what is apt in linux

apt in linux is an installation package management tool. It is a client/server system. If we want to use apt to install software, we can execute [sudo apt-get install packagename].

apt introduction

Advanced Packaging Tool (apt) is an installation package management under Linux tool.

Initially there are only .tar.gz packaging files, and the user must compile each software he wants to run on GNU/Linux. Users generally believe that it is necessary for the system to provide a method to manage these software packages installed on the machine. When Debian was born, such a management tool came into being, and it was named dpkg.

Thus the famous "package" concept first appeared in the GNU/Linux system, and later Red Hat decided to develop its own "rpm" package management system.

Soon a new problem stumped GNU/Linux producers. They needed a fast, practical and efficient way to install software packages. When the software package is updated, this tool should be able to automatically manage associated files. and maintain existing configuration files.

Debian once again took the lead in solving this problem, and APT (Advanced Packaging Tool) was born as the front end of dpkg. APT was later modified by Conectiva to manage rpm, and was adopted by other Linux distributions as their package management tools.

APT consists of several programs whose names begin with "apt-". apt-get, apt-cache, and apt-cdrom are command-line tools for handling software packages.

Linux command-apt is also the backend of other user front-end programs, such as dselect and aptitude.

As part of the operation, APT uses a file to list the mirror site addresses where software packages are available. This file is /etc/apt/sources.list.

How it works

APT is a client/server system. First copy all DEB packages on the server (DEB is the file extension of Debian software package format), then use APT's analysis tool (genbasedir) to analyze all DEB packages based on the header information of each DEB package, and The analysis results are recorded in a file, which is called the DEB index list. The DEB index list of the APT server is placed in the base folder.

Once the DEB in the APT server changes, be sure to use genbasedir to generate a new DEB index list. When installing or upgrading, the client must first query the DEB index list, so that all software packages with dependencies can be learned and downloaded to the client together for installation.

When the client needs to install, upgrade or delete a software package, after the client computer obtains the DEB index list compressed file, it will decompress it and place it in /var/state/apt/lists/, and When the client uses the apt-get install or apt-get upgrade command, the data in this folder will be compared with the DEB database in the client computer to know which DEBs are installed, not installed, or can be upgraded.

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