Detailed and comprehensive introduction to configuring Ubuntu’s apt sources.
APT, which stands for Advanced Package Tool, is a package management tool in the Ubuntu operating system. It is used to install, upgrade, and remove software packages from software repositories. The configuration file for APT is located at /etc/apt/sources.list, where you can specify the sources of software packages, known as APT sources.
APT sources are servers where software packages are stored, categorized into official and third-party sources. Official sources are maintained by Ubuntu and offer a wide range of software packages for users to install. Third-party sources, on the other hand, are maintained by other organizations or individuals and provide additional software packages.
Here is an example of a typical APT source configuration file:
deb http://archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
Each line in the above configuration file represents an APT repository, with the following format:
deb [源地址] [发行版名称] [软件包分类]
Among them, [source address] specifies the source of the software package, [distribution name] specifies the corresponding Ubuntu distribution of the software package, and [package category] specifies the category of the software package (such as main, restricted, universe, multiverse, etc.).
In the above example, the first line specifies the address of the official source, including major software package categories such as main (containing most free software packages), restricted (containing some restricted software packages), universe (containing open-source software packages), and multiverse (containing some restricted open-source software packages).
The second, third, and fourth lines respectively designate the official update source, backup source, and security source. The update source provides updated software packages, the backup source provides test packages before official release, and the security source provides security fixes.
In addition to official sources, users also have the option to add third-party sources. To do so, they can add the source address to the configuration file, and then run the apt-get update command to update the source list. For example, if there is a third-party source called ppa:example/ppa, it can be added in the following way:
deb http://ppa.launchpad.net/example/ppa/ubuntu focal main
Once added, run the command apt-get update to update the source list, and then you can use apt-get install to install the software packages provided by the third-party source.
In summary, configuring APT sources is done by editing the /etc/apt/sources.list file to specify the sources of software packages, which can include official sources and third-party sources. Each line in the configuration file represents an APT source, including the source address, distribution name, and package category. To add a third-party source, the source address needs to be added to the configuration file and the apt-get update command needs to be run to update the source list.
