Azure Linux VM Agent overview

The Microsoft Azure Linux VM Agent (waagent) manages Linux and FreeBSD provisioning, along with virtual machine (VM) interaction with the Azure fabric controller. In addition to the Linux agent providing provisioning functionality, Azure provides the option of using cloud-init for some Linux operating systems.

The Linux agent provides the following functionality for Linux and FreeBSD Azure Virtual Machines deployments. For more information, see the Azure Linux VM Agent readme on GitHub.

Image provisioning

• Creates a user account
• Configures SSH authentication types
• Deploys SSH public keys and key pairs
• Sets the host name
• Publishes the host name to the platform DNS
• Reports the SSH host key fingerprint to the platform
• Manages the resource disk
• Formats and mounts the resource disk
• Configures swap space

Networking

• Manages routes to improve compatibility with platform DHCP servers
• Ensures the stability of the network interface name

Kernel

• Configures virtual NUMA (disabled for kernel 2.6.37)
• Consumes Hyper-V entropy for /dev/random
• Configures SCSI timeouts for the root device, which can be remote

Diagnostics

• Provides console redirection to the serial port

System Center Virtual Machine Manager deployments

• Detects and bootstraps the Virtual Machine Manager agent for Linux when it's running in a System Center Virtual Machine Manager 2012 R2 environment

VM Extension

• Injects components authored by Microsoft and partners into Linux VMs to enable software and configuration automation

You can find a VM Extension reference implementation on GitHub.

Communication

Information flow from the platform to the agent occurs through two channels:

• A boot-time attached DVD for VM deployments. This DVD includes an Open Virtualization Format (OVF)-compliant configuration file that contains all provisioning information other than the SSH key pairs.
• A TCP endpoint that exposes a REST API that's used to get deployment and topology configuration.

Requirements

Testing has confirmed that the following systems work with the Azure Linux VM Agent.

Distribution	x64	ARM64
Alma Linux	9.x+	9.x+
Debian	10+	11.x+
Azure Linux	2.x	2.x
openSUSE	12.3+	Not supported
Rocky Linux	9.x+	9.x+
SLES	12.x+, 15.x+	15.x SP4+
Ubuntu (LTS releases)	18.04+, 20.04+, 22.04+, 24.04+	20.04+, 22.04+, 24.04+

Other supported systems:

• The Agent works on more systems than those listed in the documentation. However, we do not test or provide support for distros that are not on the endorsed list. In particular, FreeBSD is not endorsed. The customer can try FreeBSD 8 and if they run into problems they can open an issue in our GitHub repository and we may be able to help.

The Linux agent depends on these system packages to function properly:

• Python 2.6+
• OpenSSL 1.0+
• OpenSSH 5.3+
• File system utilities: sfdisk, fdisk, mkfs, parted
• Password tools: chpasswd, sudo
• Text processing tools: sed, grep
• Network tools: ip-route
• Kernel support for mounting UDF file systems

Ensure that your VM has access to IP address 168.63.129.16. For more information, see What is IP address 168.63.129.16?.

Installation

The supported method of installing and upgrading the Azure Linux VM Agent uses an RPM or a DEB package from your distribution's package repository. All the endorsed distribution providers integrate the Azure Linux VM Agent package into their images and repositories. Some Linux distributions might disable the Azure Linux VM Agent Auto Update feature and some of the repositories might also contain older versions, those might have issues with modern extensions so, we recommend to have the latest stable version installed. To make sure the Azure Linux VM Agent is updating properly we recommend having the option AutoUpdate.Enabled=Y in the /etc/waagent.conf file or simply commenting out that option will result in its defaults too. Having AutoUpdate.Enabled=N will not allow the Azure Linux VM Agent to update properly.

For advanced installation options, such as installing from a source or to custom locations or prefixes, see Microsoft Azure Linux VM Agent. Other than these scenarios, we do not support or recommend upgrading or reinstalling the Azure Linux VM Agent from source.

Command-line options

Flags

• verbose: Increases verbosity of the specified command.
• force: Skips interactive confirmation for some commands.

Commands

• help: Lists the supported commands and flags.

