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📦 Auto-growing disks in Vagrant: because 10 GB is never enough

Have you ever fired up a Vagrant VM, provisioned a project, pulled some Docker images, ran a build… and ran out of disk space halfway through? Welcome to my world. Apparently, the default disk size in Vagrant is tiny—and while you can specify a bigger virtual disk, Ubuntu won’t magically use the extra space. You need to resize the partition, the physical volume, the logical volume, and the filesystem. Every. Single. Time.

Enough of that nonsense.

🛠 The setup

Here’s the relevant part of my Vagrantfile:

Vagrant.configure(2) do |config|
  config.vm.box = 'boxen/ubuntu-24.04'
  config.vm.disk :disk, size: '20GB', primary: true

  config.vm.provision 'shell', path: 'resize_disk.sh'
end

This makes sure the disk is large enough and automatically resized by the resize_disk.sh script at first boot.

✨ The script

#!/bin/bash
set -euo pipefail
LOGFILE="/var/log/resize_disk.log"
exec > >(tee -a "$LOGFILE") 2>&1
echo "[$(date)] Starting disk resize process..."

REQUIRED_TOOLS=("parted" "pvresize" "lvresize" "lvdisplay" "grep" "awk")
for tool in "${REQUIRED_TOOLS[@]}"; do
  if ! command -v "$tool" &>/dev/null; then
    echo "[$(date)] ERROR: Required tool '$tool' is missing. Exiting."
    exit 1
  fi
done

# Read current and total partition size (in sectors)
parted_output=$(parted --script /dev/sda unit s print || true)
read -r PARTITION_SIZE TOTAL_SIZE < <(echo "$parted_output" | awk '
  / 3 / {part = $4}
  /^Disk \/dev\/sda:/ {total = $3}
  END {print part, total}
')

# Trim 's' suffix
PARTITION_SIZE_NUM="${PARTITION_SIZE%s}"
TOTAL_SIZE_NUM="${TOTAL_SIZE%s}"

if [[ "$PARTITION_SIZE_NUM" -lt "$TOTAL_SIZE_NUM" ]]; then
  echo "[$(date)] Resizing partition /dev/sda3..."
  parted --fix --script /dev/sda resizepart 3 100%
else
  echo "[$(date)] Partition /dev/sda3 is already at full size. Skipping."
fi

if [[ "$(pvresize --test /dev/sda3 2>&1)" != *"successfully resized"* ]]; then
  echo "[$(date)] Resizing physical volume..."
  pvresize /dev/sda3
else
  echo "[$(date)] Physical volume is already resized. Skipping."
fi

LV_SIZE=$(lvdisplay --units M /dev/ubuntu-vg/ubuntu-lv | grep "LV Size" | awk '{print $3}' | tr -d 'MiB')
PE_SIZE=$(vgdisplay --units M /dev/ubuntu-vg | grep "PE Size" | awk '{print $3}' | tr -d 'MiB')
CURRENT_LE=$(lvdisplay /dev/ubuntu-vg/ubuntu-lv | grep "Current LE" | awk '{print $3}')

USED_SPACE=$(echo "$CURRENT_LE * $PE_SIZE" | bc)
FREE_SPACE=$(echo "$LV_SIZE - $USED_SPACE" | bc)

if (($(echo "$FREE_SPACE > 0" | bc -l))); then
  echo "[$(date)] Resizing logical volume..."
  lvresize -rl +100%FREE /dev/ubuntu-vg/ubuntu-lv
else
  echo "[$(date)] Logical volume is already fully extended. Skipping."
fi

💡 Highlights

  • ✅ Uses parted with --script to avoid prompts.
  • ✅ Automatically fixes GPT mismatch warnings with --fix.
  • ✅ Calculates exact available space using lvdisplay and vgdisplay, with bc for floating point math.
  • ✅ Extends the partition, PV, and LV only when needed.
  • ✅ Logs everything to /var/log/resize_disk.log.

🚨 Gotchas

  • Your disk must already use LVM. This script assumes you’re resizing /dev/ubuntu-vg/ubuntu-lv, the default for Ubuntu server installs.
  • You must use a Vagrant box that supports VirtualBox’s disk resizing—thankfully, boxen/ubuntu-24.04 does.
  • If your LVM setup is different, you’ll need to adapt device paths.

🔁 Automation FTW

Calling this script as a provisioner means I never have to think about disk space again during development. One less yak to shave.

Feel free to steal this setup, adapt it to your team, or improve it and send me a patch. Or better yet—don’t wait until your filesystem runs out of space at 3 AM.

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