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 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
```

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
```

VMmanager 6: Administrator guide