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Configuring Custom Data (Linux CVM)

Last updated: 2022-09-01 17:36:39

    Overview

    When creating a CVM instance, you can configure an instance by specifying custom data. During the first launch of the CVM, the custom data will be passed into the CVM in text format and be executed. If you purchase multiple CVM instances at a time, the custom data text will be executed on all CVM instances during their first launch.

    This document describes how to transfer a shell script when a CVM instance for Linux is started for the first time.

    Notes

    • Linux operating systems that support custom data include:
      • 64-bit OSs: CentOS 6.8 and later, Ubuntu Server 14.04.1 LTS and later, and openSUSE 42.3 x86
      • 32-bit OSs: CentOS 6.8 and later
    • A command can be executed by passing text only when a CVM instance is launched for the first time.
    • The text to be transferred must be Base64-encoded. Perform encoding in a Linux environment to avoid format incompatibility.
    • Execute the user input as root. Therefore, the sudo command is not required in the script. The root user can access all the files you created. If you need to grant other users with the access permission, modify the permission in the script.
    • During launch, executing specified tasks in custom data will increase the amount of time it takes to launch the CVM. We recommend that you wait for a few minutes, and after the tasks are completed, test whether the tasks have been successfully executed.
    • In this sample, the shell script must start with #! and the path directing to the interpreter of the script to be read (generally starting with /bin/bash).

    Directions

    Writing a shell script

    1. Run the following command to create a shell script named "script_text.sh".

      vi script_text.sh
      
    2. Press i to switch to the editing mode, refer to the following content, write it into the file, and save the "script_text.sh" script.

      #!/bin/bash
      echo "Hello Tencent Cloud."
      
    Note

    The shell script must start with #! and the path directing to the interpreter of the script to be read (generally starting with /bin/bash). For more information on the shell script, see BASH Programming - Introduction HOW-TO.

    Base64-encoding the script file

    1. Run the following command to Base64-encode the "script_text.sh" script.
      # Base64-encode the script
      base64 script_text.sh
      
      

    The following information is returned:

    # Result returned after the encoding
    IyEvYmluL2Jhc2gKZWNobyAiSGVsbG8gVGVuY2VudCBDbG91ZC4iCg==
    
    1. Run the following command to verify the result returned after the script is Base64-encoded.
      # Base64-decode the returned result to verify the command
      echo "IyEvYmluL2Jhc2gKZWNobyAiSGVsbG8gVGVuY2VudCBDbG91ZC4iCg==" | base64 -d
      

    Passing text

    We provide multiple methods to launch an instance, and here we introduce two of them. Choose a method according to your requirements:

    1. Purchase an instance as instructed in Creating Instances via CVM Purchase Page and click Advanced Settings in "2. Complete configuration".
    2. In the text box in Advanced Settings, enter the encoded result returned in the Base64-encoded script.
      For example, the encoded result of the script_text script with Base64 is IyEvYmluL2Jhc2gKZWNobyAiSGVsbG8gVGVuY2VudCBDbG91ZC4iCg==.
    3. Follow the prompts on the interface to complete CVM creation.
      Note

      CVM will run the script through the open-source software cloud-init. For more information on cloud-init, visit the cloud-init website.

    Viewing execution logs

    After the CVM instance is created successfully, you can run the following command to view the script execution log:

    cat /var/log/cloud-init-output.log
    
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