Raspberry Pi ZeroなどをUSB接続したマシンからmicroSDなしでOS起動

#! /bin/sh

if test $# -ne 2; then
    printf "USAGE: %s [RASPBIAN IMAGE] [DEST]\\n" "$0" >&2
    exit 1
fi

img="$1"
chrootdir="$2"

if ! mkdir -p "$chrootdir"; then
    echo "mkdir -p $chrootdir failed." >&2
    exit 1
fi

if ! loopdev=$(losetup -f -P --show "$img"); then
    echo "losetup -f -P --show $img failed." >&2
    exit 1
fi

if ! mount "${loopdev}"p2 -o ro /mnt; then
    echo "mount ${loopdev}p2 -o ro /mnt failed." >&2
    losetup -d "$loopdev"
    exit 1
fi

if ! cp -a /mnt/* "$chrootdir/"; then
    echo "cp -a /mnt/* $chrootdir/ failed." >&2
    umount /mnt
    losetup -d "$loopdev"
    exit 1
fi

umount /mnt

if ! mount "${loopdev}"p1 -o ro /mnt; then
    echo "mount ${loopdev}p1 -o ro /mnt failed." >&2
    losetup -d "$loopdev"
    exit 1
fi

if ! cp -a /mnt/* "$chrootdir/boot/"; then
    echo "cp -a /mnt/* $chrootdir/boot/ failed." >&2
    umount /mnt
    losetup -d "$loopdev"
    exit 1
fi

umount /mnt
losetup -d "$loopdev"
echo "Done."

#! /bin/sh
CHROOT_DIR=/path/to/raspbian/rootfs
for D in dev proc sys dev/shm dev/pts; do mount -o bind /${D} ${CHROOT_DIR}/${D}; done
mv ${CHROOT_DIR}/etc/ld.so.preload ${CHROOT_DIR}/etc/ld.so.preload.orig
chroot ${CHROOT_DIR} /bin/bash
mv ${CHROOT_DIR}/etc/ld.so.preload.orig ${CHROOT_DIR}/etc/ld.so.preload
for D in dev/pts dev/shm dev proc sys; do umount ${CHROOT_DIR}/${D}; done

(手動でupdate-initramfsを実行する場合)
QEMU# update-initramfs -k "X.Y.Z+" -c
QEMU# mv "/boot/initrd.img-X.Y.Z+" /boot/initrd.img

(無線LANをinitrdで使うためのスクリプトに実行属性を付けた後で/boot/initrd.imgとしてinitrdを書き出す)
QEMU# /path/to/final_commands.sh

(400MiBのext4ファイルシステムのファイルを作成する例)
$ dd if=/dev/zero of=raspbian.ext4 bs=1M count=400
$ mkfs.ext4 -m 0 -T small raspbian.ext4

(ファイルシステムをマウントしてローカルディスク上のRaspberry Pi OSのディレクトリの中身をこの中にコピーする)
$ sudo mount -t ext4 -o loop raspbian.ext4 /mnt
$ sudo cp -a /path/to/raspbian/{bin,etc,dev,home,lib,lost+found,media,mnt,opt,proc,root,run,sbin,srv,sys,tmp,usr,var} /mnt/
$ sudo umount /mnt

(/pizeroというディレクトリにマウントする場合の例・mkdirは一度行えばその後は不要)
NFSサーバマシン$ sudo mkdir /pizero
NFSサーバマシン$ sudo mount -t ext4 -o loop /path/to/raspbian.ext4 /pizero

/pizero 192.168.11.222(rw,sync,no_subtree_check,no_root_squash)

(NFS設定変更の反映・Debian系の場合)
NFSサーバマシン$ sudo systemctl restart nfs-server; sudo exportfs -a

dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/nfs nfsroot=192.168.11.1:/pizero rw ip=192.168.11.222:192.168.11.1::255.255.255.0:zerowh:wlan0:off elevator=deadline fsck.repair=yes modules-load=dwc2,g_ether rootwait g_ether.host_addr=11:22:33:44:55:66

# Zeroを周辺機器としてUSBケーブルでイーサネット通信するために必要
dtoverlay=dwc2,dr_mode=peripheral

# initrd.imgというファイル名のinitrdを読み込む
initramfs initrd.img followkernel

(実行例と出力例)
$ /path/to/rpiboot -d /path/to/boot
Waiting for BCM2835/6/7
Sending bootcode.bin
Successful read 4 bytes
Waiting for BCM2835/6/7
Second stage boot server
File read: config.txt
File read: start.elf
...
File read: overlays/dwc2.dtbo
File read: overlays/justboom-dac.dtbo
Second stage boot server done

(lsusbでの見え方の例)
PC$ lsusb
...
Bus 001 Device 006: ID 0525:a4a2 Netchip Technology, Inc. Linux-USB Ethernet/RNDIS Gadget
...

PC$ lsusb -t
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/10p, 480M
    ...
    |__ Port 7: Dev 6, If 0, Class=Communications, Driver=cdc_ether, 480M
    ...

QEMU# find /lib/modules/[バージョン]/ -name "*.ko" | while read line; do echo $(basename ${line%.ko}); done > modules

(Jessieの場合)
QEMU# apt install dropbear

(Busterの場合)
QEMU# apt install dropbear dropbear-initramfs

(Jessieの場合)
QEMU# mkdir -m 700 -p /etc/initramfs-tools/root/.ssh
QEMU# dropbearkey -t rsa -s 4096 -f /etc/initramfs-tools/root/.ssh/id_rsa.dropbear | grep ^ssh-rsa | tee /etc/initramfs-tools/root/.ssh/id_rsa.pub > /etc/initramfs-tools/root/.ssh/authorized_keys
QEMU# /usr/lib/dropbear/dropbearconvert dropbear openssh /etc/initramfs-tools/root/.ssh/id_rsa.dropbear /etc/initramfs-tools/root/.ssh/id_rsa
QEMU# chmod 600 /etc/initramfs-tools/root/.ssh/*

(Busterの場合)
QEMU# dropbearkey -t rsa -s 4096 -f /etc/dropbear-initramfs/id_rsa.dropbear | grep ^ssh-rsa > /etc/dropbear-initramfs/id_rsa.pub
QEMU# /usr/lib/dropbear/dropbearconvert dropbear openssh /etc/dropbear-initramfs/id_rsa.dropbear /etc/dropbear-initramfs/id_rsa

QEMU# cp -a /usr/share/initramfs-tools/scripts/local /etc/initramfs-tools/scripts/

mountroot()
{
	while true; do
		sh
	done
}

#!/bin/sh

PREREQ=""

prereqs()
{
	echo "$PREREQ"
}

case $1 in
prereqs)
	prereqs
	exit 0
	;;
esac

. /usr/share/initramfs-tools/hook-functions

copy_exec /bin/nano
copy_exec /lib/terminfo/s/screen
copy_exec /opt/vc/bin/vcgencmd
copy_exec /usr/share/alsa/alsa.conf

mountroot()
{
	mkdir -p /dev/shm
	mount -t tmpfs -o size=192M,rw,nosuid,nodev none /dev/shm
	while true; do
		sh
	done
}