Yum is a package management utility that is used to install packages. The greatest benefit of using yum is that it automatically configures the dependency packages required for the installation and installs them as well. YUM is expanded as YellowDog Updater Modified. It is used in rpm compatible operating systems like Red Hat and Fedora/CentOS. It makes use of XML for storing repository information.
Configuring yum
YUM is stored under /etc under yum.repos.d.
The basic syntax for yum repo is
[name of repository]
baseurl=ftp://mywebsite.com
enabled=0 (or) 1
gpgcheck = 0 (or) 1
Baseurl defines the url from which the packages are to be retrieved. Enabled is whether the current repo is in on or off state. GPGcheck can be 0 or 1, depending on whether a GPG signature check needs to be performed or not.
The baseurl may be defined for HTTP/FTP websites and a few more I assume. The baseurl can be configured to use a local file system as well just use file:///(path)
For eg: baseurl = file:///root
HTH
Ananthakrishnan Ravi 
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