pi-topOS Recovery is the built-in recovery system of your pi-top device running pi-topOS.
Get back to a fresh install with no need to wipe the microSD card
Based on PINN/NOOBS, this is both a recovery operating system and integrated recovery application designed to run on startup. The recovery OS is a minified Linux environment (provided by buildroot). The recovery application is a shell script configured to run on recovery OS startup which can install pi-topOS from a USB memory device (actually anything that shows up in Linux via /dev/sd*.
If you are running pi-topOS Buster, then the files in /recovery are managed by the pt-recovery Debian package.
recovery contains the files of the recovery application, and the base recovery OS is taken from NOOBS Lite.
However, recovery.rfs is a special file that contains a squashed file system in it (An initramfs image containing various scripts and the GUI application). This is modified during packaging to instead provide an out-of-the-box automatic installer of pi-topOS via USB device.
Whilst pi-topOS Recovery will work on any clean FAT formatted SD card, it has been specifically designed to work with pi-topOS SD card images, which come with pi-topOS Recovery pre-installed.
Without an autoboot.txt file to redirect to during boot (e.g. containing boot_partition=5), init inside of the initramfs will set up the environment and wait 5 seconds for the user to press Enter to return to their OS's main partition. If no input is detected, then pt-os-installer will start.
pt-os-installer will wait a few seconds to give external devices a chance to initialise before trying to search for external storage devices. Any that are found will be probed for all zip files. Zip files are checked to see if a .img file is found within it, as well as pi-topOS's metadata file that contains the partition data for the image. This is what allows the installer to be able to reinstall the OS.
Installing pi-topOS can take a little while, but is usually comparable in write speed to using an SD card writer on another computer.
Once it has been installed, partitions are configured - e.g. modifying the filesystem table.
The OS install script will reboot into the newly installed pi-topOS partitions upon completion.
The files in this package make up the files in the first partition on a modern pi-topOS SD card (Buster onwards). See the pi-topOS Ansible playbook for more information about how the partitions are created/managed.
The recovery OS is triggered when it is unable to detect a partition to boot into, or when the Shift key is held down on boot, as with PINN and NOOBS.
For more information, check the pi-topOS documentation