安装Fedora 15 后发现一个问题，就是yum 安装时候老是出现HTTP Error 404等问题，看：
[root@ yum.repos.d]# yum search openssh
Loaded plugins: langpacks, presto, refresh-packagekit
: [Errno 14] HTTP Error 404 - Not Found :
Trying other mirror.
: [Errno 14] HTTP Error 404 - Not Found :
Trying other mirror.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: fedora-firefox4. Please verify its path and try again
然后我索性把全部源给更换掉，找到了一些教育网的源，如上海交大的。
为了以防万一，我先备份原来的源：
[root@ etc]# mkdir yum.repo.bak[root@ etc]# mv yum.repos.d/* yum.repo.bak/
新建一个源文件*.repo
[root@ yum.repos.d]# vim sjtu.repo
粘贴一下内容：
[Fedora-ftp.sjtu.edu.cn]
name=Fedora 15 - i386
baseurl=http://ftp.sjtu.edu.cn/fedora/linux/releases/15/Fedora/i386/os/
enabled=1
gpgcheck=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-Fedora file:///etc/pki/rpm-gpg/RPM-GPG-KEY
[Everything-ftp.sjtu.edu.cn]
name=Everything 15 - i386
baseurl=http://ftp.sjtu.edu.cn/fedora/linux/releases/14/Everything/i386/os/
enabled=1
gpgcheck=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-Fedora file:///etc/pki/rpm-gpg/RPM-GPG-KEY
[updates-ftp.sjtu.edu.cn]
name=Fedora updates
baseurl=http://ftp.sjtu.edu.cn/fedora/linux/updates/15/i386/
enabled=1
gpgcheck=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-Fedora file:///etc/pki/rpm-gpg/RPM-GPG-KEY
保存退出后，执行源更新命令就ok了
[root@ yum.repos.d]# yum update
更新速度很给力，达到4，5M/s