Run commands when you launch an EC2 instance with user data input

When you launch an Amazon EC2 instance, you can pass user data to the instance that is used to perform automated configuration tasks, or to run scripts after the instance starts.

If you're interested in more complex automation scenarios, you might consider AWS CloudFormation. For more information, see Deploying applications on Amazon EC2 with AWS CloudFormation in the AWS CloudFormation User Guide.

On Linux instances, you can pass two types of user data to Amazon EC2: shell scripts and cloud-init directives. You can also pass this data into the launch instance wizard as plain text, as a file (this is useful for launching instances with the command line tools), or as base64-encoded text (for API calls).

On Windows instances, the launch agents handle your user data scripts. The following sections cover the differences in how user data is handled on each operating system.

User data in the AWS Management Console

You can specify instance user data when you launch the instance. If the root volume of the instance is an EBS volume, you can also stop the instance and update its user data.

Specify instance user data at launch with the Launch Wizard

You can specify user data when you launch an instance with the Launch Wizard in the EC2 console. To specify user data on launch, follow the procedure for launching an instance. The User data field is located in the Advanced details section of the launch instance wizard. Enter your PowerShell script in the User data field, and then complete the instance launch procedure.

In the following screenshot of the User data field, the example script creates a file in the Windows temporary folder, using the current date and time in the file name. When you include <persist>true</persist>, the script is run every time you reboot or start the instance. If you leave the User data has already been base64 encoded checkbox empty, the Amazon EC2 console performs the base64 encoding for you.

For more information, see Specify instance user data at launch with the Launch Wizard. For a Linux example that uses the AWS CLI, see User data and the AWS CLI. For a Windows example that uses the Tools for Windows PowerShell, see User data and the Tools for Windows PowerShell.

View and update the instance user data

You can view the instance user data for any instance, and you can update the instance user data for a stopped instance.

How Amazon EC2 handles user data for Linux instances

In the following examples, the commands from the Install a LAMP server on Amazon Linux 2 are converted to a shell script and a set of cloud-init directives that run when the instance launches. In each example, the following tasks are performed by the user data:

Prerequisites

The examples in this topic assume the following:

User data and shell scripts

If you are familiar with shell scripting, this is the easiest and most complete way to send instructions to an instance at launch. Adding these tasks at boot time adds to the amount of time it takes to boot the instance. You should allow a few minutes of extra time for the tasks to complete before you test that the user script has finished successfully.

User data shell scripts must start with the #! characters and the path to the interpreter you want to read the script (commonly /bin/bash). For an introduction on shell scripting, see the Bash Reference Manual on the GNU Operating System website.

Scripts entered as user data are run as the root user, so do not use the sudo command in the script. Remember that any files you create will be owned by the root user; if you need a non-root user to have file access, you should modify the permissions accordingly in the script. Also, because the script is not run interactively, you cannot include commands that require user feedback (such as yum update without the -y flag).

If you use an AWS API, including the AWS CLI, in a user data script, you must use an instance profile when launching the instance. An instance profile provides the appropriate AWS credentials required by the user data script to issue the API call. For more information, see Using instance profiles in the IAM User Guide. The permissions you assign to the IAM role depend on which services you are calling with the API. For more information, see IAM roles for Amazon EC2.

The cloud-init output log file captures console output so it is easy to debug your scripts following a launch if the instance does not behave the way you intended. To view the log file, connect to the instance and open /var/log/cloud-init-output.log.

When a user data script is processed, it is copied to and run from /var/lib/cloud/instances/instance-id/. The script is not deleted after it is run. Be sure to delete the user data scripts from /var/lib/cloud/instances/instance-id/ before you create an AMI from the instance. Otherwise, the script will exist in this directory on any instance launched from the AMI.

Update the instance user data

To update the instance user data, you must first stop the instance. If the instance is running, you can view the user data but you cannot modify it.

User data and cloud-init directives

The cloud-init package configures specific aspects of a new Amazon Linux instance when it is launched; most notably, it configures the .ssh/authorized_keys file for the ec2-user so you can log in with your own private key. For more information about the configuration tasks that the cloud-init package performs for Amazon Linux instances, see Using cloud-init on Amazon Linux 2 in the Amazon Linux 2 User Guide.

The cloud-init user directives can be passed to an instance at launch the same way that a script is passed, although the syntax is different. For more information about cloud-init, see http://cloudinit.readthedocs.org/en/latest/index.html.

Adding these tasks at boot time adds to the amount of time it takes to boot an instance. You should allow a few minutes of extra time for the tasks to complete before you test that your user data directives have completed.

User data and the AWS CLI

You can use the AWS CLI to specify, modify, and view the user data for your instance. For information about viewing user data from your instance using instance metadata, see Access instance metadata for an EC2 instance.

On Windows, you can use the AWS Tools for Windows PowerShell instead of using the AWS CLI. For more information, see User data and the Tools for Windows PowerShell .

Example: Specify user data at launch

To specify user data when you launch your instance, use the run-instances command with the --user-data parameter. With run-instances, the AWS CLI performs base64 encoding of the user data for you.

The following example shows how to specify a script as a string on the command line:

aws ec2 run-instances --image-id ami-abcd1234 --count 1 --instance-type m3.medium \
    --key-name my-key-pair --subnet-id subnet-abcd1234 --security-group-ids sg-abcd1234 \
    --user-data echo user data

The following example shows how to specify a script using a text file. Be sure to use the file:// prefix to specify the file.

aws ec2 run-instances --image-id ami-abcd1234 --count 1 --instance-type m3.medium \
    --key-name my-key-pair --subnet-id subnet-abcd1234 --security-group-ids sg-abcd1234 \
    --user-data file://my_script.txt

The following is an example text file with a shell script.

#!/bin/bash
yum update -y
service httpd start
chkconfig httpd on

Example: Modify the user data of a stopped instance

You can modify the user data of a stopped instance using the modify-instance-attribute command. With modify-instance-attribute, the AWS CLI does not perform base64 encoding of the user data for you.

Use the --attribute and --value parameters to use the encoded text file to specify the user data. Be sure to use the file:// prefix to specify the file.

aws ec2 modify-instance-attribute --instance-id i-1234567890abcdef0 --attribute userData --value file://my_script_base64.txt

Example: Clear the user data of a stopped instance

To delete the existing user data, use the modify-instance-attribute command as follows:

aws ec2 modify-instance-attribute --instance-id i-1234567890abcdef0 --user-data Value=

Example: View user data

To retrieve the user data for an instance, use the describe-instance-attribute command. With describe-instance-attribute, the AWS CLI does not perform base64 decoding of the user data for you.

aws ec2 describe-instance-attribute --instance-id i-1234567890abcdef0 --attribute userData

The following is example output with the user data base64 encoded.

{
    "UserData": {
        "Value": "IyEvYmluL2Jhc2gKeXVtIHVwZGF0ZSAteQpzZXJ2aWNlIGh0dHBkIHN0YXJ0CmNoa2NvbmZpZyBodHRwZCBvbg=="
    },
    "InstanceId": "i-1234567890abcdef0"
}

The following is example output.

#!/bin/bash
yum update -y
service httpd start
chkconfig httpd on

Combine shell scripts and cloud-init directives

By default, you can include only one content type in user data at a time. However, you can use the text/cloud-config and text/x-shellscript content-types in a mime-multi part file to include both a shell script and cloud-init directives in your user data.

The following shows the mime-multi part format.

Content-Type: multipart/mixed; boundary="//"
MIME-Version: 1.0
	
--//
Content-Type: text/cloud-config; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="cloud-config.txt"
	
#cloud-config
cloud-init directives
	
--//
Content-Type: text/x-shellscript; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="userdata.txt"
	
#!/bin/bash
shell script commands
--//--

For example, the following user data includes cloud-init directives and a bash shell script. The cloud-init directives creates a file (/test-cloudinit/cloud-init.txt), and writes Created by cloud-init to that file. The bash shell script creates a file (/test-userscript/userscript.txt) and writes Created by bash shell script to that file.

