How to use the command 'systemd-detect-virt' (with examples)

The systemd-detect-virt command is a utility that is part of the systemd suite of tools. It is designed to detect whether a Linux system is running in a virtualized environment and, if so, what type of virtualization technology is being used. This can be particularly useful for system administrators who need to tailor configurations or optimizations based on whether a system is running on physical hardware, within a virtual machine, or in a container.

Use case 1: List detectable virtualization technologies

Code:

systemd-detect-virt --list

Motivation:

Understanding which virtualization technologies can be detected provides an administrator with insights into what systemd-detect-virt is capable of distinguishing. This is especially important when dealing with diverse environments where different virtualization solutions might be deployed.

Explanation:

• --list: This argument instructs systemd-detect-virt to output all the virtualization environments it is capable of detecting. It does not detect any current virtualization but shows a predefined list that the tool can recognize.

Example output:

kvm
qemu
zvm
vmware
xen
bochs
uml
parallels
bhyve
openvz
lxc
lxc-libvirt
systemd-nspawn
docker
rkt

Use case 2: Detect if running in a VM or container

Code:

systemd-detect-virt

Motivation:

Running this command without any additional arguments provides a straightforward way to check whether the system is running in a VM or container environment. This can be crucial for applying different configurations automatically or logging system information for auditing or troubleshooting.

Explanation:

Running systemd-detect-virt without arguments checks the system’s environment. It prints the detected virtualization technology’s name and returns a zero status code if virtualization is detected, or an empty string and a non-zero status code if running on physical hardware.

Example output:

qemu

Use case 3: Silently check for virtualization

Code:

systemd-detect-virt --quiet

Motivation:

In scripting scenarios, especially when automation is required, it might be necessary to check for virtualization without outputting any information to the console. This helps in focusing on the logic of a script without cluttering the output and allows scripts to act based on exit codes rather than displayed messages.

Explanation:

• --quiet: This flag suppresses standard output. The command will not print any messages or results; instead, it only returns an exit status code: zero if a virtual environment is detected and a non-zero code otherwise.

Example output:

(no output)

Use case 4: Detect container virtualization only

Code:

systemd-detect-virt --container

Motivation:

In environments that leverage both VM and container technologies, administrators may need precise detection between these two. This command helps identify if the system is running specifically inside a container, thus providing more granularity for configuration or deployment scripts.

Explanation:

• --container: This option makes systemd-detect-virt check exclusively for container-based virtualization solutions. If the system is inside a container, it outputs the container’s technology name and returns a zero exit status.

Example output:

docker

Use case 5: Detect hardware virtualization only

Code:

systemd-detect-virt --vm

Motivation:

Conversely, if you are only interested in detecting hardware-based virtualization solutions and wish to ignore container environments, this command provides that capability. It helps discern setups that rely on VM solutions for isolated environments, distinct from containers.

Explanation:

• --vm: This filter restricts the detection to virtual machine hypervisors, ignoring container virtualization technologies. It prints the hypervisor name if one is detected, otherwise it returns a non-zero status code if not.

Example output:

kvm

Conclusion:

The systemd-detect-virt command is a versatile tool for determining the virtualization context of a Linux system. This can aid in configuring systems appropriately for their environment, streamline automation scripts, and enhance understanding of the deployed infrastructure. Each use case allows administrators to fine-tune their detection based on specific environments, whether it’s for VMs, containers, or both.