rpm,yum and epel

在使用 Centos 安装软件的过程中，关于软件包管理工具涉及到的 yum rpm epel 三者的关系容易弄混，这里摘自wiki上的一些资料，以便区分。

yum

The Yellowdog Updater, Modified (YUM) is a free and open-source command-line package-management utility for computers running the Linux operating system using the RPM Package Manager.^[2] Though YUM has a command-line interface, several other tools provide graphical user interfaces to YUM functionality.

YUM allows for automatic updates and package and dependency management on RPM-based distributions.^[3] Like the Advanced Package Tool (APT) from Debian, YUM works with software repositories (collections of packages), which can be accessed locally^[4] or over a network connection.

Under the hood, YUM depends on RPM, which is a packaging standard for digital distribution of software, which automatically uses hashes and digisigs to verify the authorship and integrity of said software; unlike some app stores, which serve a similar function, neither YUM nor RPM provide built-in support for proprietary restrictions on copying of packages by end-users. YUM is implemented as libraries in the Python programming language, with a small set of programs that provide a command-line interface.^[5] GUI-based wrappers such as YUM Extender (yumex) also exist.^[6]

rpm

RPM Package Manager (RPM) (originally Red Hat Package Manager; now a recursive acronym) is a free and open-source package management system.^[5] The name RPM refers to the following: the <tt style="font-family: monospace, monospace;">.rpm</tt> file format, files in the .rpm file format, software packaged in such files, and the package manager program itself. RPM was intended primarily for Linux distributions; the file format is the baseline package format of the Linux Standard Base.

Even though it was created for use in Red Hat Linux, RPM is now used in many Linux distributions. It has also been ported to some other operating systems, such as Novell NetWare (as of version 6.5 SP3), IBM's AIX (as of version 4), CentOS, Fedora (operating system) created jointly between Red Hat and the Fedora community, and Oracle Linux. All versions or variants of the these Linux operating systems use the RPM Package Manager.

An RPM package can contain arbitrary set of files. Most RPM files are “binary RPMs” (or BRPMs) containing the compiled version of some software. There are also “source RPMs” (or SRPMs) containing the source code used to build a binary package. These have an appropriate tag in the file header that distinguishes them from normal (B)RPMs, causing them to be extracted to /usr/src on installation. SRPMs customarily carry the file extension “.src.rpm” (.spm on file systems limited to 3 extension characters, e.g. old DOS FAT).

epel

Extra Packages for Enterprise Linux (or EPEL) is a Fedora Special Interest Group that creates, maintains, and manages a high quality set of additional packages for Enterprise Linux, including, but not limited to, Red Hat Enterprise Linux (RHEL), CentOS and Scientific Linux (SL), Oracle Linux (OL).

EPEL packages are usually based on their Fedora counterparts and will never conflict with or replace packages in the base Enterprise Linux distributions. EPEL uses much of the same infrastructure as Fedora, including buildsystem, bugzilla instance, updates manager, mirror manager and more.