Content-Type: multipart/mixed; boundary="//"
MIME-Version: 1.0
	
--//
Content-Type: text/cloud-config; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="cloud-config.txt"
	
#cloud-config
runcmd:
- [ mkdir, /test-cloudinit ]
write_files:
- path: /test-cloudinit/cloud-init.txt
content: Created by cloud-init
	
--//
Content-Type: text/x-shellscript; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="userdata.txt"
	
#!/bin/bash
mkdir test-userscript
touch /test-userscript/userscript.txt
echo "Created by bash shell script" >> /test-userscript/userscript.txt
--//--

How Amazon EC2 handles user data for Windows instances

On Windows instances, the launch agent performs the tasks related to user data. For more information, see the following:

For examples of the assembly of a UserData property in a AWS CloudFormation template, see Base64 Encoded UserData Property and Base64 Encoded UserData Property with AccessKey and SecretKey.

For an example of running commands on an instance within an Auto Scaling group that works with lifecycle hooks, see Tutorial: Configure user data to retrieve the target lifecycle state through instance metadata in the Amazon EC2 Auto Scaling User Guide.

User data scripts

For EC2Config or EC2Launch to run scripts, you must enclose the script within a special tag when you add it to user data. The tag that you use depends on whether the commands run in a Command Prompt window (batch commands) or use Windows PowerShell.

If you specify both a batch script and a Windows PowerShell script, the batch script runs first and the Windows PowerShell script runs next, regardless of the order in which they appear in the instance user data.

If you use an AWS API, including the AWS CLI, in a user data script, you must use an instance profile when launching the instance. An instance profile provides the appropriate AWS credentials required by the user data script to make the API call. For more information, see Instance profiles. The permissions you assign to the IAM role depend on which services you are calling with the API. For more information, see IAM roles for Amazon EC2.

Syntax for batch scripts

Specify a batch script using the script tag. Separate the commands using line breaks as shown in the following example.

<script>
    echo Current date and time >> %SystemRoot%\Temp\test.log
    echo %DATE% %TIME% >> %SystemRoot%\Temp\test.log
</script>

By default, user data scripts run one time when you launch the instance. To run the user data scripts every time you reboot or start the instance, add <persist>true</persist> to the user data.

<script>
    echo Current date and time >> %SystemRoot%\Temp\test.log
    echo %DATE% %TIME% >> %SystemRoot%\Temp\test.log
</script>
<persist>true</persist>

EC2Launch v2 agent

To run an XML user data script as a detached process with the EC2Launch v2 executeScript task in the UserData stage, add <detach>true</detach> to the user data.

<script>
    echo Current date and time >> %SystemRoot%\Temp\test.log
    echo %DATE% %TIME% >> %SystemRoot%\Temp\test.log
</script>
<detach>true</detach>

Syntax for Windows PowerShell scripts

The AWS Windows AMIs include the AWS Tools for Windows PowerShell, so you can specify these cmdlets in user data. If you associate an IAM role with your instance, you don't need to specify credentials to the cmdlets, as applications that run on the instance use the role's credentials to access AWS resources (for example, Amazon S3 buckets).

Specify a Windows PowerShell script using the <powershell> tag. Separate the commands using line breaks. The <powershell> tag is case-sensitive.

For example:

<powershell>
    $file = $env:SystemRoot + "\Temp\" + (Get-Date).ToString("MM-dd-yy-hh-mm")
    New-Item $file -ItemType file
</powershell>

By default, the user data scripts run one time when you launch the instance. To run the user data scripts every time you reboot or start the instance, add <persist>true</persist> to the user data.

