===================
HVM troubleshooting
===================


HVM pauses on boot, followed by kernel error
--------------------------------------------


The HVM may pause on boot, showing a fixed cursor. After a while a
series of warnings may be shown similar to this:

.. code:: bash

      BUG: soft lockup - CPU#0 stuck for 23s! [systemd-udevd:244]



To fix this:

1. Kill the HVM.

2. Start the HVM

3. Press “e” at the grub screen to edit the boot parameters

4. Find the /vmlinuz line, and edit it to replace “rhgb” with
   “modprobe.blacklist=bochs_drm”

5. Press “Ctrl-x” to start the HVM



If this solves the problem then you will want to make the change
permanent:

1. Edit the file ``/etc/default/grub``.

2. Find the line which starts:

   .. code:: bash

         GRUB_CMDLINE_LINUX=



3. Remove this text from that line:

   .. code:: bash

         rhgb



4. Add this text to that line:

   .. code:: bash

         modprobe.blacklist=bochs_drm



5. Run this command:

   .. code:: bash

         grub2-mkconfig --output=/boot/grub2/grub.cfg





The HVM should now start normally.

Can't start an OS in an HVM / "Probing EDD (edd=off to disable!… ok" message
----------------------------------------------------------------------------


If you see a screen popup with SeaBios and 4 lines, last one being
``Probing EDD (edd=off to disable!... ok``, then enter the following
command from a ``dom0`` prompt:

.. code:: bash

      qvm-prefs <HVMname> kernel ""


HVM crashes when booting from ISO
---------------------------------


If your HVM crashes when trying to boot an ISO, first ensure that
``qvm-prefs <HVMname> kernel`` is empty, as shown above. If this doesn’t
help, then disable memory balancing and set the minimum memory to 2GB.

You can disable memory-balancing in the settings, under the “Advanced”
tab.

To give the VM a RAM of 2GB, open a terminal in ``dom0`` and enter:

.. code:: bash

      qvm-prefs <HVMname> memory 2000


Attached devices in Windows HVM stop working on suspend/resume
--------------------------------------------------------------


After the whole system gets suspended into S3 sleep and subsequently
resumed, some attached devices may stop working. To know how to make the
devices work, see :ref:`Suspend/resume Troubleshooting <user/troubleshooting/resume-suspend-troubleshooting:attached devices in windows hvm stop working on suspend\/resume>`.