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Stefan Lasiewski
Asked: 2010-08-09 20:04:23 +0800 CST

What reason could prevent console output from "virsh -c qemu:///system console guest1"?

  • 772

I'm running KVM on a Ubuntu 10.04 host. The guest OS is also Ubuntu 10.04 .

I am attempting to connect to the guest using the 'console' command. It appears I can establish a connection, but I get no output.

$ sudo virsh -c qemu:///system console guest1
Connected to domain guest1
Escape character is ^]
(NOTHING HERE)
^]
$

I don't have a 'serial' device configured, but I do have these 'console' devices.

<console type='pty' tty='/dev/pts/2'>
  <source path='/dev/pts/2'/>
  <target port='0'/>
</console>
<console type='pty' tty='/dev/pts/2'>
  <source path='/dev/pts/2'/>
  <target port='0'/>
</console>

Are these sufficient for a console, or do I need a serial device as well?

What do I need to do in order to get the KVM console to work?

10.04 virtualization kvm

4 Answers

  1. Best Answer

    I'm fairly sure you do need to configure the guest to use a serial console. You need three things for this to work:

    1. give the guest a virtual serial device of type pty (for example by adding one in the virt-manager vm info page)

    2. tell the kernel to use that for its output, by adding boot parameters like serial=tty0 console=ttyS0,115200n8 into GRUB_CMDLINE_LINUX in /etc/default/grub; then run sudo update-grub

    3. (optional) put a getty on ttyS0 so that you get a login prompt

    See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=507650 for more.

    • 7

  2. One possibility is that your virtual machine does not have a serial console configured. 

    virsh dumpxml guest1

    will show if there is a serial console configured or not. There should be something similar as 

    <serial type='pty'>
<target port='0'/>
</serial>
    • 1

  3. Here it is very well explained:

    Serial console for Ubuntu server 10.04 KVM guests

    • 1

  4. I just ran into this.

    Here is what I have inthe XML config on the host (running KVM):

    <serial type='pty'>
  <source path='/dev/pts/0'/>
  <target port='0'/>
</serial>
<console type='pty' tty='/dev/pts/0'>
  <source path='/dev/pts/0'/>
  <target port='0'/>
</console>

    I also had to add the following in /etc/default/grub.conf in the VM (append to the "kernel" command):

    kernel ..... serial=tty0 console=ttyS0,115200n8

    Finally I secured the ttyS0 by adding "/etc/securetty" to enable root login from here

    vi /etc/securetty
ttyS0

    You might need to muck with your getty settings (as described by the other answer) as well

    Hope this helps

    • 1