Use cloud-init to run a bash script in a Linux VM in Azure

Applies to: ✔️ Linux VMs ✔️ Flexible scale sets

This article shows you how to use cloud-init to run an existing bash script on a Linux virtual machine (VM) or virtual machine scale sets (VMSS) at provisioning time in Azure. These cloud-init scripts run on first boot once the resources have been provisioned by Azure. For more information about how cloud-init works natively in Azure and the supported Linux distros, see cloud-init overview

Run a bash script with cloud-init

With cloud-init you do not need to convert your existing scripts into a cloud-config, cloud-init accepts multiple input types, one of which is a bash script.

If you have been using the Linux Custom Script Azure Extension to run your scripts, you can migrate them to use cloud-init. However, Azure Extensions have integrated reporting to alert to script failures, a cloud-init image deployment will NOT fail if the script fails.

To see this functionality in action, create a simple bash script for testing. Like the cloud-init #cloud-config file, this script must be local to where you will be running the AzureCLI commands to provision your virtual machine. For this example, create the file in the Cloud Shell not on your local machine. You can use any editor you wish. Enter sensible-editor simple_bash.sh to create the file and see a list of available editors. Choose #1 to use the nano editor. Make sure that the whole cloud-init file is copied correctly, especially the first line.

#!/bin/sh
echo "this has been written via cloud-init" + $(date) >> /tmp/myScript.txt

Before deploying this image, you need to create a resource group with the az group create command. An Azure resource group is a logical container into which Azure resources are deployed and managed. The following example creates a resource group named myResourceGroup in the eastus location.

az group create --name myResourceGroup --location eastus

Now, create a VM with az vm create and specify the bash script file with --custom-data simple_bash.sh as follows:

az vm create \
  --resource-group myResourceGroup \
  --name centos74 \
  --image OpenLogic:CentOS:7-CI:latest \
  --custom-data simple_bash.sh \
  --generate-ssh-keys 

Verify bash script has run

SSH to the public IP address of your VM shown in the output from the preceding command. Enter your own publicIpAddress as follows:

ssh <publicIpAddress>

Change to the /tmp directory and verify that myScript.txt file exists and has the appropriate text inside of it. If it does not, you can check the /var/log/cloud-init.log for more details. Search for the following entry:

Running config-scripts-user using lock Running command ['/var/lib/cloud/instance/scripts/part-001']

Next steps

For additional cloud-init examples of configuration changes, see the following: