This information should be included with the "Installing the DB2 Control Center" chapter in your Quick Beginnings book.
After leaving the DB2 installer on Linux and returning to the terminal window, type the following commands to set the correct environment to run the DB2 Control Center:
su -l <instance name> export JAVA_HOME=/usr/jdk118 export DISPLAY=<your machine name>:0
Then, open another terminal window and type:
su root xhost +<your machine name>
Close that terminal window and return to the terminal where you are logged in as the instance owner ID, and type the command:
db2cc
to start the Control Center.