virt-install doesn't automatically default to Xen in Trusty

I will have to play around with that and check the newer version of libvirt. But it might be a fundamental problem. For exclusive technologies like KVM and Xen, I guess the tools could make a decission at run-time. It would need to be runtime because it is always possible to boot the same install with or without the Xen hypervisor. So the same installation could be using KVM or Xen as hypervisor.
Having said that, it might be possible that it depends on whether libvirt is installed before or after Xen (and maybe needs to be running in dom0 to make the other choice).

Stefan, did you ever reach any conclusions about this?

Hi Serge, no sorry. Actually this one I totally forgot. Hm, I don't think libvirt upstream would want to make changes to the URI concept. And since on an initial install Xen HV is not running, we cannot set any static default. Which would be wrong anyway as it is possible to switch between Xen and non-Xen or KVM mode on boot.

Hm, what would you think about adding the following file for /etc/profile.d to our package? Probably it would also work when I would not set any environment in the no-Xen case.

As the original report says, this doesn't seem to be an upstream issue. As I reported there, Fedora with libvirt 1.2.5 didn't have this problem; and on the Xen4CentOS packages, neither libvirt 0.10 nor libvirt 1.2.10 had this problem. In all cases, if you booted under Xen, virsh would find Xen without any extra hand-holding. In the case of Xen4Centos libvirt 1.2.10 packages, I can see that there are no patches changing any defaults.

It seems likely that somewhere Ubuntu has actually added something which is changing the default URI to KVM.

Hi George, hm, could it be that for the cases where that works libvirt had been installed after booting into Xen dom0? I had a quick look at the code we have in Trusty right now and the library code handling the URI basically checks LIBVIRT_DEFAULT_URI environment variable, or uri_default config variable, or falls back to qemu (in that order) [src/libvirt.c:virConnectGetDefaultURI]. This is the same as in the upstream git repo (pulled just now).
For virsh it seems looking only for the environment variable for a default or otherwise call the library with NULL which then again does the resoving as described above.

For UBUNTU (Trusty at least) the uri_default in the config file is commented out (so without anything in the environment defaulting to qemu sounds expected). Do you have something set (either in the environment or in the config file) for other distros?

And just in case you wonder why I typed Ubuntu in all capital letters... old farts brain being used to type that as a tag in git commit messages...

/etc/profile.d approach looks good to me.

This bug was fixed in the package libvirt - 1.2.12-0ubuntu12

---------------
libvirt (1.2.12-0ubuntu12) vivid; urgency=low

  * Add profile script to automatically set the default URI based on
    the currently running hyperisor (Xen or KVM/Qemu).
    (LP: #1334749)
 -- Stefan Bader <email address hidden> Tue, 14 Apr 2015 09:02:52 -0500