How to run a command on startup for ubuntu server 18.04?

I want to run a command when I then start an EC2 instance. The AMI of the instance is Ubuntu Server 18.04 LTS (HVM), SSD Volume Type.

The following are the methods I've tried:

1. Create a script named test.sh under /etc/init.d/.

2. sudo chmod +x /etc/init.d/test.sh

3. sudo chown root.root /etc/init.d/test.sh

4. sudo update-rc.d test.sh defaults

5. Stop the EC2 instance.

6. Start the EC2 instance.

Here's the content of test.sh:

#!/bin/bashecho hello > /home/ubuntu/test.log

I expected that I will see test.log file under /home/ubuntu. But I couldn't find the file.

I've also tried adding echo hello > /home/ubuntu/test.log to /etc/rc.local file. But it doesn't work, eighter.

Another method I've tried is Adding echo hello > /home/ubuntu/test.log to user data. This doesn't work, either.

I found a line saying 2019-05-13 03:23:18,162 - __init__.py[WARNING]: Unhandled non-multipart (text/x-not-multipart) userdata: 'b'echo hello > /home/ubunt'...' in /var/log/cloud-init.log. But this is just a warning, not an error message.

What might be wrong with my configuration?

Are there any error logs left on the EC2?