Vagrant and Virtualbox: a debugging story

Recently, I ran into VirtualBox bug #10077:APIC Bug. I wanted to help out so I had to enable console logging to my machine to give useful output. For that same reason, I started setting console=ttyS0 console=tty0 ignore_loglevel to kernel options in grub.cfg on my vagrant-baseboxes.

The apic bug did not occur on every startup so I had to do a lot of them before I got it right. This tempted me to get the console redirect feature of VirtualBox working from within a Vagrantfile. Well, in the end, it’s not that hard…

config.vm.define :base6 do |base_config|
    base_config.vm.customize [
      "modifyvm", :id, "--name", "CentOS 6 x86_64 Base",
      "--uart1", "0x3F8", "4", 
      "--uartmode1", "file", "/tmp/base6-console.log"

Note that this file gets overwritten every time you vagrant up your box. So if you want time stamped logs, you’ll have to introduce some magic (do let me know if you do ;))

Reducing vagrant box size

Here are some tricks I use to make my vagrant boxes as small as possible:


Booting in single user mode:

I boot in single user mode since it will prevent running services that could output logs. I do this because I zero out all my logs before packaging the box.


After updating any package, run yum clean (or the apt equivalent).

When booted in single user mode, don’t forget to start-up your network before updating.

When updating kernels, install the kernel packages, reboot and remove the old kernel packages that are no longer in use. Remember to re-install the VirtualBox add-ons too after a kernel update.


After doing whatever you need to do with the box, I do some rather nasty stuff to make sure the box uses as little as possible place. If you are using a RAW hard-disks, these might be a bad idea (stuff gets BIG).

  • Zero out all remaining unused disk space
  • Zero out the swap
  • Clear out all log files (I just make them empty, I do NOT delete them)

(You can find this script – or an older version in /root/tools/ on my newer vagrant boxes.)

cat - << EOWARNING
WARNING: This script will fil up your left over disk space.
You should NOT do this on a running system.
This is purely for making vagrant boxes damn small.
Press Ctrl+C within the next 10 seconds if you want to abort!!
sleep 10;
echo 'Cleanup bash history'
[ -f /root/.bash_history ] && rm /root/.bash_history
[ -f /home/vagrant/.bash_history ] && rm /home/vagrant/.bash_history
echo 'Cleanup log files'
find /var/log -type f | while read f; do echo -ne '' > $f; done;
echo 'Whiteout root'
count=`df --sync -kP / | tail -n1  | awk -F ' ' '{print $4}'`; 
let count--
dd if=/dev/zero of=/tmp/whitespace bs=1024 count=$count;
rm /tmp/whitespace;
echo 'Whiteout /boot'
count=`df --sync -kP /boot | tail -n1 | awk -F ' ' '{print $4}'`;
let count--
dd if=/dev/zero of=/boot/whitespace bs=1024 count=$count;
rm /boot/whitespace;
swappart=`cat /proc/swaps | tail -n1 | awk -F ' ' '{print $1}'`
swapoff $swappart;
dd if=/dev/zero of=$swappart;
mkswap $swappart;
swapon $swappart;

Furthermore – about this script – USE IT AT YOUR OWN RISK