[TUTORIAL] Proxmox LXC to VM Converter

[ArMaTeC]

A robust Bash toolkit that converts Proxmox LXC containers into fully bootable QEMU/KVM virtual machines — directly on your Proxmox VE host. Includes a companion disk-shrink script and handles disk creation, filesystem copy, kernel/GRUB installation, networking reconfiguration, and VM provisioning automatically.

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Table of Contents​

• Scripts
• Features
• Supported Distros
• Requirements

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Scripts​

This project includes two scripts:

Script	Purpose
lxc-to-vm.sh	Converts an LXC container into a bootable VM. Main script.
shrink-lxc.sh	Shrinks an LXC container's disk to used space + headroom. Standalone or use --shrink in lxc-to-vm.sh.

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Features​

Conversion (lxc-to-vm.sh)​

• One-command conversion — turn any LXC into a bootable VM
• Multi-distro support — Debian, Ubuntu, Alpine, CentOS/RHEL/Rocky, Arch Linux (auto-detected)
• BIOS & UEFI boot — MBR/SeaBIOS (default) or GPT/OVMF with --bios ovmf
• Integrated disk shrink — --shrink shrinks the LXC disk before conversion, auto-sets disk size
• Dry-run mode — preview every step without making changes (--dry-run)
• Network preservation — keep original network config with --keep-network, or replace with DHCP on ens18
• Auto-start & health checks — boot the VM and verify guest agent, IP, and reachability (--start)
• Post-conversion validation — automatic 6-point check (disk, boot order, network, agent, EFI)
• Interactive & non-interactive modes — use CLI flags for scripting or answer prompts manually
• Auto-dependency installation — missing tools (parted, kpartx, rsync, etc.) installed automatically
• Input & storage validation — catches invalid IDs, missing storage, format errors before work begins
• Smart disk space management — checks available space, auto-selects mount points with room, explains LVM vs filesystem constraints
• Custom working directory — --temp-dir to place the temporary disk image on any mount point
• LXC config inheritance — memory, CPU cores pulled from the source container config
• Serial console support — enables ttyS0 serial console for Proxmox terminal access
• Colored output — color-coded progress messages (auto-disabled when piped)
• Full logging — all operations logged to /var/log/lxc-to-vm.log
• Safe cleanup — trap-based cleanup removes temp files and loop devices on exit or error
• Wizard mode — interactive TUI with progress bars and guided setup (--wizard)
• Parallel batch processing — run N conversions concurrently (--parallel N)
• Pre-flight validation — comprehensive checks without converting (--validate-only)
• Cloud/remote export — export VM disks to S3, NFS, or SSH destinations (--export-to)
• VM template creation — convert to Proxmox template with optional sysprep (--as-template)
• Auto-rollback — automatically restore container if conversion fails (--rollback-on-failure)
• Configuration profiles — save and reuse common conversion settings (--save-profile, --profile)
• Resume capability — resume interrupted conversions from partial state (--resume)
• Auto-cleanup — destroy original LXC after successful conversion (--destroy-source)

Disk Shrinker (shrink-lxc.sh)​

• Shrinks LXC disks to actual usage + configurable headroom
• Smart minimum detection — queries resize2fs -P for the true filesystem minimum size
• Auto-retry — if resize2fs fails, automatically increments by 2GB and retries (up to 5 attempts)
• Multi-backend — supports LVM-thin, LVM, directory (raw/qcow2), and ZFS storage
• Dry-run mode — preview the shrink plan without making changes
• Safety confirmation — prompts before destructive operations
• Prints ready-to-use conversion command after shrinking

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Supported Distros​

Distro Family	Detected IDs	Package Manager	Notes
Debian/Ubuntu	debian, ubuntu, linuxmint, pop, kali	apt	Primary target, most tested
Alpine	alpine	apk	OpenRC init system configured automatically
RHEL/CentOS	centos, rhel, rocky, alma, fedora	yum/dnf	Kernel + GRUB2
Arch Linux	arch, manjaro, endeavouros	pacman	Kernel + GRUB

Distro is auto-detected from /etc/os-release inside the container. The script uses the appropriate package manager and bootloader installation commands for each family.

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Requirements​

Requirement	Details
Proxmox VE	Version 7.x, 8.x or 9.x
Source LXC	Debian, Ubuntu, Alpine, CentOS/RHEL/Rocky, or Arch based container
Root access	Scripts must run as root on the Proxmox host
Free disk space	Filesystem space ≥ disk image size (LVM/ZFS storage cannot be used as temp space — see Disk Space Management)
Network	Internet access (to install kernel/GRUB packages inside chroot)

Dependencies (auto-installed by lxc-to-vm.sh)​

• parted — disk partitioning
• kpartx — partition mapping for loop devices
• rsync — filesystem copy
• e2fsprogs — ext4 formatting and filesystem tools (mkfs.ext4, resize2fs, e2fsck)
• dosfstools — FAT32 formatting for UEFI ESP (only when using --bios ovmf)

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For more details see https://github.com/ArMaTeC/lxc-to-vm​

 

[ArMaTeC]

"Bug Fix Edition" — Critical boot and cleanup fixes

Fixed FEATURE_C12 Boot Error — Properly disable metadata_csum and related ext4 features to prevent initramfs boot failures
Fixed Cleanup Trap — Properly unmount virtual filesystems (dev/pts, dev, proc, sys) before temp directory removal
Added Metadata Checksum Verification — Verify metadata_csum is actually disabled before proceeding with conversion
Improved tune2fs Error Handling — Fail conversion if ext4 feature disabling fails (no silent failures)

https://github.com/ArMaTeC/lxc-to-vm/releases/tag/v6.0.2

Full Changelog: 6.0.0...v6.0.2

 

[Chris Walken]

I wanted to migrate my OpenClaw LXC to a VM and asked Perplexity for advice. The first method that came up was your script. It took only a few minutes, and the VM was ready and running without any issues. Well done!