Early patching is a development feature. Please don't use it for your regular Tails!

The goal of this page is to give you hint on how to speed up your development by avoiding to build an image. Rebuilding an image is unfortunately very slow and resource-intensive, which makes the Developer Experience unpleasant.

The idea of early-patch is very simple: at boot time, if a specific boot option is added, a directory is shared between the host and the Tails VM, and mounted at /mnt/. Since mounting in itself is not very useful, you can configure a program to run at initramfs-time.


Configure libvirt

Please add this to your domain definition, inside the <devices> tag:

<filesystem type='mount' accessmode='passthrough'>
  <source dir='/path/to/your/tails/checkout/'/>
  <target dir='src'/>

The word src is a magic constant. Do not change it.

Create an install script

Let's say that you are iterating on improvements for config/chroot_local-includes/etc/NetworkManager/dispatcher.d/. You might want to put a script such as this in ./hook at the root of the shared directory:

# this will typically be '/root'; but more generally, it is the root of the system.
find "$root/etc/NetworkManager/dispatcher.d/" -type f -exec rm {} \;
find "$root/mnt/config/chroot_local-includes/etc/NetworkManager/dispatcher.d/" -type f -exec cp {} "$root/etc/NetworkManager/dispatcher.d/" \;

and make it executable. Remember: you are running at initramfs-time, which is why you have to take care of the /root prefix. For the same reason, you should write in POSIX shell, not bash.


Run your VM, and add early_patch to the kernel cmdline.


Most important implementation bits are at config/chroot local-includes/usr/share/initramfs-tools/scripts/init-bottom/early patch