类 Unix 系统 Package Management 基础知识

Package Management Basics: apt, yum, dnf, pkg

Introduction

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 Packages in the stable release of a distribution may be out of date, especially where new or rapidly-changing software is concerned.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 is intended as a quick reference for the fundamentals of finding, installing, and upgrading packages on a variety of distributions, and should help you translate that knowledge between systems.

 

Package Management Systems: A Brief Overview

Most package systems are built around collections of package files. A package file is usually an archive which contains compiled binaries and other resources making up the software, along with installation scripts. Packages also contain valuable metadata, including their dependencies, a list of other packages required to install and run them.

While their functionality and benefits are broadly similar, packaging formats and tools vary by platform:

Operating System	Format	Tool(s)
Debian	.deb	apt, apt-cache, apt-get, dpkg
Ubuntu	.deb	apt, apt-cache, apt-get, dpkg
CentOS	.rpm	yum
Fedora	.rpm	dnf
FreeBSD	Ports, .txz	make, pkg

In Debian and systems based on it, like Ubuntu, Linux Mint, and Raspbian, the package format is the .deb file. APT, the Advanced Packaging Tool, provides commands used for most common operations: Searching repositories, installing collections of packages and their dependencies, and managing upgrades. APT commands operate as a front-end to the lower-level dpkg utility, which handles the installation of individual .deb files on the local system, and is sometimes invoked directly.

Recent releases of most Debian-derived distributions include the apt command, which offers a concise and unified interface to common operations that have traditionally been handled by the more-specific apt-get and apt-cache. Its use is optional, but may simplify some tasks.

CentOS, Fedora, and other members of the Red Hat family use RPM files. In CentOS, yum is used to interact with both individual package files and repositories.

In recent versions of Fedora, yum has been supplanted by dnf, a modernized fork which retains most of yum’s interface.

FreeBSD’s binary package system is administered with the pkg command. FreeBSD also offers the Ports Collection, a local directory structure and tools which allow the user to fetch, compile, and install packages directly from source using Makefiles. It’s usually much more convenient to use pkg, but occasionally a pre-compiled package is unavailable, or you may need to change compile-time options.

 

Update Package Lists

Most systems keep a local database of the packages available from remote repositories. It’s best to update this database before installing or upgrading packages. As a partial exception to this pattern, yum and dnf will check for updates before performing some operations, but you can ask them at any time whether updates are available.

System	Command
Debian / Ubuntu	sudo apt-get update
	sudo apt update
CentOS	yum check-update
Fedora	dnf check-update
FreeBSD Packages	sudo pkg update
FreeBSD Ports	sudo portsnap fetch update

 

Upgrade Installed Packages

Making sure that all of the installed software on a machine stays up to date would be an enormous undertaking without a package system. You would have to track upstream changes and security alerts for hundreds of different packages. While a package manager doesn’t solve every problem you’ll encounter when upgrading software, it does enable you to maintain most system components with a few commands.

On FreeBSD, upgrading installed ports can introduce breaking changes or require manual configuration steps. It’s best to read /usr/ports/UPDATING before upgrading with portmaster.

System	Command	Notes
Debian / Ubuntu	sudo apt-get upgrade	Only upgrades installed packages, where possible.
	sudo apt-get dist-upgrade	May add or remove packages to satisfy new dependencies.
	sudo apt upgrade	Like apt-get upgrade.
	sudo apt full-upgrade	Like apt-get dist-upgrade.
CentOS	sudo yum update
Fedora	sudo dnf upgrade
FreeBSD Packages	sudo pkg upgrade
FreeBSD Ports	less /usr/ports/UPDATING	Uses less to view update notes for ports (use arrow keys to scroll, press q to quit).
	cd /usr/ports/ports-mgmt/portmaster && sudo make install && sudo portmaster -a	Installs portmaster and uses it to update installed ports.

 

Find a Package

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.

System	Command	Notes
Debian / Ubuntu	apt-cache search search_string
	apt search search_string
CentOS	yum search search_string
	yum search all search_string	Searches all fields, including description.
Fedora	dnf search search_string
	dnf search all search_string	Searches all fields, including description.
FreeBSD Packages	pkg search search_string	Searches by name.
	pkg search -f search_string	Searches by name, returning full descriptions.
	pkg search -D search_string	Searches description.
FreeBSD Ports	cd /usr/ports && make search name=package	Searches by name.
	cd /usr/ports && make search key=search_string	Searches comments, descriptions, and dependencies.

