Chroot into Raspberry Pi ARMv7 Image with Qemu

raspberry-pi-chroot-armv7-qemu.md

# install dependecies
apt-get install qemu qemu-user-static binfmt-support

# download raspbian image
wget https://downloads.raspberrypi.org/raspbian_latest

# extract raspbian image
unzip raspbian_latest

# extend raspbian image by 1gb
dd if=/dev/zero bs=1M count=1024 >> 2016-05-27-raspbian-jessie.img

# set up image as loop device
losetup /dev/loop0 2016-05-27-raspbian-jessie.img

# check file system
e2fsck -f /dev/loop0p2

#expand partition
resize2fs /dev/loop0p2

# mount partition
mount -o rw /dev/loop0p2  /mnt
mount -o rw /dev/loop0p1 /mnt/boot

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

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

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

# chroot to raspbian
chroot /mnt /bin/bash
	# do stuff...
	exit

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

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

# unmount loop device
losetup -d /dev/loop0

---

Source

dd if=/dev/zero bs=1M count=1024 >> 2016-05-27-raspbian-jessie.img

This step increased the .img file's size (and thus the device's size), but resize2fs /dev/loop0p2 would not grow the partition:

resize2fs 1.42.13 (17-May-2015)
The filesystem is already 858112 (4k) blocks long.  Nothing to do!

even though cfdisk reported 1G free space after the p2 partition. So i noted the partition type (your typical linux), since it was the last partition and after it was the desired free space to the end of the "disk", i deleted the partition and recreated it with all available space.

Then resize2fs successfully expanded the ex4 filesystem in the partition to match the full size.

As noted above, I used this script with a physical SDCard, so I skipped that step. Looking at it, I think there's no step included to resize the partition. resize2fs resizes the ext4 filesystem to the size of the partition, but the partition is not enlarged first AFAIK. The image is expanded, but that data is not automatically part of the last partition. In fact if the disk uses GPT (which is likely nowadays), you need software that will not only resize the partition, but also modify the GPT headers and move their copies which are written at the end of the medium. I think software like parted and gdisk can do this.

parted was just the hint I needed. For anyone that wants to resize their image properly, this is how I did it:

First, list the partitions:

$ sudo parted 2016-05-27-raspbian-jessie.img print

Model:  (file)
Disk /home/pop_desktop/workspace/raspiblitz_ci/2021-03-04-raspios-buster-arm64.img: 3729MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start   End     Size    Type     File system  Flags
 1      4194kB  273MB   268MB   primary  fat32        lba
 2      273MB   3729MB  3456MB  primary  ext4

Use this to determine the partition number you want, and the "end" of the partition. I wanted partition 2, as that's the home partition that needs to grow.

Then grow the partition like so:

loop=$(losetup -f)  # Find the first available loop device

# extend raspbian image by 1gb
dd if=/dev/zero bs=1M count=1024 >> raspios.img
sudo parted raspios.img resizepart 2 4700MB

# set up image as loop device
losetup -P $loop raspios.img

# check file system
e2fsck -y -f ${loop}p2

#expand partition
resize2fs ${loop}p2

In the above example, I changed the "end" of the ext4 partition to 4700MB, roughly increasing it by 1GB.