Troubleshooting KVM Guest Boot Failures on Ubuntu Oneiric: Console Hangs and High CPU Usage


2 views

When working with KVM virtualization on Ubuntu Oneiric Server (AMD64), you might encounter situations where guests appear to start successfully but fail to provide console output. The typical symptoms include:

  • Guest shows as "running" in virsh list
  • Console connection hangs after displaying the escape character message
  • Remote connections only show "Booting from Harddisk"
  • Intermittent high CPU usage by KVM process
  • Inability to perform clean shutdown (requires destroy command)

The Ubuntu Oneiric (11.10) era had several known issues with KVM:

# Check your current KVM version
kvm --version
QEMU PC emulator version 0.14.1 (qemu-kvm-0.14.1+noroms), Copyright (c) 2003-2008 Fabrice Bellard

Key potential causes:

  1. Missing or misconfigured serial console
  2. Storage driver compatibility issues with qcow2
  3. ACPI power management conflicts
  4. Outdated seabios implementation

For the serial console issue, edit your guest XML definition:

<serial type='pty'>
  <target port='0'/>
</serial>
<console type='pty'>
  <target type='serial' port='0'/>
</console>

For storage issues, try converting the image format:

qemu-img convert -f qcow2 -O raw myguest.qcow2 myguest.raw

When standard installation fails, try this manual approach:

virt-install \
--name myguest \
--ram 2048 \
--disk path=/var/lib/libvirt/images/myguest.qcow2,size=12 \
--vcpus 2 \
--os-type linux \
--os-variant ubuntuoneiric \
--network bridge=br0 \
--graphics none \
--console pty,target_type=serial \
--location 'http://archive.ubuntu.com/ubuntu/dists/oneiric/main/installer-amd64/' \
--extra-args 'console=ttyS0,115200n8 serial'

Enable full QEMU logging:

# Edit libvirtd.conf
log_level = 1
log_outputs="3:file:/var/log/libvirt/libvirtd.log"

# Restart libvirt
service libvirtd restart

Monitor boot process:

virsh dumpxml myguest | grep 'lt;serial'
tail -f /var/log/libvirt/qemu/myguest.log

The package combination shown has known quirks:

# Recommended alternative packages
sudo apt-get install \
qemu-kvm=0.15.0-1ubuntu4 \
libvirt-bin=0.9.8-2ubuntu1 \
python-libvirt=0.9.8-2ubuntu1 \
virtinst=0.600.0-1ubuntu1

Remember to purge conflicting packages:

sudo apt-get remove --purge qemu-system qemu-user

Before declaring defeat, verify:

# KVM hardware acceleration
kvm-ok

# User permissions
groups | grep libvirt

# Kernel modules
lsmod | grep kvm

When attempting to launch KVM guests on Ubuntu Oneiric Server (64-bit AMD), I encountered a situation where virtual machines would appear to start (showing as "running" in virsh list) but fail to produce any console output beyond the initial boot message. The key symptoms were:

  • Blank console output when connecting via virsh console
  • Only "Booting from Harddisk" message visible in VNC
  • Inability to properly shut down guests (requiring destroy command)
  • Occasional 100% CPU usage spikes

First, let's examine the VM configuration more closely. The vmbuilder command used:

vmbuilder kvm ubuntu \
--suite oneiric --flavour virtual --arch amd64 \ 
--libvirt qemu:///system \
--ip 192.168.0.100 \
--hostname myguest \
--part vmbuilder.partition \ 
--user adminUser --name fullname --pass defaultPass \
--addpkg apache2 [...other packages...] \
--mem 2048 \
--bridge br0

And the alternative virt-install approach:

virt-install \ 
--connect qemu:///system -n myguest -r 2048 -f myguest.qcow2 \
-s 12 -c ubuntu-11.10-server-amd64.iso --vnc --noautoconsole --os-type linux \
--os-variant ubuntuOneiric --accelerate --network=network:default

To properly diagnose this issue, several verification steps are essential:

  1. Check the VM XML configuration: 
    virsh dumpxml myguest

    Pay special attention to the console and serial device configuration.

  2. Verify the disk image: 
    qemu-img info myguest.qcow2

    Ensure the disk format is correct and the backing file (if any) is accessible.

  3. Examine alternative logs: 
    sudo cat /var/log/libvirt/qemu/myguest.log

    This often contains more detailed boot information than libvirt.log.

After thorough testing, I found these approaches resolved similar issues:

1. Forcing Serial Console Configuration

Add explicit console configuration to your vmbuilder command:

--serial pty --console pty

Or manually edit the domain XML:

<serial type='pty'>
  <target port='0'/>
</serial>
<console type='pty'>
  <target type='serial' port='0'/>
</console>

2. Alternative Boot Methods

Try booting directly from ISO first to isolate the issue:

virt-install \
--name myguest-test \
--ram 2048 \
--disk path=/var/lib/libvirt/images/myguest-test.qcow2,size=12 \
--vcpus 2 \
--os-type linux \
--os-variant ubuntuOneiric \
--network network:default \
--graphics vnc \
--cdrom ubuntu-11.10-server-amd64.iso \
--noautoconsole

3. Verifying KVM Acceleration

Check that KVM acceleration is properly enabled:

kvm-ok
# Expected output:
# INFO: /dev/kvm exists
# KVM acceleration can be used

# Check CPU virtualization flags:
egrep -c '(vmx|svm)' /proc/cpuinfo
# Should return > 0

When console connections fail, try these debugging commands:

# Check if getty is running on the guest
ps aux | grep getty

# Alternative connection method using socat:
sudo socat UNIX-CONNECT:/var/lib/libvirt/qemu/myguest-serial0 STDIO

After troubleshooting, this configuration proved reliable:

virt-install \
--name myguest-working \
--ram 2048 \
--disk path=/var/lib/libvirt/images/myguest-working.qcow2,size=12,bus=virtio \
--vcpus 2 \
--os-type linux \
--os-variant ubuntuOneiric \
--network bridge=br0 \
--graphics none \
--console pty,target_type=serial \
--location 'http://archive.ubuntu.com/ubuntu/dists/oneiric/main/installer-amd64/' \
--extra-args 'console=ttyS0,115200n8 serial'

The key differences being the explicit serial console configuration and using the network installer rather than a local ISO.