debsb 0.2.3

Debian Sid Sandbox — instant QEMU/KVM VM from cloud images

debsb

Debian Sid sandbox in one command. Downloads a Debian cloud image, boots it in QEMU/KVM, and gives you an isolated VM with auto-login, SSH, and shared filesystem. No kernel building, no complex setup.

Motivation

I just want a fully hackable Debian setup—both user space and kernel—within a restricted sandbox.

I want to avoid rebuilding an OpenSSH-enabled rootfs for each fuzzing test and repeatedly using the -kernel and -initrd flags in QEMU.

Install

pip install debsb

Dependencies

• qemu-system-x86_64 (with KVM support)
• cloud-image-utils (cloud-localds)
• whois (mkpasswd)
• wget
• ssh

On Debian/Ubuntu:

sudo apt install qemu-system-x86 cloud-image-utils whois wget openssh-client

For upstream kernel builds (debsb build <path>), additionally:

sudo apt install build-essential flex bison bc libelf-dev libssl-dev libncurses-dev dwarves pahole libdw-dev libdwarf-dev kmod debhelper

For --debian kernel builds, additionally:

sudo apt install python3-dacite python3-debian python3-jinja2 debhelper quilt rsync devscripts dh-python

Usage

Build the sandbox (one-time)

debsb build --size 20G

This downloads the Debian Sid cloud image, configures SSH keys and auto-login, and runs first boot. All artifacts are stored in ~/.debsb/.

Use --reset to skip the prompt and rebuild from scratch:

debsb build --size 20G --reset

Build with a custom kernel (upstream)

debsb build ~/linux --configitem CONFIG_KASAN=y --configitem CONFIG_KCOV=y

This:

1. Sets up the cloud image (if not already done)
2. Generates a default kernel config (make defconfig) with VM-essential options
3. Applies --configitem entries
4. Runs make olddefconfig and make bindeb-pkg
5. Installs the resulting .deb into the VM via GRUB

Build with Debian kernel

This kernel image is built based on the official Debian repository.

• https://salsa.debian.org/kernel-team/linux

# Default branch (debian/latest)
debsb build --debian --configitem CONFIG_KASAN=y --configitem CONFIG_KCOV=y

# Specific branch
debsb build --debian --branch debian/sid

This clones the Debian kernel from salsa.debian.org/kernel-team/linux.git, applies config items to debian/config/config, and builds the amd64 kernel package using the Debian packaging rules. The resulting kernel is installed into the VM via GRUB.

Run the sandbox

# Serial console (auto-login as debian, Ctrl-A X to quit)
debsb run

# SSH session (as debian)
debsb run --ssh

# SSH as root
debsb run --ssh --root

# Run a command and auto-shutdown (requires --ssh)
debsb run --ssh --root --exec "apt update && apt upgrade -y"

# Graphical QEMU window
debsb run --graphics

# With sound
debsb run --sound

# Extra QEMU options
debsb run --qemu-opts='-m 8192'

Execute a command

--exec runs a command via SSH and shuts down automatically. Requires --ssh:

debsb run --ssh --exec "uname -a"
debsb run --ssh --root --exec "ls -ahl .debsb"
debsb run --ssh --exec "./my-script.sh"

This is useful for CI/automation. The exit code of the command is propagated.

Verbose mode

Show kernel boot messages:

debsb run --verbose

Shared filesystem

Your host ~/.debsb/ directory is mounted inside the VM at:

• /root/.debsb (symlink to /mnt/debsb)
• /home/debian/.debsb (symlink to /mnt/debsb)

This is automatic — no manual mounting needed.

How it works

1. Downloads debian-sid-generic-amd64-daily.qcow2 from cloud.debian.org
2. Creates a cloud-init ISO with SSH keys, user config, and auto-login
3. Boots the VM with QEMU/KVM and waits for cloud-init to finish
4. On subsequent debsb run, boots the prepared image directly

When building with a kernel (debsb build <path> or debsb build --debian):

• The kernel .deb is installed into the VM
• GRUB is updated to boot the new kernel by default
• No -kernel or -initrd flags needed — GRUB handles boot

Accounts

User	Access
debian	Serial auto-login, SSH with key, sudo NOPASSWD
root	SSH with key (--root flag)

SSH key: ~/.debsb/id_ed25519 (auto-generated on first build)

License

GPL-2.0-only