I have a Raspberry Pi 4B, and I installed Raspberry Pi OS onto a blank microSD card using the official imager. My understanding is that if I had used NOOBS, after installing the OS there would have still been a recovery mode that I could get into by pressing SHIFT on boot, but that doesn't seem to come with a regular OS image.
So my question is: is there a way to add a recovery mode to the existing SD card, so I can still edit /boot/config.txt from the Pi itself if I mess it up and can't boot the regular OS, rather than mounting the SD card from another computer and editing it that way? Can I just copy the recovery.* files from the NOOBS-lite distribution?
Edit: I finally found an explanation of how the NOOBS boot/partitioning works: https://github.com/raspberrypi/noobs/wiki/NOOBS-partitioning-explained So it might be possible to do an in-place addition of NOOBS/PINN on the SD card if I can resize/add the necessary partitions in the right order, but it seems like it'll be easier to:
- Do an external backup of the existing boot & root filesystem on the SD card in NOOBS format (using http://downloads.raspberrypi.org/raspios_armhf/ as a template)
- Reflash the SD card with just NOOBS/PINN
- Install the OS from the backup using NOOBS/PINN