<powershell>
    $file = $env:SystemRoot + "\Temp\" + (Get-Date).ToString("MM-dd-yy-hh-mm")
    New-Item $file -ItemType file
</powershell>
<persist>true</persist>

You can specify one or more PowerShell arguments with the <powershellArguments> tag. If no arguments are passed, EC2Launch and EC2Launch v2 add the following argument by default: -ExecutionPolicy Unrestricted.

Example:

<powershell>
    $file = $env:SystemRoot + "\Temp" + (Get-Date).ToString("MM-dd-yy-hh-mm")
    New-Item $file -ItemType file
</powershell>
<powershellArguments>-ExecutionPolicy Unrestricted -NoProfile -NonInteractive</powershellArguments>

EC2Launch v2 agent

To run an XML user data script as a detached process with the EC2Launch v2 executeScript task in the UserData stage, add <detach>true</detach> to the user data.

<powershell>
    $file = $env:SystemRoot + "\Temp\" + (Get-Date).ToString("MM-dd-yy-hh-mm")
    New-Item $file -ItemType file
</powershell>
<detach>true</detach>

Syntax for YAML configuration scripts

If you are using EC2Launch v2 to run scripts, you can use the YAML format. To view configuration tasks, details, and examples for EC2Launch v2, see EC2Launch v2 task configuration.

Specify a YAML script with the executeScript task.

Example YAML syntax to run a PowerShell script

version: 1.0
    tasks:
    - task: executeScript
      inputs:
      - frequency: always
        type: powershell
        runAs: localSystem
        content: |-
          $file = $env:SystemRoot + "\Temp\" + (Get-Date).ToString("MM-dd-yy-hh-mm")
          New-Item $file -ItemType file

Example YAML syntax to run a batch script

version: 1.1
    tasks:
    - task: executeScript
      inputs:
      - frequency: always
        type: batch
        runAs: localSystem
        content: |-
          echo Current date and time >> %SystemRoot%\Temp\test.log
          echo %DATE% %TIME% >> %SystemRoot%\Temp\test.log

Base64 encoding

If you're using the Amazon EC2 API or a tool that does not perform base64 encoding of the user data, you must encode the user data yourself. If not, an error is logged about being unable to find script or powershell tags to run. The following is an example that encodes using Windows PowerShell.

$UserData = [System.Convert]::ToBase64String([System.Text.Encoding]::ASCII.GetBytes($Script))

The following is an example that decodes using PowerShell.

$Script = [System.Text.Encoding]::UTF8.GetString([System.Convert]::FromBase64String($UserData))

For more information about base64 encoding, see https://www.ietf.org/rfc/rfc4648.txt.

User data execution

By default, all AWS Windows AMIs have user data execution enabled for the initial launch. You can specify that user data scripts are run the next time the instance reboots or restarts. Alternatively, you can specify that user data scripts are run every time the instance reboots or restarts.

User data scripts are run from the local administrator account when a random password is generated. Otherwise, user data scripts are run from the System account.

Instance launch scripts

Scripts in the instance user data are run during the initial launch of the instance. If the persist tag is found, user data execution is enabled for subsequent reboots or starts. The log files for EC2Launch v2, EC2Launch, and EC2Config contain the output from the standard output and standard error streams.

EC2Launch v2

The log file for EC2Launch v2 is C:\ProgramData\Amazon\EC2Launch\log\agent.log.

The following information is logged when the user data is run:

EC2Launch

The log file for EC2Launch is C:\ProgramData\Amazon\EC2-Windows\Launch\Log\UserdataExecution.log.

The C:\ProgramData folder might be hidden. To view the folder, you must show hidden files and folders.

The following information is logged when the user data is run:

EC2Config

The log file for EC2Config is C:\Program Files\Amazon\Ec2ConfigService\Logs\Ec2Config.log. The following information is logged when the user data is run:

Run scripts during subsequent reboots or starts

When you update instance user data, user data scripts are not run automatically when you reboot or start the instance. However, you can enable user data execution so that user data scripts are run one time when you reboot or start the instance, or every time you reboot or start the instance.

