Chroot to pi sd card

chroot-to-pi.sh

#!/bin/bash

# This script allows you to chroot ("work on") 
# the raspbian sd card as if it's the raspberry pi
# on your Ubuntu desktop/laptop
# just much faster and more convenient

# credits: https://gist.github.com/jkullick/9b02c2061fbdf4a6c4e8a78f1312a689

# make sure you have issued
# (sudo) apt install qemu qemu-user-static binfmt-support

# Write the raspbian image onto the sd card,
# boot the pi with the card once 
# so it expands the fs automatically
# then plug back to your laptop/desktop
# and chroot to it with this script.

# Invoke:
# (sudo) ./chroot-to-pi.sh /dev/sdb 
# assuming /dev/sdb is your sd-card
# if you don't know, when you plug the card in, type:
# dmesg | tail -n30 


# Note: If you have an image file instead of the sd card, 
# you will need to issue 
# (sudo) apt install kpartx
# (sudo) kpartx -v -a 2017-11-29-raspbian-stretch-lite.img
# then
# (sudo) ./chroot-to-pi.sh /dev/mapper/loop0p
# With the vanilla image, you have very little space to work on
# I have not figured out a reliable way to resize it
# Something like this should work, but it didn't in my experience
# https://gist.github.com/htruong/0271d84ae81ee1d301293d126a5ad716
# so it's better just to let the pi resize the partitions

mkdir -p /mnt/raspbian

# mount partition
mount -o rw ${1}2  /mnt/raspbian
mount -o rw ${1}1 /mnt/raspbian/boot

# mount binds
mount --bind /dev /mnt/raspbian/dev/
mount --bind /sys /mnt/raspbian/sys/
mount --bind /proc /mnt/raspbian/proc/
mount --bind /dev/pts /mnt/raspbian/dev/pts

# ld.so.preload fix
sed -i 's/^/#CHROOT /g' /mnt/raspbian/etc/ld.so.preload

# copy qemu binary
cp /usr/bin/qemu-arm-static /mnt/raspbian/usr/bin/

echo "You will be transferred to the bash shell now."
echo "Issue 'exit' when you are done."
echo "Issue 'su pi' if you need to work as the user pi."

# chroot to raspbian
chroot /mnt/raspbian /bin/bash

# ----------------------------
# Clean up
# revert ld.so.preload fix
sed -i 's/^#CHROOT //g' /mnt/raspbian/etc/ld.so.preload

# unmount everything
umount /mnt/raspbian/{dev/pts,dev,sys,proc,boot,}

I would add something like to establish internet connection:

# establish internet connection
mv /mnt/raspbian/etc/resolv.conf /mnt/raspbian/etc/resolv.conf_bak
cp /etc/resolv.conf /mnt/raspbian/etc/

And in the cleanup section:

# revert /etc/resolv.conf_bak
rm /mnt/raspbian/etc/resolv.conf 
mv /mnt/raspbian/etc/resolv.conf_bak /mnt/raspbian/etc/resolv.conf

Just saw that somebody above already suggested adding resolv.conf as a mount bind. I will test if this is the better way.

sudo ./pi-chroot /dev/sdc

You will be transferred to the bash shell now.
Issue 'exit' when you are done.
Issue 'su pi' if you need to work as the user pi.
chroot: failed to run command ‘/bin/bash’: Exec format error

i have a feeling i got this error since im running it on arch linux and binfmt-support is not avaible in arch

@SX-9 Are you sure you got qemu working? There are some checks you can use here to see some more about what isn't setup properly.

If anyone on arch is trying this, you can basically just install qemu-user-static-binfmt and just run sudo arch-chroot . on the rootfs (optionally mounting boot first).

For those using Gentoo, make sure you've built qemu package with static-user and QEMU_SOFTMMU_TARGETS: arm QEMU_USER_TARGETS: arm. Further info in the official handbook: https://wiki.gentoo.org/wiki/Embedded_Handbook/General/Compiling_with_QEMU_user_chroot

Alternative to dmesg | tail -n30

• lsblk -o NAME,MOUNTPOINT
• check the mount in /media/<user_name>/

You rock! Just tested the script in a Rasp Pi 4 and it worked like magic!

Alternative to dmesg | tail -n30

• lsblk -o NAME,MOUNTPOINT
• check the mount in /media/<user_name>/

I learned this neat trick, if you do dmesg -w and then plug the drive in, you'll be able to watch the dmesg in real-time!

Or, just use systemd-nspawn (systemd-container package in apt repos)

If an img file, loop and mount root and boot, then:

sudo systemd-nspawn -D /mnt bin/bash

Pretty straight forward description here: https://wiki.debian.org/RaspberryPi/qemu-user-static (Option 2.2)

Edit:
If you need internet access you might want to include the option --resolv-conf=replace-stub or --resolv-conf=copy-host depending on how your host is setup. If you have systemd-resolved on host, try replace-stub first.

In script for example (assuming you run it as root, this will drop you into the container):

#!/usr/bin/env bash

# do loop stuff and then mount root and boot

if systemctl is-active -q systemctl-resolved.service; then
  systemd-nspawn --resolv-conf=replace-stub -D /mnt bin/bash
else
  systemd-nspawn --resolv-conf=copy-host -D /mnt bin/bash
fi

exit 0

Edit
If you only want to execute stuff from a script, you can either change bin/bash to the command you want to execute, or use --pipe and then exit the container (change --resolv-conf to the method you need):

systemd-nspawn --pipe --resolv-conf=copy-host -D /mnt bin/bash << EOF
apt update
apt upgrade
exit
EOF

shamless self promotion incoming
This will be implemented in next version of shrink-backup btw...