Package Management Basics

Most modern Unix-like operating systems offer a centralized mechanism for finding and installing software. Software is usually distributed in the form of packages, kept in repositories. Working with packages is known as package management. Packages provide the basic components of an operating system, along with shared libraries, applications, services, and documentation.

A package management system does much more than one-time installation of software. It also provides tools for upgrading already-installed packages. Package repositories help to ensure that code has been vetted for use on your system, and that the installed versions of software have been approved by developers and package maintainers.

When configuring servers or development environments, it’s often necessary look beyond official repositories. Packages in the stable release of a distribution may be out of date, especially where new or rapidly-changing software is concerned. Nevertheless, package management is a vital skill for system administrators and developers, and the wealth of packaged software for major distributions is a tremendous resource.

This guide covers Debian, Ubuntu, CentOS, Fedora, SuSE, and FreeBSD and will require one of those distributions to be installed.

In a Windows environment, programs are packaged in .exe or .msi installers which will then install most of the files needed to run the program. If your computer doesn’t have some dependant applications, then the program that you are trying to run will either not install or not run properly. You will then have to scour the internet in order to find the missing required applications or libraries. For example in CentOS 7, in order to install the VIM text editor, I need to add the following packages:

 gpm-libs                    x86_64      1.20.7-5.el7           base       32 k
 groff-base                  x86_64      1.22.2-8.el7           base      942 k
 perl                        x86_64      4:5.16.3-286.el7       base      8.0 M
 perl-Carp                   noarch      1.26-244.el7           base       19 k
 perl-Encode                 x86_64      2.51-7.el7             base      1.5 M
 perl-Exporter               noarch      5.68-3.el7             base       28 k
 perl-File-Path              noarch      2.09-2.el7             base       26 k
 perl-File-Temp              noarch      0.23.01-3.el7          base       56 k
 perl-Filter                 x86_64      1.49-3.el7             base       76 k
 perl-Getopt-Long            noarch      2.40-2.el7             base       56 k
 perl-HTTP-Tiny              noarch      0.033-3.el7            base       38 k
 perl-PathTools              x86_64      3.40-5.el7             base       82 k
 perl-Pod-Escapes            noarch      1:1.04-286.el7         base       50 k
 perl-Pod-Perldoc            noarch      3.20-4.el7             base       87 k
 perl-Pod-Simple             noarch      1:3.28-4.el7           base      216 k
 perl-Pod-Usage              noarch      1.63-3.el7             base       27 k
 perl-Scalar-List-Utils      x86_64      1.27-248.el7           base       36 k
 perl-Socket                 x86_64      2.010-3.el7            base       49 k
 perl-Storable               x86_64      2.45-3.el7             base       77 k
 perl-Text-ParseWords        noarch      3.29-4.el7             base       14 k
 perl-Time-HiRes             x86_64      4:1.9725-3.el7         base       45 k
 perl-Time-Local             noarch      1.2300-2.el7           base       24 k
 perl-constant               noarch      1.27-2.el7             base       19 k
 perl-libs                   x86_64      4:5.16.3-286.el7       base      687 k
 perl-macros                 x86_64      4:5.16.3-286.el7       base       43 k
 perl-parent                 noarch      1:0.225-244.el7        base       12 k
 perl-podlators              noarch      2.5.1-3.el7            base      112 k
 perl-threads                x86_64      1.87-4.el7             base       49 k
 perl-threads-shared         x86_64      1.43-6.el7             base       39 k
 vim-common                  x86_64      2:7.4.160-1.el7        base      5.9 M
 vim-filesystem              x86_64      2:7.4.160-1.el7        base      9.6 k
 which                       x86_64      2.20-7.el7             base       41 k

Imagine trying to manually install all of these programs one at a time just to be able to install a text editor! In the early days of Linux, we faced these kinds of problems, however this problem is fixed with package management systems such as apt, yum, and others. Package managers simplify everything. They look at the package that you want to install such as VIM, LibreOffice, etc., then look at what other package it depends upon, the dependencies of those packages, and so on; then it downloads them all and installs them. For example, in order to install VIM in CentOS 7 today, I simply have to run yum install vim.

Most distributions offer a graphical or menu-driven front end to package collections. These can be a good way to browse by category and discover new software. Often, however, the quickest and most effective way to locate a package is to search with command-line tools.

When deciding what to install, it’s often helpful to read detailed descriptions of packages. Along with human-readable text, these often include metadata like version numbers and a list of the package’s dependencies.

Once you know the name of a package, you can usually install it and its dependencies with a single command. In general, you can supply multiple packages to install simply by listing them all.

Sometimes, even though software isn’t officially packaged for a given operating system, a developer or vendor will offer package files for download. You can usually retrieve these with your web browser, or viacurl on the command line. Once a package is on the target system, it can often be installed with a single command.

On Debian-derived systems, dpkg handles individual package files. If a package has unmet dependencies, gdebi can often be used to retrieve them from official repositories.

On CentOS and Fedora systems, yum and dnf are used to install individual files, and will also handle needed dependencies.

Since a package manager knows what files are provided by a given package, it can usually remove them cleanly from a system if the software is no longer needed.

In addition to web-based documentation, keep in mind that Unix manual pages (usually referred to as man pages) are available for most commands from the shell. To read a page, use the man command. For example, man yum will give you a brief manual on how to use yum.