If you choose the Shutdown with Sysprep option, user data scripts are run the next time the instance starts or reboots, even if you did not enable user data execution for subsequent reboots or starts. The user data scripts will not be executed on subsequent reboots or starts.

User data and the Tools for Windows PowerShell

You can use the Tools for Windows PowerShell to specify, modify, and view the user data for your instance. For information about viewing user data from your instance using instance metadata, see Access instance metadata for an EC2 instance. For information about user data and the AWS CLI, see User data and the AWS CLI.

Example: Specify instance user data at launch

Create a text file with the instance user data. To run user data scripts every time you reboot or start the instance, add <persist>true</persist>, as shown in the following example.

<powershell>
    $file = $env:SystemRoot + "\Temp\" + (Get-Date).ToString("MM-dd-yy-hh-mm")
    New-Item $file -ItemType file
</powershell>
<persist>true</persist>

To specify instance user data when you launch your instance, use the New-EC2Instance command. This command does not perform base64 encoding of the user data for you. Use the following commands to encode the user data in a text file named script.txt.

PS C:\> $Script = Get-Content -Raw script.txt
PS C:\> $UserData = [System.Convert]::ToBase64String([System.Text.Encoding]::ASCII.GetBytes($Script))

Use the -UserData parameter to pass the user data to the New-EC2Instance command.

PS C:\> New-EC2Instance -ImageId ami-abcd1234 -MinCount 1 -MaxCount 1 -InstanceType m3.medium \
    -KeyName my-key-pair -SubnetId subnet-12345678 -SecurityGroupIds sg-1a2b3c4d \
    -UserData $UserData

Example: Update instance user data for a stopped instance

You can modify the user data of a stopped instance using the Edit-EC2InstanceAttribute command.

Create a text file with the new script. Use the following commands to encode the user data in the text file named new-script.txt.

PS C:\> $NewScript = Get-Content -Raw new-script.txt
PS C:\> $NewUserData = [System.Convert]::ToBase64String([System.Text.Encoding]::ASCII.GetBytes($NewScript))

Use the -UserData and -Value parameters to specify the user data.

PS C:\> Edit-EC2InstanceAttribute -InstanceId i-1234567890abcdef0 -Attribute userData -Value $NewUserData

Example: View instance user data

To retrieve the user data for an instance, use the Get-EC2InstanceAttribute command.

PS C:\> (Get-EC2InstanceAttribute -InstanceId i-1234567890abcdef0 -Attribute userData).UserData

The following is example output. Note that the user data is encoded.

PHBvd2Vyc2hlbGw+DQpSZW5hbWUtQ29tcHV0ZXIgLU5ld05hbWUgdXNlci1kYXRhLXRlc3QNCjwvcG93ZXJzaGVsbD4=

Use the following commands to store the encoded user data in a variable and then decode it.

PS C:\> $UserData_encoded = (Get-EC2InstanceAttribute -InstanceId i-1234567890abcdef0 -Attribute userData).UserData
PS C:\> [System.Text.Encoding]::UTF8.GetString([System.Convert]::FromBase64String($UserData_encoded))

The following is example output.

<powershell>
    $file = $env:SystemRoot + "\Temp\" + (Get-Date).ToString("MM-dd-yy-hh-mm")
    New-Item $file -ItemType file
</powershell>
<persist>true</persist>

Example: Rename the instance to match the tag value

You can use the Get-EC2Tag command to read the tag value, rename the instance on first boot to match the tag value, and reboot. To run this command successfully, you must have a role with ec2:DescribeTags permissions attached to the instance because tag information is retrieved by the API call. For more information on settings permissions by using IAM roles, see Attach an IAM role to an instance.

