Installing Stacker¶

Stacker is a single static binary tool with most of the dependencies built into the binary. Stacker, however, depends on specific kernel capabilities and system tools to provide various features.

wget https://github.com/project-stacker/stacker/releases/latest/download/stacker
chmod +x ./stacker
sudo cp ./stacker /usr/bin/stacker
stacker --version
stacker check

Kernel dependencies¶

Stacker requires overlayfs backend. That works with any kernel >= 4.14. However, for unprivileged usage, the overlayfs backend requires a new kernel change available on all kernels >= 5.8.

Some distributions may have ported these patches into older versions of their kernels. For example, Ubuntu 20.04 and 22.04 kernels already have these patches.

Stacker includes checks to ensure that it can run with all these requirements, and will fail if it can't perform a function it should be able perform.

stacker check && echo "stacker is ready to use!"

Overlay filesystem¶

An underlying overlayfs cannot back stacker because the stacker needs to create whiteout files, and the kernel (rightfully) forbids manual creation of whiteout files on overlay filesystems. No additional userspace dependencies are required to use the overlayfs backend.

Unprivileged setup¶

Running stacker as an unprivileged user requires stacker to run as part of a user namespace owned by the user that executed the command. Stacker will map 65k user and group IDs to meet the POSIX standard. So, to run stacker, the user's /etc/sub{u,g}id should be configured with enough UIDs to map components correctly. This configuration can be run automatically via stacker unpriv-setup.

sudo stacker unpriv-setup
cat /etc/subgid
cat /etc/subuid

Squashfs support¶

In order to generate squashfs images, stacker invokes the mksquashfs binary. This binary needs to be installed and available in $PATH.

sudo apt-get install -y squashfs-tools