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Manage Azure Linux VMs

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To optimize the manageability of Azure Linux VMs, you must understand the interaction between the Azure platform and the VM operating system (OS). This interaction is especially significant during VM provisioning.

Platform-supported management agents

VM provisioning is the process of creating Azure VM configuration parameter values, such as hostname, username, and password, that are available to the OS during the startup or boot process. A provisioning agent consumes these values, configures the OS, and reports the results when finished.

Azure supports cloud-init provisioning agents and Azure Linux Agent (WALA).

• Cloud-init provisioning agents are a widely used approach to customizing Linux during an initial boot. You can use cloud-init to install packages and write files, or to configure users and security. Because cloud-init is called during the initial boot process, you don't need any more steps or required agents to apply the configuration. For more information, see the Cloud-init documentation.

  Note

  Microsoft is enhancing the VM configuration process to use cloud-init instead of the Linux Agent. Existing cloud-init customers can use their current cloud-init scripts, and new customers can use rich cloud-init configuration functionality.

• WALA. WALA is an Azure platform-specific agent you can use to provision and configure Azure VMs. You can also use WALA to implement support for Azure extensions.

Boot diagnostics and serial console

To optimize managing and troubleshooting the boot process, you can enable boot diagnostics and use the serial console.

Enable boot diagnostics

Boot diagnostics help you analyze boot failures by collecting serial log information and screenshots. You can enable boot diagnostics during or after VM creation. To expedite the provisioning process, select the managed storage account option to store the boot diagnostics data.

Use the Azure VM serial console

You can use Azure VM serial console access for troubleshooting boot failures. Serial console provides a text-based console over the Linux VM's ttyS0 serial port. This access is independent of network connectivity or OS state.

Azure users with at least Contributor-level permissions can access the serial console by using the Azure portal or Azure CLI. You must enable boot diagnostics to use the serial console.

The serial console can help you restore a VM to an operational state in situations like the following scenarios:

• Broken file system table fstab files

• Misconfigured firewall rules

• File system corruption

• SSH configuration issues

• Common bootloader issues:

  • GRUB menu countdown on Gen2 Azure VMs. Because legacy hardware has been removed from emulation in Generation 2 Azure VMs, the Grand Unified Bootloader (GRUB) menu countdown timer can count down too quickly to display real-time loading of the default entry. To address this issue, replace the default entry "timeout=5" with "timeout=100000" in /boot/grub/grub.conf, or /etc/default/grub, or their equivalents.

  • Kernel panic boot error in kdump. If the crash dump capture ends with a kernel panic on boot, you should reserve more memory for the kernel. For example, in the Ubuntu GRUB configuration, change the parameter crashkernel=384M-:128M to crashkernel=384M-:256M.

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