Re: Where best to start

[Dave Hill <davehill@xxxxxxxxx>]

Hi Volker,

It's been a bit of a journey.  Lately I've been using pvhvm for my domUs.

The Guide is not wrong in any way. It's actually a bit of self-criticism to say it's dated, since I tried to update it not too long ago. I didn't edit this section mostly because it does work and I wasn't sure of current best practices.

Having said that, here are some of the concerns I have about it:

It uses pygrub. The script is super convenient but it's also opaque. The user can install Debian or Ubuntu or, at least according to apt show, older versions of CentOS. It is the most efficient approach for a beginner to get a PVM up and running. It means though that beginners don't acquire generic knowledge about installing distributions and writing/editing their own domU cfg files.

The Guide also says that pv-grub is not included in Debian, which is no longer the case and hasn't been for some time. I found the comments in the PvGrub2 page (https://wiki.xen.org/wiki/PvGrub2) about pygrub persuasive after I ran into one such a limitation.

Using pv-grub2 (or pvgrub2), is also a bit complicated though. The Guide refers the reader to a manual installation of Alpine Xen. The Alpine installation is a bit hard-core although it can be made to work. I also don't fully understand its boot process. Alpine's alpine.cfg file appears to rely on pv-grub2's former tolerance of GRUB1 menu.lst which I don't think works any longer.  I found myself dumped out to a GRUB prompt when I tried n fresh installation today. I previously learned to deal with that but it's not fun.

So, for a while I used pygrub, then I switched to pv-grub2. Then the PV drivers were added to the Linux kernel. The rationale for creating pv Linux guests was less clear. The Xen Project Best Practices page (https://wiki.xenproject.org/wiki/Xen_Project_Best_Practices) seems to recommend PVHVM.  So I switched my domU config files to:
    type=hvm
    xen_platform_pci=1

which I think accomplishes that. Installation of a domU is now almost identical to installing a distribution on hardware.

As may be apparent by this point, I consider myself to be a sort of permanent beginner at using Xen which is why I felt qualified to edit the Guide.

I'd really appreciate any comments you might have about any of this because I am just a beginner and may have it all or partially wrong.

In closing, let me say how fantastic I think Xen and its developers are! It's amazing to have such easy access to such a sophisticated system.

Dave

On 2020-06-02 7:11 a.m., Volker Janzen wrote:

Hi Dave,

It's dated (in particular, I wouldn't follow the advice there for building a PV Debian guest), but it contains the essentials to get Xen working generically.

how are you building your Xen guests?

Regards

     Volker