Configuration of the Advanced Packaging Tool (APT) system repositories is stored in the /etc/apt/sources.list configuration file. An example of this file is referenced here, along with information on adding or removing repository references from the file.

Here is a simple example of a typical /etc/apt/sources.list file.

You may edit the file to enable repositories or disable them. For example, to disable the requirement of inserting the Ubuntu CD-ROM whenever package operations occur, simply comment out the appropriate line for the CD-ROM, which appears at the top of the file:

# no more prompting for CD-ROM please
# deb cdrom:[Ubuntu 8.04_Hardy_Heron - Release i386 (20070419.1)]/ hardy main restricted