An important aspect of administering a CentOS server is to understand its package management system and its various online repositories. Together they ensure you are always running a secure and updated server.
CentOS uses the Yellow Dog Updater, Modified (yum) package manager to install and update software packages in RPM format from online software repositories. With yum, in addition to downloading and installing new packages, you can also check for available updates and fetch information about available packages.
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Source: Linux