 

View Info About a Specific Package

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.

System	Command	Notes
Debian / Ubuntu	apt-cache show package	Shows locally-cached info about a package.
	apt show package
	dpkg -s package	Shows the current installed status of a package.
CentOS	yum info package
	yum deplist package	Lists dependencies for a package.
Fedora	dnf info package
	dnf repoquery --requires package	Lists dependencies for a package.
FreeBSD Packages	pkg info package	Shows info for an installed package.
FreeBSD Ports	cd /usr/ports/category/port && cat pkg-descr

 

Install a Package from Repositories

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.

System	Command	Notes
Debian / Ubuntu	sudo apt-get install package
	sudo apt-get install package1 package2 ...	Installs all listed packages.
	sudo apt-get install -y package	Assumes “yes” where apt would usually prompt to continue.
	sudo apt install package	Displays a colored progress bar.
CentOS	sudo yum install package
	sudo yum install package1 package2 ...	Installs all listed packages.
	sudo yum install -y package	Assumes “yes” where yum would usually prompt to continue.
Fedora	sudo dnf install package
	sudo dnf install package1 package2 ...	Installs all listed packages.
	sudo dnf install -y package	Assumes “yes” where dnf would usually prompt to continue.
FreeBSD Packages	sudo pkg install package
	sudo pkg install package1 package2 ...	Installs all listed packages.
FreeBSD Ports	cd /usr/ports/category/port && sudo make install	Builds and installs a port from source.

 

Install a Package from the Local Filesystem

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 via curl 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.

System	Command	Notes
Debian / Ubuntu	sudo dpkg -i package.deb
	sudo apt-get install -y gdebi && sudo gdebi package.deb	Installs and uses gdebi to install package.deb and retrieve any missing dependencies.
CentOS	sudo yum install package.rpm
Fedora	sudo dnf install package.rpm
FreeBSD Packages	sudo pkg add package.txz
	sudo pkg add -f package.txz	Installs package even if already installed.

 

Remove One or More Installed Packages

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.

System	Command	Notes
Debian / Ubuntu	sudo apt-get remove package
	sudo apt remove package
	sudo apt-get autoremove	Removes unneeded packages.
CentOS	sudo yum remove package
Fedora	sudo dnf erase package
FreeBSD Packages	sudo pkg delete package
	sudo pkg autoremove	Removes unneeded packages.
FreeBSD Ports	sudo pkg delete package
	cd /usr/ports/path_to_port && make deinstall	De-installs an installed port.

 

The apt Command

Administrators of Debian-family distributions are generally familiar with apt-get and apt-cache. Less widely known is the simplified apt interface, designed specifically for interactive use.

Traditional Command	apt Equivalent
apt-get update	apt update
apt-get dist-upgrade	apt full-upgrade
apt-cache search string	apt search string
apt-get install package	apt install package
apt-get remove package	apt remove package
apt-get purge package	apt purge package

While apt is often a quicker shorthand for a given operation, it’s not intended as a complete replacement for the traditional tools, and its interface may change between versions to improve usability. If you are using package management commands inside a script or a shell pipeline, it’s a good idea to stick with apt-get and apt-cache.

 

Get Help

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 man:

• man page

In man, you can navigate with the arrow keys. Press / to search for text within the page, and q to quit.

System	Command	Notes
Debian / Ubuntu	man apt-get	Updating the local package database and working with packages.
	man apt-cache	Querying the local package database.
	man dpkg	Working with individual package files and querying installed packages.
	man apt	Working with a more concise, user-friendly interface to most basic operations.
CentOS	man yum
Fedora	man dnf
FreeBSD Packages	man pkg	Working with pre-compiled binary packages.
FreeBSD Ports	man ports	Working with the Ports Collection.

 

Conclusion and Further Reading

This guide provides an overview of basic operations that can be cross-referenced between systems, but only scratches the surface of a complex topic. For greater detail on a given system, you can consult the following resources:

• This guide covers Ubuntu and Debian package management in detail.
• There’s an official CentOS guide to managing software with yum.
• There’s a Fedora wiki page about dnf, and an official manual for dnf itself.
• This guide covers FreeBSD package management using pkg.
• The FreeBSD Handbook contains a section on using the Ports Collection.