Jeremy Katz (katzj) wrote,
Jeremy Katz
katzj

A week of livecd-tools hacking

In addition to spending a bit of time on my presentation for the Red Hat Summit on the state of the livecd tools and some of the surround stuff, I've also taken the time to go through and take care of some outstanding bugs and feature requests. Some of them were boring things for corner cases, but there are a couple of them that are a bit more interesting

The first is an addition to the persistence support which we added in Fedora 9. Instead of just keeping a snapshot (via dm-snapshot) of the changes to your filesystem in an overlay, you can now also set up something to be used as /home. By default, this will be a file on the same USB key that you put the Live OS on, but you can also specify to use a partition by uuid, label or device name. So you could potentially even have the /home located on a hard drive in your system and just always boot the OS off of USB. Also, due to a lot of the concerns around security and losing laptops or hard drives, etc, I've made it so that the default for the persistent /home is that it be encrypted with dm-crypt. This way, if you lose your USB key, your data at least won't be compromised. Watch for this as we start to do Fedora 10 images

The second is more targeted at a specific class of hardware. As you might have noticed, there are a growing number of Linux users who are choosing to run Linux on top of the current Intel-based Apple hardware. One of the features in Fedora 9 is native support for booting these machines directly from EFI rather than going through the "legacy" BIOS mode. (Side note -- this is often referred to as Boot Camp, but while the BIOS mode was added at the same time as Boot Camp's release, the BIOS mode was purely made possible by firmware changes and Boot Camp is the OS X app used for resizing your OS X install partition). The second piece is that these Intel based Macs do actually have support in their firmware for booting off of USB... the trick is that they can only do so via EFI and not via the legacy BIOS. So, I decided to make the changes necessary so that you can create a Live USB stick which boots on the Intel Macs. Unfortunately, it has a couple of limitations that aren't present in the general case.

  1. If you have one of the newer 64-bit capable Macs, you must use the 64-bit OS. We don't currently support booting the 32-bit OS from the 64-bit EFI
  2. Creating the USB key is currently a destructive process. One of the things about EFI is that it mandates the use of GPT for your partition table. And your USB key certainly came with an msdos partition table. I want to try to see if there's anything clever I can do, but I suspect this is just the way it rolls.
  3. Right now, you'll have to use a livecd created with git livecd-tools and it won't work with the Fedora 9 live images. But I should be able to put something into the livecd-iso-to-disk script to at least make this okay, I just haven't had the time today


Tags: fedora
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