KarmicGrub2

Differences between revisions 5 and 6
Revision 5 as of 2009-06-15 10:54:52
Size: 5768
Editor: 82-69-40-219
Comment: UI work; testing
Revision 6 as of 2009-06-15 11:19:34
Size: 6344
Editor: 82-69-40-219
Comment: migration
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== User stories ==

== Assumptions ==
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{{{
* grub1 -> grub2 upgrade
(Completion of the tasks identified here is not mandatory for the completion of this specification. We have a migration process already that minimally works, and it is acceptable to consider only new installations as long as we do not actively break the upgrade case. However, improvements here are expected to reduce confusion.)
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 Go for chainloading grub2 in the upgrade
 Grub 2 for new installation
 Karmic +1 to drop grub 1?
Although we do not expect to migrate all existing Ubuntu installations to GRUB 2 at this point (upgrading the boot loader being an inherently risky operation), only install it by default for new installations, we would still like to make the upgrade process as smooth as possible. It is already reasonably straightforward thanks to work done by Debian: when you install the `grub-pc` package, you get a "Chainload into GRUB 2" menu item which lets you test whether GRUB 2 will work, and an `upgrade-from-grub-legacy` command that you can run to switch the primary boot loader to GRUB 2.
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 Make update-grub only update grub2 A smoother approach might be to use GRUB Legacy's `grub-reboot` to arrange to boot into GRUB 2 with zero timeout, and if this works then either use `grub-set-default` to arrange to chainload GRUB 2 by default with zero timeout (cf. http://grub.enbug.org/Hiddenmenu) or run `upgrade-from-grub-legacy`. If we chainload, then GRUB Legacy's stage 1.5 and stage 2 remain integral parts of the boot process, and must not be removed.
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 Do automatic change to grub 2: Remember that the mapping between Linux device names and GRUB device names in `/boot/grub/device.map` may not be correct. In any migration process, it is important not to rely on this, since that might result in incorrectly overwriting boot sectors that do not already belong to GRUB.
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   - detect chainloaded from grub 1
   - then install grub 2
 change menu.lst in grub 1 - with zero timeout and chainload grub2
        Robert Millan points to http://grub.enbug.org/Hiddenmenu to implement behaviour similar to what we used in GRUB 1.
(In the UDS session, we also discussed a problem that was believed to exist whereby `grub` would remove `/boot/grub/menu.lst` on purge. This is in fact not true; it only removes the record of that file in `ucf`, which is fine. This comment is included so that we do not need to have the discussion again!)
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    leave stage1.5 (don't scrub it)
    - grub loads grub stage 1.5 (in 32K between MBR and first partition if installed in MBR, or in the boot sector of the partition if installed in a partition)
    - then loads grub stage 2 from fs
    - then chainloads grub2 (2nd stage)

    Note: do not remove grub stage1.5 + stage2

   - device map (hdX,Y) may not 100% correct on some systems

  * purge process of grub1 removes menu.lst - this is an issue that needs fixing.
   - dependency issues:
     make sure postrm is removed from grub
     grub-pc replaces grub
     use breaks to stop clobbering of menu.lst on purge
}}}
  
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== Unresolved issues ==

This should highlight any issues that should be addressed in further specifications, and not problems with the specification itself; since any specification with problems cannot be approved.

Summary

Move to GRUB 2 as the default boot loader.

Release Note

This section should include a paragraph describing the end-user impact of this change. It is meant to be included in the release notes of the first release in which it is implemented. (Not all of these will actually be included in the release notes, at the release manager's discretion; but writing them is a useful exercise.)

It is mandatory.

Rationale

This should cover the _why_: why is this change being proposed, what justifies it, where we see this justified.

Design

By and large, GRUB 2 appears to be in a reasonably good state now, after a long period when we were unable to seriously contemplate a switch. There are some things to fix, of course, but for the most part these look tractable. The kernel team did extensive testing, which suggests a strong performance.

Implementation

General issues

There are still some minor issues to fix; Ubuntu branding to the configuration file is not quite right.

LVM: Currently GRUB cannot deal with /boot being on LVM, so we need to use LILO in that case. We will check whether GRUB 2 can deal with /boot on LVM (it definitely has code to deal with LVM, so should be a simple matter of configuration), and if so remove the need to ship LILO on our CD images.

