Analyze the functions and characteristics of apt, yum, dnf and pkg

Introduction

Most modern Unix-like operating systems provide a centralized mechanism for searching and installing software. Software is usually stored in repositories and distributed through packages. The work of handling packages is called package management. Packages provide the basic components of an operating system, as well as shared libraries, applications, services, and documentation.

introduce

In addition to installing software, the package management system also provides tools to update installed packages. Package repositories help ensure that the code used in your system has been reviewed and that the installed version of the software has been approved by developers and package maintainers.

When configuring a server or development environment, it is best to understand the situation of packages outside the official repository. Packages in a distribution's stable version may be out of date, especially for new or rapidly evolving software. However, package management is a vital skill for both system administrators and developers, and packaged software is a huge asset to major Linux distributions.

This guide is designed to quickly introduce the basics of finding, installing, and upgrading packages on various Linux distributions, and to help you cross-reference these contents across multiple systems.

Package Management System: A Brief Overview

Most package systems are built around collections of package files. A package file is typically an archive file that contains compiled binaries and other resources for the software, as well as installation scripts. Package files also contain valuable metadata, including their dependencies and a list of other packages required to install and run them.

While the functionality and benefits of these package management systems are largely the same, packaging formats and tools vary by platform:

operating system	Format	tool
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

Debian and its derivatives, such as Ubuntu, Linux Mint and Raspbian, their package format is .deb. APT This advanced package management tool provides commands for the most common operations: search repositories, install packages and their dependencies, and manage upgrades. In the local system, we can also use the dpkg program to install a single deb file. The APT command serves as the front end of the underlying dpkg, and sometimes it is also called directly.

Most recently released debian derivatives include the apt command, which provides a concise and unified interface for common operations usually handled by apt-get and apt-cache commands. This command is optional, but using it can simplify some tasks.

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

In recent Fedora versions, yum has been replaced by dnf, which is a modern branch of it that retains most of yum's interfaces.

FreeBSD’s binary package system is managed by the pkg command. FreeBSD also provides the Ports collection, which is a local directory structure and tool that allows users to use Makefile to compile and install packages directly from the source code after obtaining the source code.

Update package list

Most systems will have a local package database corresponding to the remote repository. It is best to update this database before installing or upgrading packages. In addition, yum and dnf will also automatically check for updates before performing some operations. Of course you can update the system at any time.

system	Order
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

Update installed packages

Without a package system, it is a difficult task to ensure that all installed software on the machine is kept up to date. You will have to track upstream changes and security alerts for hundreds of different packages. While a package manager doesn't solve every problem you encounter when upgrading software, it does enable you to use some commands to maintain most system components.

On FreeBSD, upgrading installed ports may introduce breaking changes, and some steps require manual configuration, so it is best to read the contents of /usr/ports/UPDATING before updating via portmaster.

system	Order	illustrate
Debian / Ubuntu	sudo apt-get upgrade	Only update installed packages
	sudo apt-get dist-upgrade	Packages may be added or removed to satisfy new dependencies
	sudo apt upgrade	Similar to apt-get upgrade
	sudo apt full-upgrade	Similar to apt-get dist-upgrade
CentOS	sudo yum update
Fedora	sudo dnf upgrade
FreeBSD Packages	sudo pkg upgrade
FreeBSD Ports	less /usr/ports/UPDATING	Use less to view the update prompts of ports (use the up and down cursor keys to scroll and press q to exit).
	cd /usr/ports/ports-mgmt/portmaster && sudo make install && sudo portmaster -a	Install portmaster and then use it to update installed ports

Search for a package

Most distributions provide graphical or menu-driven tools for package collections. We can browse software by category, which is also a good way to discover new software. However, the fastest and most efficient way to find a package is to search using a command line tool.

system	Order	illustrate
Debian / Ubuntu	apt-cache search search_string
	apt search search_string
CentOS	yum search search_string
	yum search all search_string	Search all fields, including description
Fedora	dnf search search_string
	dnf search all search_string	Search all fields, including description
FreeBSD Packages	pkg search search_string	Search by name
	pkg search -f search_string	Search by name and return full description
	pkg search -D search_string	Search description
FreeBSD Ports	cd /usr/ports && make search name=package	Search by name
	cd /usr/ports && make search key=search_string	Search comments, descriptions and dependencies

