As part of your DB2® installation procedure, you can create an initial instance of the database manager. The default name is DB2_01 in Version 9.5 or later releases.
On Linux and UNIX, the initial instance can be called anything you want within the naming rules guidelines. The instance name is used to set up the directory structure.
Before using the database manager, the database environment for each user must be updated so that it can access an instance and run the DB2 database programs. This applies to all users (including administrative users).
On Linux and UNIX operating systems, sample script files are provided to help you set the database environment. The files are: db2profile for Bourne or Korn shell, and db2cshrc for C shell. These scripts are located in the sqllib subdirectory under the home directory of the instance owner. The instance owner or any user belonging to the instance's SYSADM group can customize the script for all users of an instance. Use sqllib/userprofile and sqllib/usercshrc to customize a script for each user.
The blank files sqllib/userprofile and sqllib/usercshrc are created during instance creation to allow you to add your own instance environment settings. The db2profile and db2cshrc files are overwritten during an instance update in a DB2 fix pack installation. If you do not want the new environment settings in the db2profile or db2cshrc scripts, you can override them using the corresponding user script, which is called at the end of the db2profile or db2cshrc script. During an instance upgrade (using the db2iupgrade command), the user scripts are copied over so that your environment modifications will still be in use.