IMDSv2

<powershell>
    [string]$token = Invoke-RestMethod -Headers @{"X-aws-ec2-metadata-token-ttl-seconds" = "21600"} -Method PUT -Uri 'http://169.254.169.254/latest/api/token' -UseBasicParsing
    $instanceId = Invoke-RestMethod -Headers @{"X-aws-ec2-metadata-token" = $token} -Method GET -Uri 'http://169.254.169.254/latest/meta-data/instance-id' -UseBasicParsing
	$nameValue = (Get-EC2Tag -Filter @{Name="resource-id";Value=$instanceid},@{Name="key";Value="Name"}).Value
	$pattern = "^(?![0-9]{1,15}$)[a-zA-Z0-9-]{1,15}$"
	#Verify Name Value satisfies best practices for Windows hostnames
	If ($nameValue -match $pattern) 
	    {Try
	        {Rename-Computer -NewName $nameValue -Restart -ErrorAction Stop} 
	    Catch
	        {$ErrorMessage = $_.Exception.Message
	        Write-Output "Rename failed: $ErrorMessage"}}
	Else
	    {Throw "Provided name not a valid hostname. Please ensure Name value is between 1 and 15 characters in length and contains only alphanumeric or hyphen characters"}
</powershell>

IMDSv1

<powershell>
	$instanceId = (Invoke-WebRequest http://169.254.169.254/latest/meta-data/instance-id -UseBasicParsing).content
	$nameValue = (Get-EC2Tag -Filter @{Name="resource-id";Value=$instanceid},@{Name="key";Value="Name"}).Value
	$pattern = "^(?![0-9]{1,15}$)[a-zA-Z0-9-]{1,15}$"
	#Verify Name Value satisfies best practices for Windows hostnames
	If ($nameValue -match $pattern) 
	    {Try
	        {Rename-Computer -NewName $nameValue -Restart -ErrorAction Stop} 
	    Catch
	        {$ErrorMessage = $_.Exception.Message
	        Write-Output "Rename failed: $ErrorMessage"}}
	Else
	    {Throw "Provided name not a valid hostname. Please ensure Name value is between 1 and 15 characters in length and contains only alphanumeric or hyphen characters"}
</powershell>

You can also rename the instance using tags in instance metadata, if your instance is configured to access tags from the instance metadata. For more information, see View tags for your EC2 instances using instance metadata.

IMDSv2

<powershell>
    [string]$token = Invoke-RestMethod -Headers @{"X-aws-ec2-metadata-token-ttl-seconds" = "21600"} -Method PUT -Uri 'http://169.254.169.254/latest/api/token' -UseBasicParsing
	$nameValue = Invoke-RestMethod -Headers @{"X-aws-ec2-metadata-token" = $token} -Method GET -Uri 'http://169.254.169.254/latest/meta-data/tags/instance/Name' -UseBasicParsing
	$pattern = "^(?![0-9]{1,15}$)[a-zA-Z0-9-]{1,15}$"
	#Verify Name Value satisfies best practices for Windows hostnames
	If ($nameValue -match $pattern) 
	    {Try
	        {Rename-Computer -NewName $nameValue -Restart -ErrorAction Stop} 
	    Catch
	        {$ErrorMessage = $_.Exception.Message
	        Write-Output "Rename failed: $ErrorMessage"}}
	Else
	    {Throw "Provided name not a valid hostname. Please ensure Name value is between 1 and 15 characters in length and contains only alphanumeric or hyphen characters"}
</powershell>

IMDSv1

<powershell>
	$nameValue = Get-EC2InstanceMetadata -Path /tags/instance/Name
	$pattern = "^(?![0-9]{1,15}$)[a-zA-Z0-9-]{1,15}$"
	#Verify Name Value satisfies best practices for Windows hostnames
	If ($nameValue -match $pattern) 
	    {Try
	        {Rename-Computer -NewName $nameValue -Restart -ErrorAction Stop} 
	    Catch
	        {$ErrorMessage = $_.Exception.Message
	        Write-Output "Rename failed: $ErrorMessage"}}
	Else
	    {Throw "Provided name not a valid hostname. Please ensure Name value is between 1 and 15 characters in length and contains only alphanumeric or hyphen characters"}
</powershell>