You can start a DB2 instance from the GUI. You must know the password of the instance owner. The steps to restart a DB2 database instance are the same.
To start a DB2 instance
Access the DB2 Start Instance wizard.
Enter the instance name and home directory. Verify your UNIX user name and enter your password. The UNIX user name is the same as the instance name.
At the confirmation prompt, click Yes to confirm that you want to start the database.
If the DB2 instance starts successfully, you will receive a confirmation message. Click OK to continue.