The system /boot

While OSTree parallel installs deployments cleanly inside the /ostree directory, ultimately it has to control the system's /boot directory. The way this works is via the boot loader specification, which is a standard for bootloader-independent drop-in configuration files.

When a tree is deployed, it will have a configuration file generated of the form /boot/loader/entries/ostree-osname-checksum.serial.conf. This configuration file will include a special ostree= kernel argument that allows the initramfs to find (and chroot() into) the specified deployment.

At present, not all bootloaders implement the BootLoaderSpec, so OSTree contains code for some of these to regenerate native config files (such as /boot/syslinux/syslinux.conf based on the entries.