User-defined scripts are a type of script provided by Alibaba Cloud to enable users to customize the startup behavior of ECS instances. For details, see User-defined data.

This example uses a Linux instance to demonstrate how to use a user-defined script to create a new account, with the root user privilege, when creating a Linux instance. User-defined scripts can also be used to create a new account with the administrator privilege for a Windows instance.

Scenarios

Use user-defined scripts of instances if you want to achieve the following results when creating a Linux ECS instance:

  • Disable the default root account that comes with a Linux ECS instance. You can use the script to customize how to disable the root user and how many root user privileges are disabled.
  • Create a new account with the root user privilege and customize the account name.
  • Use only SSH key pairs, but not user passwords, for remote logon to manage the instance by using the new account with the root user privilege.
  • If this new account is required to perform operations that can only be done by a user with root user privilege, the sudo command can be used without a password for privilege escalation.

Procedure

To create a new account with the root user privilege, follow these steps:

  1. Create a Linux instance. Configure the instance as follows:
    • Network Type: Select VPC.
    • Instance Type: Select an I/O-optimized instance.
    • Operating System: Select CentOS 7.2 in Public Image tab.
  2. Enter the following script in the User Data box on the instance creation page:
    #! /bin/sh
    useradd test
    echo "test   ALL=(ALL)        NOPASSWD:ALL" | tee -a /etc/sudoers
    mkdir /home/test/.ssh
    touch /home/test/.ssh/authorized_keys
    echo "ssh-rsa AAAAB3NzaC1yc2EAAAABJQAAAQEAhGqhEh/rGbIMCGItFVtYpsXPQrCaunGJKZVIWtINrGZwusLc290qDZ93KCeb8o6X1Iby1Wm+psZY8THE+/BsXq0M0HzfkQZD2vXuhRb4xi1z98JHskX+0jnbjqYGY+Brgai9BvKDXTTSyJtCYUnEKxvcK+d1ZwxbNuk2QZ0ryHESDbSaczlNFgFQEDxhCrvko+zWLjTVnomVUDhdMP2g6fZ0tgFVwkJFV0bE7oob3NOVcrx2TyhfcAjA4M2/Ry7U2MFADDC+EVkpoVDm0SOT/hYJgaVM1xMDlSeE7kzX7yZbJLR1XAWV1xzZkNclY5w1kPnW8qMYuSwhpXzt4gsF0w== rsa-key-20170217" | tee -a /home/test/.ssh/authorized_keys
    
    Note
    • The first line must be #!. /bin/sh,with no leading space.
    • Do not enter unnecessary spaces or carriage return characters in the text.
    • The last line is your public key. You can define it.
    • You can add other configuration in the script, as you need.
    • The example script only applies to CentOS 7.2. If you are using other images, customize the script according to the operating system types.
  3. Select post-creation settings in security settings.
  4. After you finish the configuration, click Buy Now and activate the instance by following instructions on the page.

After the instance is created, you can use the new test user to connect to the instance using an SSH private key. You can also escalate the permission level using the sudo command and run operations that require the root user privilege, as shown in the following figure.