How to check and restore QEMU Guest Agent?

QEMU Guest Agent is a daemon program that is installed on a VM. QEMU Guest Agent provides execution of commands on VMs and information exchange between VMs and the cluster node.

VMmanager uses QEMU Guest Agent to change network settings without rebooting. If the QEMU Guest Agent is unavailable for the platform for five minutes, VMmanager will reboot the VM to apply the settings.

To manage VM with CentOS OS, guest-exec function should be enabled in QEMU Guest Agent.

To avoid an unplanned reboot of the VM, you can check the status of the QEMU Guest Agent before changing the settings. This can be done on a VM or the cluster node.

Diagnostics on the VM

Connect to the VM via SSH.

Define the status of the QEMU Guest Agent:

systemctl status qemu-guest-agent

Examples of responses:

QEMU Guest Agent is running

● qemu-guest-agent.service - QEMU Guest Agent
   Loaded: loaded (/usr/lib/systemd/system/qemu-guest-agent.service; enabled; vendor preset: enabled)
   Active: active (running) since Вт 2021-08-10 05:25:54 UTC; 1 weeks 3 days ago

QEMU Guest Agent is stopped

● qemu-guest-agent.service - QEMU Guest Agent
   Loaded: loaded (/usr/lib/systemd/system/qemu-guest-agent.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Пт 2021-08-20 06:27:16 UTC; 2s ag

QEMU Guest Agent is not installed

Unit qemu-guest-agent.service could not be found.

Diagnostics on the cluster node

Connect to the cluster node via SSH.
Define the status of the QEMU Guest Agent:
```
virsh qemu-agent-command <vm_id>_<vm_name> '{"execute": "guest-info", "arguments": {}}'
```
Comments to the command
<vm_id>_<vm_name> — file name of the VM containing the id and name of the VM. For example, for a VM with id 12 and the name of test-vm, the file name should be 12_test_vm
If QEMU Guest Agent is running, you will get a response as shown below:
Fragment of response in JSON
```
{"return":{"version":"2.12.0","supported_commands":[{"enabled":true,"name":"guest-get-osinfo","success-response":true}
```
If QEMU Guest Agent is not running or is stopped, you will get a response as shown below:
```
error: Guest agent is not responding: QEMU guest agent is not connected
```
For VMs with CentOS OS, define the status of the guest-exec function:
```
virsh qemu-agent-command <vm_id>_<vm_name> '{"execute":"guest-info"}' --pretty | grep -B1 "guest-exec"
```
Comments to the command
<vm_id>_<vm_name> — file name of the VM containing the id and name of the VM. For example, for a VM with id 12 and the name of test-vm, the file name should be 12_test_vm
Fragment of the response, if the function is enabled
```
"enabled": true,
"name": "guest-exec",
```
Fragment of the response, if the function is disabled
```
"enabled": false,
"name": "guest-exec",
```

Diagnostics on the platform

To find the problem with QEMU Guest Agent, you can:

when creating a VM and reinstalling the OS, monitor the log of VM operations:
```
docker exec vm_box tail -f /var/log/host.log
```
when attempting to install or restore QEMU Guest Agent on a VM, monitor the log of QEMU Guest Agent operations:
```
docker exec vm_box tail -f /var/log/host_guest_agent.log
```

Restoring work

If QEMU Guest Agent is not installed

Connect to the VM via SSH.

Install QEMU Guest Agent:

CentOS

yum install qemu-guest-agent

Debian, Ubuntu

apt install qemu-guest-agent

Add QEMU Guest Agent to the autostart:
```
systemctl enable --now qemu-guest-agent
```
Check the status of QEMU Guest Agent:
```
systemctl status qemu-guest-agent
```
Check the status of the SELinux service:
```
sestatus
```
If the status is different from disable:
1. Disable SELinux. Replace the below line in the /etc/selinux/config file
```
SELINUX=enforcing
```
  with
```
SELINUX=disabled
```
2. Reboot the VM.

The file /etc/sysconfig/qemu-ga contains a line the below format

BLACKLIST_RPC=guest-file-open,guest-file-close,guest-file-read,guest-file-write,guest-file-seek,guest-file-flush,guest-exec,guest-exec-status

Mark this line as comment or delete it.
Restart QEMU Guest Agent:
```
systemctl restart qemu-guest-agent
```

If QEMU Guest Agent is stopped

Connect to the VM via SSH.
Start QEMU Guest Agent:
```
systemctl start qemu-guest-agent
```

If guest-exec function is disabled

Connect to the VM via SSH.

Run the command:

sed -i '/BLACKLIST_RPC=/cBLACKLIST_RPC=' /etc/sysconfig/qemu-ga

Restart QEMU Guest Agent:
```
systemctl restart qemu-guest-agent
```

Running QEMU Guest Agent on Windows

Installation

To prepare the VM for Virtio driver installation, create a 1 GB disk with Virtio connection type and connect it to the VM: Virtual machines section → select VM → Parameters button → Virtual disk → Connect one more disk → Create and connect a disk → select Size 1 GB and virtio Connection type → Connect the disk button.
Download and install the Virtio drivers.
- For Windows Server 2012 R2 use virtio-win-guest-tools v.0.1.189.
- For Windows Server 2008 use virtio-win-guest-tools v.0.1.137.
Download and install QEMU Guest Agent.

Diagnostics

Run the services.msc service manager and check that QEMU Guest Agent is in the list of running services. If the service is stopped, start it. If the service is not listed, install the QEMU Guest Agent software.

Example of QEMU Guest Agent status display in the manager