補充一點這是國外網站上的資訊：（大意是說，預設的 CentOS-Base.repo 之中有一個地方的資訊拼錯了，大家要記得手動去修改一下）
CentOS Errata and BugFix Advisory CEBA-2005:0506-01 for centos-yumconf
centos-yumconf contains the base configuration for yum in CentOS-4 (in the file /etc/yum.repos.d/CentOS-Base.repo) There was a misspelling in the normally disabled "contrib" repository (it was misspelled as contribs). This prevented being able to enable the contrib directory via the command-line and is corrected with this update.
The following updated files have been uploaded and are currently syncing to the mirrors:
i386 and x86_64:
You can get this update with the command:
yum update centos-yumconf
(If you have modified the file /etc/yum.repos.d/CentOS-Base.repo, a new file named CentOS-Base.repo.rpmnew will be created in /etc/yum.repos.d, and you will have to modify your CentOS-Base.repo to contain the new contrib information)