To check if database or listener is running on Linux, you could check if Oracle processes are running, for example ps aux | grep pmon(or grep lsnr for listener).
Pmon is process monitor, process responsible for "housekeeping", like freeing buffer cache or some resources that are not in use anymore. It is always running if the instance is up ( but this process does not guarantee that you can connect, because the database could be started in mount mode, anyway it is a start of a troubleshooting ).
It seems that you didn't set ORACLE_SID, ORACLE_BASE, ORACLE_HOME and PATH variables. On link that you provided, environment variables are set at the runtime. You could permanently set them in your .bashrc or bash_profile file.
Add these lines to your .bashrc file(it is in your users home directory, for example /home/oracle/.bashrc).
ORACLE_SID=name_of_your_database
ORACLE_BASE=/oracle/base/
ORACLE_HOME=/oracle/base/dbhome_1
PATH=$PATH:$HOME/bin:$ORACLE_HOME/bin
export ORACLE_SID ORACLE_BASE ORACLE_HOME PATH
Reload new bash profile with command - source .bashrc and try again and read Oracle installation documentation for more detalis.
However, since Ubuntu is not supported OS for Oracle, there is no way to know for sure what the problem really is or was. If installation is for learning purpose, easier for you will be to install some supported OS in a VirtualBox for example, or to use Oracle prebuild VMs.
Best Answer
Yes, you can do that by running the runinstaller passing the silent argument. Also, it is possible to save and use response files, which basically contain standard configurations and parameters for the software installation. It's very useful if you will need to perform installations following a specific standard on a frequent basis.
Here's the docs: https://docs.oracle.com/database/121/LADBI/app_nonint.htm
Another option: You don't need to have "GUI" installed, you can emulate the Graphical Interface. There are plenty of tools. tigervnc is a great one. To install it, run as sudo: yum install tigervnc and after installation is completed, start it by running vncserver. You will be prompted for the user's password. Then you can issue: ps -ef | grep vnc, which will show you details about the program execution, being the port the most important. Now you can externally gain access to the server through VNC Viewer (needs to be installed), by specifying server's ip and port/ display #. Note: Yum if your OS support it. Otherwise, use rpm (problem is every dependency will need to be separately installed).
Hope it helps.