Using recovery modes

Ubuntu Core docs UC20
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Ubuntu Core is inherently robust. But if data corruption issues do occur, even on boot or data partitions, it can still access a recovery mode to help repair, restore or reinstall an impaired device.

These recovery modes can be accessed in three different ways:

Recovery modes are available on Ubuntu Core 20 and later.

Device manufacturers may choose to implement alternative methods to access recovery functionality. These will be specific to those devices.

See Recovery modes for more details on each supported recovery mode, what they do, and how they can be used.

System mode selection menu

To access the system mode selection menu, start or reboot the device with the ‘1’ key held on a connected keyboard. If the chooser fails to launch, try pressing 1 repeatedly from boot. It needs to be captured by Ubuntu Core boot process.

After the initial boot process completes, a status screen will appear showing “System mode selection triggered. Proceed to select one of the available systems and actions.”

uc22-factory-reset

The menu system requires that you tab or cursor to highlight your chosen option. Ensure ‘OK’ is highlighted and press Enter to continue, after which you’ll be presented first with the recovery chooser and the option to either run normally, enter recovering mode, or reinstall.

Selecting an option followed by ‘Confirm’ will reboot the device into the selected mode (see below).

Recovery modes from snap reboot

Alongside using sudo snap reboot to reboot the system, the following arguments can be added to select a recovery mode with or without an additional system label for the target system:

  • --run
  • --install
  • --recover
  • --factory-reset

The recover and run modes are only available for the current system.

When called without a system label, reboot will use the current system to enter the given mode. System labels are listed with the snap recovery command:

$ sudo snap recovery
Label    Brand       Model                Notes
20201117 <user-name> ubuntu-core-20-amd64 current

To reboot the above system into recover mode, for example, enter the following:

$ sudo snap reboot --recover 20201117
Broadcast message from root@ubuntu (Wed 2020-11-25 13:15:51 UTC):

reboot scheduled to update the system
The system is going down for reboot at Wed 2020-11-25 13:25:51 UTC!

Reboot into "20201117" "recover" mode.

Using recovery keys

When using Full Disk Encryption, a device’s Trusted Platform Module (TPM) seals the encryption keys necessary to decrypt and boot the device.

These keys can be retrieved with the snap recovery --show-keys command:

$ sudo snap recovery --show-keys
recovery:  55055-39320-64491-48436-47667-15525-36879-32875

If a TPM becomes reinitialised or reconfigured, the TPM-sealed keys will be inaccessible and Ubuntu Core will not be able to decrypt and boot the device.

During boot, Ubuntu Core will instead ask for the recovery key for specific encrypted partitions. The same keys recovered with snap recovery --show-keys can then be entered to restore the device:

🔐 Please enter the recovery key for disk /dev/disk/by-partuuid/c7f7971b: (press TAB for no echo)

After entering a valid key, Ubuntu Core will decrypt the device, proceed with the boot, and restore the TPM from the recovered key. The recovery keys will remain the same and do not need to be retrieved again.

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Couple minor points I noticed:

  • The text mentions " If reinstall is selected". But as noted, the command line arg is --install, so the “reinstall” is a little confusing.
  • This is not strictly true " The snap reboot command requires both a label for the target system and an additional argument to specify the recovery mode to reboot into". You can still just run sudo snap reboot to reboot the current system normally
  • You can run just sudo snap reboot --recover to reboot into recovery mode without specifying the label of the recovery system (at least when there is only one recovery system).
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Thank you for looking through the document and for the corrections. I’ve updated the text to hopefully fix the erroneous text.

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A bit of nitpickery here, but are they “recover modes” or “recovery modes”? Yes, the individual mode is apparently “recover mode”, but what is the phrase to refer to the collection of them?

And, yes, I am that annoyingly pedantic.

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Not at all. It’s a good point. Neither are ideal really, but I think recovery modes works best, especially as this is also the name of the snap command. Thanks for all your help!

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Current implementation for “snap reboot” appears to include a “factory-reset” mode, which is not mentioned here.

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Good spot! We’re working on broader support for this right now, and we’ll have the docs published before the release of UC22 (mid- to late-May, currently).

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Also, should there be a mention of the “–run” option? I’m not even sure what that does. (That would be right at the top of the page, under “Snap reboot:”, which mentions only “–recover” and “–install”.)

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