Hi @Luphina, thank you for reaching out.
Here are some of my initial observations
- According to our docs we support Ubuntu 14.04 and Ubuntu 16.04: https://docs.mattermost.com/install/requirements.html#mattermost-server-operating-system.
- Here are our docs on how to install each https://docs.mattermost.com/install/install-ubuntu-1404.html and https://docs.mattermost.com/install/install-ubuntu-1604.html.
Would you be able to try the installation with one of these versions?