Time (in seconds) after which the metadata will expire. So that if the current metadata downloaded is less than this many seconds old then yum will not update the metadata against the repository. If you find that yum is not downloading information on updates as often as you would like lower the value of this option. You can also change from the default of using seconds to using days, hours or minutes by appending a d, h or m respectively. The default is 6 hours, to compliment yum-updatesd running once an hour. It's also possible to use the word "never", meaning that the metadata will never expire. Note that when using a metalink file the metalink must always be newer than the metadata for the repository, due to the validation, so this timeout also applies to the metalink file.