Alternative Boot Loaders

[Matt Darcy]

Colin Watson wrote:
> On Fri, May 02, 2008 at 04:40:49PM +0100, Matt Darcy wrote:
>   
>> I'm trying to establish the reasoning behind including alternative boot 
>> loaders such as lilo on the ubuntu alternative and server cds ?
>>
>> Was this a technical decision ?
>> Was this a policy decision ?
>>
>> could someone please explain the decision and the reasons behind it.
>>     
>
> This was a technical decision (inherited from Debian, but very much
> supported by me). The circumstances in which the installer will install
> LILO are precisely as follows:
>
>   * /boot is on an LVM volume
>   * /boot is on an XFS file system (and the
>     grub-installer/install_to_xfs debconf question was not explicitly
>     preseeded to true)
>   * the grub-installer/skip debconf question was explicitly preseeded to
>     true
>
> The XFS item has been disputed from the start, and I can only repeat
> what I've always said regarding it. The problem here is that XFS skates
> close to the edge of what the POSIX specification allows a file system
> to do; in particular it cannot be forced to write data to disk by any
> action short of unmounting and remounting the file system (or possibly
> remounting the file system read-only, but I seem to remember that that
> was also problematic). GRUB requires that data be physically on disk in
> order for grub-install to work. To answer a frequently asked question
> up-front, 'xfs_freeze -f' at least used not to be sufficient to
> guarantee that data had been written to disk; I tested this extensively
> some time ago.
>
> This problem is a race condition, and so it is entirely possible that
> some users may never see it, while other users will always see it, and
> still others will randomly see it or not. Installing LILO, whatever its
> user interface deficiencies, is much better than the boot loader
> installation process crashing.
>
> Ubiquity does not at present support installing LILO (which is a bug
> we'll need to fix at some point). In this environment, LVM partitioning
> is not yet supported, and attempting to put /boot on an XFS file system
> will warn you that this may cause problems.
>
> Regards,
>
>   
Colin,

two excellent mails, thank you.

The information on the xfs limitations and potential race condition 
senario with data not actually being written to the disk is a new slice 
of information for me.

Thank you for clarifying on both counts.

Matt