XFS: In the past, GRUB had a race condition installing on XFS. This was fixed in GRUB Legacy; ensure that it's fixed in GRUB 2 as well.

EFI/UEFI: We will check support on Intel-based Macs and on x86 PCs with EFI support. (Supply of hardware for the latter case is still rather limited.)

PowerPC: While it is not required for this specification to be considered implemented, it would be useful for PowerPC porters to look at the existing OpenFirmware support and see if we can switch from yaboot. This will need changes in grub-installer and ubiquity.

UI work

On systems with multiple operating systems installed, we would like to be able to offer a convenient desktop interface (e.g. via the "Restart..." menu item) to determine which OS will be started at the next boot. GRUB Legacy had grub-reboot and grub-set-default which could be used for this: grub-reboot made a single-shot change, while grub-set-default made a permanent change. While GRUB 2 does not quite have this packaged as neatly yet, the primitives are in place (grub-editenv, etc.) and it is expected to be simple to put them together. The upstream developers would be interested in integrating this if we beat them to it.

FIXME: DX team to add exact requirements here

By default, we will hide the GRUB menu, but need to make it possible to access it when required by holding down a key. We need to make sure that the key involved is distinct from that used to instruct usplash to show detailed boot output, and also distinct from typical keys used to access firmware setup.

  • GRUB Legacy: timeout, interrupted by holding Escape
  • PC BIOSes: typical keys include Shift, Delete, and F12, but this is usually accompanied by a message such as "Press Shift to enter CMOS Setup" which disappears before the BIOS is finished, so it is not so important to avoid clashes with this
  • Apple Mac: Alt (Option) accesses built-in firmware boot menu; no visual indication of when this should be pressed
  • usplash: not implemented yet, so whatever we like

Consensus appears to be to use Shift to access the GRUB 2 menu.

Migration

(Completion of the tasks identified here is not mandatory for the completion of this specification. We have a migration process already that minimally works, and it is acceptable to consider only new installations as long as we do not actively break the upgrade case. However, improvements here are expected to reduce confusion.)

Although we do not expect to migrate all existing Ubuntu installations to GRUB 2 at this point (upgrading the boot loader being an inherently risky operation), only install it by default for new installations, we would still like to make the upgrade process as smooth as possible. It is already reasonably straightforward thanks to work done by Debian: when you install the grub-pc package, you get a "Chainload into GRUB 2" menu item which lets you test whether GRUB 2 will work, and an upgrade-from-grub-legacy command that you can run to switch the primary boot loader to GRUB 2.

A smoother approach might be to use GRUB Legacy's grub-reboot to arrange to boot into GRUB 2 with zero timeout, and if this works then either use grub-set-default to arrange to chainload GRUB 2 by default with zero timeout (cf. http://grub.enbug.org/Hiddenmenu) or run upgrade-from-grub-legacy. If we chainload, then GRUB Legacy's stage 1.5 and stage 2 remain integral parts of the boot process, and must not be removed.

Remember that the mapping between Linux device names and GRUB device names in /boot/grub/device.map may not be correct. In any migration process, it is important not to rely on this, since that might result in incorrectly overwriting boot sectors that do not already belong to GRUB.

(In the UDS session, we also discussed a problem that was believed to exist whereby grub would remove /boot/grub/menu.lst on purge. This is in fact not true; it only removes the record of that file in ucf, which is fine. This comment is included so that we do not need to have the discussion again!)

Test/Demo Plan

Significant testing on reasonably recent hardware has already been performed, but testing on older hardware will be important. Some ideas for this include:

  • - Canonical's hardware certification farm - Xubuntu community may well have more legacy hardware - close coordination with Debian (expected to move to GRUB 2 for Squeeze)

    - further promulgation of KernelTeam/Grub2Testing

See also

Previous (misnamed) specification in this series: FoundationsTeam/Specs/Grub2ByDefault

Kernel team testing page


CategorySpec

FoundationsTeam/Specs/KarmicGrub2 (last edited 2009-09-04 18:13:16 by 82-69-40-219)