Learn about Azure-VM-Utils

Applies to: ✔️ Linux VMs ✔️ Flexible scale sets

The azure-vm-utils package provides essential utilities and udev rules to optimize the Linux experience on Azure Virtual Machines. This package consolidates device management tools for Small Computer System Interface (SCSI), Non-Volatile Memory Express (NVMe), Microsoft Azure Network Adapter (MANA), and Mellanox devices, making disk identification and management more reliable and consistent across different VM configurations.

NVMe udev rules

Newer virtual machines (VMs) SKUs on Azure use the NVMe interface for disk management. VMs with NVMe interfaces interpret and present disks differently from VMs that use SCSI interfaces. For details, see SCSI to NVMe conversion.

NVMe udev rules in this package consolidate critical tools and udev rules to create stable, predictable symlinks for Azure disks. This package provides an easy and reliable way to identify disks, making automation, troubleshooting, and management simpler.

Symlinks

WALinuxAgent currently includes udev rules to provide several symlinks for SCSI disks:

• /dev/disk/azure/resource
• /dev/disk/azure/root
• /dev/disk/azure/scsi0/lun<lun>
• /dev/disk/azure/scsi1/lun<lun>

The rules found in WALinuxAgent are being extended with azure-vm-utils to add identification support for NVMe devices.

The following symlinks are provided for all instances with NVMe disks:

• /dev/disk/azure/data/by-lun/<lun>
• /dev/disk/azure/local/by-serial/<serial>
• /dev/disk/azure/os

For v6 and newer VM sizes with local NVMe disks that support namespace identifiers, the following links are also available:

• /dev/disk/azure/local/by-index/<index>
• /dev/disk/azure/local/by-name/<name>

SCSI compatibility

To ensure backward compatibility for disks using SCSI controllers, azure-vm-utils supports the following links:

• /dev/disk/azure/os
• /dev/disk/azure/resource

Linux distribution support

The following distros and versions currently include az-vm-utils in their default images:

Installation

If the package isn't present in the default platform image, install it via package managers or from the GitHub repository.

Manual installation

For distributions where azure-vm-utils isn't preinstalled, build and install it manually:

# Clone the repository
git clone https://github.com/Azure/azure-vm-utils.git
cd azure-vm-utils

# Build the package
cmake .
make

# Install (requires root privileges)
sudo make install

Utilities

azure-nvme-id

The azure-nvme-id utility helps identify Azure NVMe devices and their properties. This utility is useful for troubleshooting and scripting.

To run the utility:

sudo azure-nvme-id

To run in udev mode (typically used by udev rules):

DEVNAME=/dev/nvme0n1 azure-nvme-id --udev

Using the symlinks

After azure-vm-utils is installed, you can use the predictable symlinks for disk operations instead of relying on device names that might change between reboots.

Examples

List all Azure disk symlinks:

find /dev/disk/azure/ -type l

Access the OS disk:

ls -la /dev/disk/azure/os

Access data disks by LUN:

ls -la /dev/disk/azure/data/by-lun/

Access local NVMe disks by serial number:

ls -la /dev/disk/azure/local/by-serial/

Verification

To verify that azure-vm-utils is working correctly on your VM:

1. Check if the package is installed:

   # For RPM-based systems
   rpm -qa azure-vm-utils
   
   # For DEB-based systems
   dpkg -l azure-vm-utils
   

2. Verify udev rules are in place:

   ls -al /usr/lib/udev/rules.d/10-azure-unmanaged-sriov.rules
   ls -al /usr/lib/udev/rules.d/80-azure-disk.rules
   

3. Check for Azure disk symlinks:

   find /dev/disk/azure -type l