yum download cache & yum.conf

Sometimes, we always want to keep what you just download the packages (.rpm) via yum install ... command. Once you cloud change working directory to /var/cache/yum/.../... , and then all packages had gone after yum was completed.
/etc/yum.conf allow you to keep the cached packages and other parameter for more functions.

cachedir=/var/cache/yum    #cached packages destination
keepcache=0                #1 for keeping packages, 0 will remove the package after installed
metadata_expire=1800   # in seconds

Otherwise, you could man yum.conf for more information .