Error operation failed active console session exists for this domain

13 Jan 2020 — by ‘Maurits van der Schee’

In a previous post I have installed KVM (on Ubuntu 18.04) from the CLI on my Dell R720xd. In this post I will show how to adjust the GRUB config to enable the serial console in KVM and how to access it on the KVM CLI. This is great for fixing SSH connectivity issues and to do easy LUKS password entry during boot. In this post we will also explore how to allow access to the grub menu from the serial console.

Enable the console in GRUB

In order for the «console» command of «virsh» to work you need to modify the guest’s grub config.
In the guest run the following command:

sudo nano /etc/default/grub

Look for the line:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

and replace it with the following, or add this line if absent (on CentOS):

GRUB_CMDLINE_LINUX_DEFAULT="console=ttyS0"

On CentOS remove «rhgb quiet» from the line «GRUB_CMDLINE_LINUX» to ensure messages are shown.

On Ubunutu this is only effective after running «update-grub» using:

sudo update-grub

On CentOS you need to use the «grub2-mkconfig» command to update the grub config:

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

This should write the grub config to disk.

Connect to the console

To test that it works, we reboot the machine using:

sudo reboot

After rebooting the VM you can connect to the console using «virsh» by running:

virsh console maurits-cloud

Make sure to disconnect any graphical client (virt-manager) if you see this error message:

error: operation failed: Active console session exists for this domain

Console access is very good for emergency SSH connectivity fixes and LUKS password entry.

Grub menu via the console

You can also enable access to the grub menu using the console, but I feel this is not really necessary. The grub menu is already accessible from the VNC console. But if you do want this, then you should have the following entries in your «/etc/default/grub» file (change or add them):

GRUB_TIMEOUT=10
GRUB_TIMEOUT_STYLE=countdown
GRUB_TERMINAL="console serial"
GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1"
GRUB_CMDLINE_LINUX_DEFAULT="console=ttyS0"

Again apply and reboot with:

sudo update-grub
sudo reboot

You should now see the grub menu when you access the console using the «virsh console» command after pressing the escape (Esc) key during the countdown.

Next: Assigning a static IP address in KVM

In the next post I will walk you through setting up static IP addresses and hostnames for your KVM virtual machines. Hostnames allow you to connect to machines using their name instead of their (DHCP assigned) IP address. Static IP addresses are a requirement for doing port forwarding, a topic we will touch in another post in this blog series.

Click here to read the next article (on static ip addresses in KVM).

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virsh console YOUR_MACHINE Connect the virtual serial console for the guest

Syntax:

• virsh console YOUR_VM_NAME [devname] [--safe] [--force]
• Man page: https://www.libvirt.org/manpages/virsh.html#console

Connection examples[edit]

Connecting using VM name:

virsh console MACHINE_NAME
Connected to domain MACHINE_NAME
Escape character is ^]
error: operation failed: Active console session exists for this domain

Connecting using VM id. You can obtain it with virsh list

virsh console 3

Error when no argument is provided:

virsh console
error: command 'console' requires <domain> option

Enable serial console[edit]

You need to enable serial console in your VM machine.^[1]

1) Enable serial console on VM_MACHINE:

• sudo systemctl enable --now serial-getty@ttyS0.service

2) Connect to VM:

• virsh console MACHINE

Configure KVM server[edit]

virsh edit VM_NAME

<serial type='pty'>
 <source path='/dev/pts/0'/>
 <target type='isa-serial' port='0'>
   <model name='isa-serial'/>
 </target>
 <alias name='serial0'/>
</serial>
<console type='pty' tty='/dev/pts/0'>
 <source path='/dev/pts/0'/>
 <target type='serial' port='0'/>
 <alias name='serial0'/>
</console>

Ref: https://ravada.readthedocs.io/en/latest/docs/config_console.html

Quit console[edit]

Use CTRL + 5 to exit the console.^[2]

Kill old console[edit]

ps -ef | grep console
kill -9 {PID}

[edit]

• virsh ttyconsole
• virsh list
• virsh start
• virsh --connect
• virsh domdisplay VM_NAME
• virsh vncdisplay VM_NAME
• /var/log/libvirt/qemu/
• virsh edit
• Console
• virt-manager

See also[edit]

• Conneting: virsh [ console | ttyconsole | domdisplay | vncdisplay ], virsh --connect, virt-manager, virt-viewer, VNC
• virsh: Storage information, Connecting, Operations, Memory, Snapshots, Networking, CPU, release notes, virsh nodedev-list