• deprovision: Attempts to clean the system and make it suitable for reprovisioning. The operation deletes:

  • All SSH host keys, if Provisioning.RegenerateSshHostKeyPair is y in the configuration file.
  • Nameserver configuration in /etc/resolv.conf.
  • The root password from /etc/shadow, if Provisioning.DeleteRootPassword is y in the configuration file.
  • Cached DHCP client leases.

  The client resets the host name to localhost.localdomain.

  Warning

  Deprovisioning doesn't guarantee that the image is cleared of all sensitive information and suitable for redistribution.

• deprovision+user: Performs everything in deprovision and deletes the last provisioned user account (obtained from /var/lib/waagent) and associated data. Use this parameter when you deprovision an image that was previously provisioned on Azure so that it can be captured and reused.

• version: Displays the version of waagent.

• serialconsole: Configures GRUB to mark ttyS0, the first serial port, as the boot console. This option ensures that kernel boot logs are sent to the serial port and made available for debugging.

• daemon: Runs waagent as a daemon to manage interaction with the platform. This argument is specified to waagent in the waagent init script.

• start: Runs waagent as a background process.

Configuration

The /etc/waagent.conf configuration file controls the actions of waagent. Here's an example of a configuration file:

Provisioning.Enabled=y
Provisioning.DeleteRootPassword=n
Provisioning.RegenerateSshHostKeyPair=y
Provisioning.SshHostKeyPairType=rsa
Provisioning.MonitorHostName=y
Provisioning.DecodeCustomData=n
Provisioning.ExecuteCustomData=n
Provisioning.AllowResetSysUser=n
Provisioning.PasswordCryptId=6
Provisioning.PasswordCryptSaltLength=10
ResourceDisk.Format=y
ResourceDisk.Filesystem=ext4
ResourceDisk.MountPoint=/mnt/resource
ResourceDisk.MountOptions=None
ResourceDisk.EnableSwap=n
ResourceDisk.SwapSizeMB=0
LBProbeResponder=y
Logs.Verbose=n
OS.RootDeviceScsiTimeout=300
OS.OpensslPath=None
HttpProxy.Host=None
HttpProxy.Port=None
AutoUpdate.Enabled=y

Configuration options are of three types: Boolean, String, or Integer. You can specify the Boolean configuration options as y or n. The special keyword None might be used for some string type configuration entries.

Provisioning.Enabled

Type: Boolean
Default: y

This option allows the user to enable or disable the provisioning functionality in the agent. Valid values are y and n. If provisioning is disabled, SSH host and user keys in the image are preserved and configuration in the Azure provisioning API is ignored.

Provisioning.DeleteRootPassword

Type: Boolean
Default: n

If the value is y, the agent erases the root password in the /etc/shadow file during the provisioning process.

Provisioning.RegenerateSshHostKeyPair

Type: Boolean
Default: y

If the value is y, the agent deletes all SSH host key pairs from /etc/ssh/ during the provisioning process, including ECDSA, DSA, and RSA. The agent generates a single fresh key pair.

Configure the encryption type for the fresh key pair by using the Provisioning.SshHostKeyPairType entry. Some distributions re-create SSH key pairs for any missing encryption types when the SSH daemon is restarted--for example, after a reboot.

Provisioning.SshHostKeyPairType

Type: String
Default: rsa

You can set this option to an encryption algorithm type that the SSH daemon supports on the VM. The typically supported values are rsa, dsa, and ecdsa. The putty.exe file on Windows doesn't support ecdsa. If you intend to use putty.exe on Windows to connect to a Linux deployment, use rsa or dsa.

Provisioning.MonitorHostName

Type: Boolean
Default: y

If the value is y, waagent monitors the Linux VM for a host name change, as returned by the hostname command. Waagent then automatically updates the networking configuration in the image to reflect the change. To push the name change to the DNS servers, networking restarts on the VM. This restart results in brief loss of internet connectivity.

Provisioning.DecodeCustomData

Type: Boolean
Default: n

If the value is y, waagent decodes CustomData from Base64.

Provisioning.ExecuteCustomData

Type: Boolean
Default: n

If the value is y, waagent runs CustomData after provisioning.

