---
lang: en
layout: doc
permalink: /doc/hvm-troubleshooting/
ref: 232
title: 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:

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

To fix this:

1. Kill the HVM.
1. Start the HVM
1. Press "e" at the grub screen to edit the boot parameters
1. Find the /vmlinuz line, and edit it to replace "rhgb" with "modprobe.blacklist=bochs_drm"
1. 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`.
1. Find the line which starts:

    ~~~
    GRUB_CMDLINE_LINUX=
    ~~~

1. Remove this text from that line:

    ~~~
    rhgb
    ~~~

1. Add this text to that line:

    ~~~
    modprobe.blacklist=bochs_drm
    ~~~

1. Run this command:

    ~~~
    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:

```sh
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:

```sh
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 [Suspend/resume Troubleshooting](/doc/suspend-resume-troubleshooting/#attached-devices-in-windows-hvm-stop-working-on-suspendresume).