rescue_shell
EOF

chmod +x init

echo "Finished generating initramfs"

echo "Packing into zstd cpio-archive"
OUT=../initramfs.cpio.zstd
[ -f "$OUT" ] && rm "$OUT"
find . | cpio -o -H newc | zstd - --ultra -o $OUT