Provisioning.AllowResetSysUser

Type: Boolean
Default: n

This option allows the password for the system user to be reset. It's disabled by default.

Provisioning.PasswordCryptId

Type: String
Default: 6

This option specifies the algorithm that crypt uses when it's generating a password hash. Valid values are:

• 1: MD5
• 2a: Blowfish
• 5: SHA-256
• 6: SHA-512

Provisioning.PasswordCryptSaltLength

Type: String
Default: 10

This option specifies the length of random salt used in generating a password hash.

ResourceDisk.Format

Type: Boolean
Default: y

If the value is y, waagent formats and mounts the resource disk that the platform provides, unless the file system type that the user requested in ResourceDisk.Filesystem is ntfs. The agent makes a single Linux partition (ID 83) available on the disk. This partition isn't formatted if it can be successfully mounted.

ResourceDisk.Filesystem

Type: String
Default: ext4

This option specifies the file system type for the resource disk. Supported values vary by Linux distribution. If the string is X, then mkfs.X should be present on the Linux image.

ResourceDisk.MountPoint

Type: String
Default: /mnt/resource

This option specifies the path at which the resource disk is mounted. The resource disk is a temporary disk and might be emptied when the VM is deprovisioned.

ResourceDisk.MountOptions

Type: String
Default: None

This option specifies disk mount options to be passed to the mount -o command. The value is a comma-separated list of values, for example, nodev,nosuid. For more information, see the mount(8) manual page.

ResourceDisk.EnableSwap

Type: Boolean
Default: n

If you set this option, the agent creates a swap file (/swapfile) on the resource disk and adds it to the system swap space.

ResourceDisk.SwapSizeMB

Type: Integer
Default: 0

This option specifies the size of the swap file in megabytes.

Logs.Verbose

Type: Boolean
Default: n

If you set this option, log verbosity is boosted. Waagent logs to /var/log/waagent.log and uses the system logrotate functionality to rotate logs.

OS.EnableRDMA

Type: Boolean
Default: n

If you set this option, the agent attempts to install and then load an RDMA kernel driver that matches the version of the firmware on the underlying hardware.

OS.RootDeviceScsiTimeout

Type: Integer
Default: 300

This option configures the SCSI timeout in seconds on the OS disk and data drives. If it's not set, the system defaults are used.

OS.OpensslPath

Type: String
Default: None

You can use this option to specify an alternate path for the openssl binary to use for cryptographic operations.

HttpProxy.Host, HttpProxy.Port

Type: String
Default: None

If you set this option, the agent uses this proxy server to access the internet.

AutoUpdate.Enabled

Type: Boolean
Default: y

Enable or disable autoupdate for goal state processing. The default value is y.

Automatic log collection in the Azure Linux Guest Agent

As of version 2.7+, the Azure Linux Guest Agent has a feature to automatically collect some logs and upload them. This feature currently requires systemd. It uses a new systemd slice called azure-walinuxagent-logcollector.slice to manage resources while it performs the collection.

The purpose is to facilitate offline analysis. The agent produces a .zip file of some diagnostics logs before uploading them to the VM's host. Engineering teams and support professionals can retrieve the file to investigate issues for the VM owner. For technical information on the files that the Azure Linux Guest Agent collects, see the azurelinuxagent/common/logcollector_manifests.py file in the agent's GitHub repository.

You can disable this option by editing /etc/waagent.conf. Update Logs.Collect to n.

Ubuntu Cloud Images

Ubuntu Cloud Images use cloud-init to do many configuration tasks that the Azure Linux VM Agent would otherwise manage. The following differences apply:

• Provisioning.Enabled defaults to n on Ubuntu Cloud Images that use cloud-init to perform provisioning tasks.

• The following configuration parameters have no effect on Ubuntu Cloud Images that use cloud-init to manage the resource disk and swap space:

  • ResourceDisk.Format
  • ResourceDisk.Filesystem
  • ResourceDisk.MountPoint
  • ResourceDisk.EnableSwap
  • ResourceDisk.SwapSizeMB

To configure the resource disk mount point and swap space on Ubuntu Cloud Images during provisioning, see the following resources:

• Ubuntu wiki: AzureSwapPartitions
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