How to Use the Command 'qm showcmd' (with Examples)

The qm showcmd command is a powerful utility within the Proxmox Virtual Environment (PVE) for administrators. It provides detailed insights and debug information on how a specific Virtual Machine (VM) is started. This is particularly useful when troubleshooting or fine-tuning your virtual machines to ensure optimal performance. The command essentially displays the exact command-line arguments passed when a VM is launched, offering transparency into the underlying processes of the VM.

Use Case 1: Show Command-Line for a Specific Virtual Machine

Code:

qm showcmd 101

Motivation:

When working with multiple virtual machines, understanding how each VM is configured to run can be critical. You may need to verify or audit the specific startup configurations for compliance, efficiency, or troubleshooting purposes. This command is especially advantageous when you need to compare different configurations or when you face unexpected behaviors from a particular VM, helping you pinpoint issues or confirm settings.

Explanation:

• qm refers to the QEMU Virtual Machine management tool in Proxmox.
• showcmd is the sub-command used to print the full command-line used to launch the specified VM.
• 101 represents the ID of the Virtual Machine whose startup command-line you wish to inspect. This ID must match the VM ID assigned within Proxmox.

Example Output:

/usr/bin/kvm -id 101 -name myVM -m 2048 -smp 2 -drive file=/var/lib/vz/images/101/vm-101-disk-0.qcow2,format=qcow2 -net user

This output showcases the command-line arguments used when starting the VM with ID 101, detailing the memory allocation, CPU count, and disk image path, among others.

Use Case 2: Put Each Option on a New Line to Enhance Human Readability

Code:

qm showcmd --pretty true 102

Motivation:

For system administrators and developers who prefer cleaner and more legible configurations, displaying each option on a new line can significantly enhance readability. This format helps in quickly identifying and understanding each parameter without the need for sorting through a potentially cluttered single-line display. It is particularly useful for documentation purposes or when presenting configurations to colleagues who might not be familiar with complex command-line outputs.

Explanation:

• qm and showcmd maintain their previous roles.
• --pretty true is an additional option to format each command-line argument on a new line for enhanced readability.
• 102 is the VM ID for which you want to generate the prettified command-line output.

Example Output:

/usr/bin/kvm
-id 102
-name myVM2
-m 4096
-smp 4
-drive file=/var/lib/vz/images/102/vm-102-disk-0.qcow2,format=qcow2
-net user

This format presents the information in an organized and easy-to-read fashion, making it much simpler to digest the configuration details.

Use Case 3: Fetch Configuration Values from a Specific Snapshot

Code:

qm showcmd --snapshot snapshot1 103

Motivation:

Snapshots are indispensable for managing changes in VMs, as they allow you to save the state of a VM at a particular point in time. When you wish to review or restore specific configurations from a snapshot, this use case becomes pivotal. It enables administrators to view the VM’s start-up command-line arguments as they were at the point the snapshot was taken, which can be crucial for debugging or restoring previous setup configurations.

Explanation:

• qm and showcmd function as described previously.
• --snapshot snapshot1 specifies that the command should fetch the command-line arguments from the named snapshot, snapshot1, which contains the VM’s configuration settings saved at that time.
• 103 is the ID of the VM whose snapshot configuration you wish to inspect.

Example Output:

/usr/bin/kvm -id 103 -name myVM3_snapshot1 -m 3072 -smp 2 -drive file=/var/lib/vz/images/103/vm-103-disk-snapshot1.qcow2,format=qcow2 -net user

This output provides insights into how your VM was configured when the snapshot was taken, enabling effective management of VM states and configurations over time.

Conclusion:

The qm showcmd command provides critical insights into the Virtual Machine’s startup parameters within Proxmox. By leveraging its different functionalities, system administrators can better manage, troubleshoot, and document their virtual environments. Whether you’re looking to verify current VM configurations, enhance readability of the argument list, or explore historic settings from snapshots, qm showcmd offers invaluable capabilities to streamline virtualization tasks.