A. Use the terraform destroy command. This command is used to remove all the resources that were created using the Terraform configuration1. It is the opposite of the terraform apply command, which is used to create resources. The terraform destroy command will first show a plan of what resources will be destroyed, and then ask for confirmation before proceeding. The command will also update the state file to reflect the changes. D. The administrator must manually delete the Linux server. This is because the Linux server was not deployed using Terraform, but using AWS Marketplace2. Therefore, Terraform does not have any information about the Linux server in its state file, and cannot manage or destroy it. The administrator will have to use the AWS console or CLI to delete the Linux server manually.

The other options are incorrect because:

There is no terraform validate command. The correct command is terraform plan, which is used to show a plan of what changes will be made by applying the configuration3. However, this command does not delete any resources, it only shows what will happen if terraform apply or terraform destroy is run.

There is no terraform destroy all command. The correct command is terraform destroy, which will destroy all the resources in the current configuration by default1. There is no need to add an all argument to the command.