Setting up a Debian VM with QEMU, Expanding Storage, and Configuring `sbuild` for Packaging

In this post, I will document my experience setting up a Debian virtual machine using QEMU, expanding its storage properly, and configuring the sbuild tool to package Debian projects, including some of the errors I faced and how I solved them.

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Creating the Debian VM with QEMU

I started by creating a Debian VM using QEMU on Windows. I wrote a simple batch script (start_vm.bat) to launch the VM with 2GB of RAM and SSH port forwarding from host port 2222 to guest port 22:

@echo off
REM Script to start Debian VM in QEMU with 2GB RAM and SSH redirection

qemu-system-x86_64 ^
 -m 2048 ^
 -drive file="C:\VMs\debian\debian.qcow2",format=qcow2 ^
 -netdev user,id=net0,hostfwd=tcp::2222-:22 ^
 -device virtio-net-pci,netdev=net0 ^
 -nographic

pause

This allowed me to easily start the VM and connect via SSH on port 2222 of my host machine.

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Expanding VM Storage Properly

After some usage, I ran out of disk space inside the VM while building projects. Instead of increasing RAM, I decided to increase the disk image size.

I used this command on the host to expand the VM disk by 5GB:

qemu-img resize C:\VMs\debian\debian.qcow2 +5G

But expanding the disk image is only the first step. Inside the Debian VM, I had to expand the existing partition and filesystem to use this additional space.

Initially, I tried to delete and recreate the partition using tools like fdisk or parted to allocate the new space, but this approach didn’t work well for me. It risked breaking the VM or losing data, and involved unmounting partitions or booting from a live CD, which I wanted to avoid.

Instead, I followed a safer and simpler process without needing a live environment:

1. Installed the cloud-guest-utils package (which provides the growpart tool):

sudo apt update
sudo apt install cloud-guest-utils

1. Expanded the partition with growpart:

sudo growpart /dev/sda 1

1. Expanded the ext4 filesystem online:

sudo resize2fs /dev/sda1

After this, running df -h confirmed the root filesystem size increased from ~2.9GB to ~7.7GB, giving me plenty of extra space.

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Setting up sbuild for Debian Packaging

I then set up sbuild to build Debian packages for my Ruby project using Rack.

The official Debian Brasil documentation helped a lot, but I encountered some errors:

1. Directory Not Empty

When running:

sudo sbuild-debian-developer-setup

I got:

/srv/chroot/unstable-amd64-sbuild is not empty

Fix: Removed the directory carefully (making sure I was not inside it):

sudo rm -rf /srv/chroot/unstable-amd64-sbuild

2. Mirror Not Accessible (APT Proxy Issue)

The setup script tried using a local APT proxy (http://localhost:3142) which I wasn’t running, causing:

Failed getting release file ...

Fix: Created the chroot manually with a valid mirror:

sudo sbuild-createchroot unstable /srv/chroot/unstable-amd64-sbuild http://deb.debian.org/debian

This worked perfectly.

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Final Thoughts

• Always exit directories before deleting them.
• Verify your APT mirrors and proxies to avoid download errors.
• Use sbuild-createchroot for more control if needed.

After the setup, building packages worked smoothly with:

sbuild package