今天需要用CentOS5.5测试个东西，但是发现在运行yum命令的时候出现下面的错误

Loaded plugins: allowdowngrade, downloadonly, fastestmirrorDetermining fastest mirrorsError: Cannot find a valid baseurl for repo: addonsYumRepo Error: All mirror URLs are not using ftp, http[s] or file. Eg. Invalid release/removing mirrorlist with no valid mirrors: /var/cache/yum/addons/mirrorlist.txt

出现这个问题的原因CentOS5版本太老，官方不再维护了，所以yum默认配置文件中的url不能再使用。

因此，需要把/etc/yum.repos.d/CentOS-Base.repo文件中的url修改了

下面是修改前的配置

# CentOS-Base.repo## The mirror system uses the connecting IP address of the client and the# update status of each mirror to pick mirrors that are updated to and# geographically close to the client.  You should use this for CentOS updates# unless you are manually picking other mirrors.## If the mirrorlist= does not work for you, as a fall back you can try the# remarked out baseurl= line instead.##[base]name=CentOS-$releasever - Basemirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/gpgcheck=1gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#released updates[updates]name=CentOS-$releasever - Updatesmirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/gpgcheck=1gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#packages used/produced in the build but not released[addons]name=CentOS-$releasever - Addonsmirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons#baseurl=http://mirror.centos.org/centos/$releasever/addons/$basearch/gpgcheck=1gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#additional packages that may be useful[extras]name=CentOS-$releasever - Extrasmirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/gpgcheck=1gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#additional packages that extend functionality of existing packages[centosplus]name=CentOS-$releasever - Plusmirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/gpgcheck=1enabled=0gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#contrib - packages by Centos Users[contrib]name=CentOS-$releasever - Contribmirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib#baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/gpgcheck=1enabled=0gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5

下面是修改后的配置

# CentOS-Base.repo## The mirror system uses the connecting IP address of the client and the# update status of each mirror to pick mirrors that are updated to and# geographically close to the client.  You should use this for CentOS updates# unless you are manually picking other mirrors.## If the mirrorlist= does not work for you, as a fall back you can try the# remarked out baseurl= line instead.##[base]name=CentOS-5.9 - Base#mirrorlist=http://mirrorlist.centos.org/?release=5.9&arch=$basearch&repo=osbaseurl=http://vault.centos.org/5.9/os/$basearch/gpgcheck=1gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#released updates[updates]name=CentOS-5.9 - Updates#mirrorlist=http://mirrorlist.centos.org/?release=5.9&arch=$basearch&repo=updatesbaseurl=http://vault.centos.org/5.9/updates/$basearch/gpgcheck=1gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#packages used/produced in the build but not released[addons]name=CentOS-5.9 - Addons#mirrorlist=http://mirrorlist.centos.org/?release=5.9&arch=$basearch&repo=addonsbaseurl=http://vault.centos.org/5.9/addons/$basearch/gpgcheck=1gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#additional packages that may be useful[extras]name=CentOS-5.9 - Extras#mirrorlist=http://mirrorlist.centos.org/?release=5.9&arch=$basearch&repo=extrasbaseurl=http://vault.centos.org/5.9/extras/$basearch/gpgcheck=1gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#additional packages that extend functionality of existing packages[centosplus]name=CentOS-5.9 - Plus#mirrorlist=http://mirrorlist.centos.org/?release=5.9&arch=$basearch&repo=centosplusbaseurl=http://vault.centos.org/5.9/centosplus/$basearch/gpgcheck=1enabled=0gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5#contrib - packages by Centos Users[contrib]name=CentOS-5.9 - Contrib#mirrorlist=http://mirrorlist.centos.org/?release=5.9&arch=$basearch&repo=contribbaseurl=http://vault.centos.org/5.9/contrib/$basearch/gpgcheck=1enabled=0gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5

修改后，重新使用yum来安装包，一切可以正常工作了。