View information about a software package

Before installing a software package, we can get a lot of useful information by carefully reading the package description. In addition to human-readable text, these typically include metadata like version numbers and a list of the package's dependencies.

system	Order	illustrate
Debian / Ubuntu	apt-cache show package	Display local cache information about packages
	apt show package
	dpkg -s package	Display the current installation status of the package
CentOS	yum info package
	yum deplist package	List package dependencies
Fedora	dnf info package
	dnf repoquery --requires package	List package dependencies
FreeBSD Packages	pkg info package	Display information about installed packages
FreeBSD Ports	cd /usr/ports/category/port && cat pkg-descr

Install package from repository

After knowing the package name, you can usually install it and its dependencies with one command. You can also install multiple packages at once, just list them all.

system	Order	illustrate
Debian / Ubuntu	sudo apt-get install package
	sudo apt-get install package1 package2 ...	Install all listed packages
	sudo apt-get install -y package	Where apt prompts whether to continue, the default is yes
	sudo apt install package	Display a colored progress bar
CentOS	sudo yum install package
	sudo yum install package1 package2 ...	Install all listed packages
	sudo yum install -y package	When yum prompts whether to continue, it will directly default to yes
Fedora	sudo dnf install package
	sudo dnf install package1 package2 ...	Install all listed packages
	sudo dnf install -y package	Where dnf prompts whether to continue, the default is yes
FreeBSD Packages	sudo pkg install package
	sudo pkg install package1 package2 ...	Install all listed packages
FreeBSD Ports	cd /usr/ports/category/port && sudo make install	Build and install a port from source

Install a package from the local file system

For a given operating system, sometimes some software does not officially provide the corresponding package, then the developer or supplier will need to provide the download of the package file. You can usually retrieve these packages through a web browser, or retrieve this information through the command line curl. After downloading the package to the target system, we can usually install it with a single command.

On Debian-derived systems, dpkg is used to process individual package files. If a package has unmet dependencies, then we can use gdebi to retrieve them from the official repository.

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

system	Order	illustrate
Debian / Ubuntu	sudo dpkg -i package.deb
	sudo apt-get install -y gdebi && sudo gdebi package.deb	Install gdebi, then use gdebi to install package.deb and handle 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	Even installed packages will be reinstalled

Remove one or more installed packages

Because the package manager knows what files are provided by a given package, it can often cleanly remove those files from the system if a piece of software is no longer needed.

system	Order	illustrate
Debian / Ubuntu	sudo apt-get remove package
	sudo apt remove package
	sudo apt-get autoremove	Delete unnecessary packages
CentOS	sudo yum remove package
Fedora	sudo dnf erase package
FreeBSD Packages	sudo pkg delete package
	sudo pkg autoremove	Delete unnecessary packages
FreeBSD Ports	sudo pkg delete package
	cd /usr/ports/path_to_port && make deinstall	Uninstall port

apt command

Admins of Debian family distributions are usually familiar with apt-get and apt-cache. Less well known is the simplified apt interface, which is designed for interactive use.

Traditional commands	Equivalent apt command
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

Although apt is usually a shortcut for a specific operation, it cannot completely replace traditional tools, and its interface may change with different versions to improve usability. If you use package management commands in scripts or shell pipelines, it's best to stick with apt-get and apt-cache.

Get help

In addition to web-based documentation, remember that we can get most commands from the Unix manual page (often called the man page) through the shell. For example, to read a certain page, you can use man:

In man, you can use the arrow keys to navigate. Press / to search the text within the page and use q to exit.

system	Order	illustrate
Debian / Ubuntu	man apt-get	Updating the local package database and working with packages
	man apt-cache	Search in the local package database
	man dpkg	Works with individual package files and can query installed packages
	man apt	Conduct the most basic operations through a simpler, user-friendly interface
CentOS	man yum
Fedora	man dnf
FreeBSD Packages	man pkg	Works with precompiled binary packages
FreeBSD Ports	man ports	Working with the Ports collection

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