转载地址：http://blog.chinaunix.net/uid-20731487-id-3504282.html
由于种种原因，比如需要一直延用过去构筑的系统，或者是为了模拟旧版RedHat Enterprise版（RedHat的收费版，CentOS可以说是它的山寨版）等等，会有需要继续使用旧版的CentOS的情况。
这样一来我们可以正常使用yum update了。
但是由于CentOS的各个服务镜像几乎已经不支持旧版系统的升级，升级yum的时候会遇到以下问题。
# yum update Setting up Update Process Setting up repositories not using ftp,http[s],or file for repos,skipping - 4 is not a valid release or hasnt been released yet Cannot find a valid baseurl for repo: update Error: Cannot find a valid baseurl for repo: update
提示已经找不到提供升级的支持了。但如果又非要继续使用旧版CenOS呢？我们从这里得到了启示。http://mirror.centos.org/centos/4.9/readmeThis directory (and version of CentOS) is depreciated. CentOS-4 is now past EOL You can get the last released version of centos 4.9 here: http://vault.centos.org/4.9/
对，http://vault.centos.org/还提供旧版的升级，所以我们必须修改配置文件（/etc/yum.repos.d/CentOS-Base.rpeo）来定向到这个镜像站点。方法如下
- --- /etc/yum.repos.d/CentOS-Base.repo.orig
- +++ /etc/yum.repos.d/CentOS-Base.repo
- @@ -13,8 +13,9 @@
-
- [base]
- name=CentOS-$releasever - Base
- -mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
- +#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
- #baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
- +baseurl=http://vault.centos.org/4.9/os/$basearch/
- gpgcheck=1
- gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
- priority=1
- @@ -23,8 +24,9 @@
- #released updates
- [update]
- name=CentOS-$releasever - Updates
- -mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
- +#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
- #baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
- +baseurl=http://vault.centos.org/4.9/updates/$basearch/
- gpgcheck=1
- gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
- priority=1
- @@ -33,8 +35,9 @@
- #packages used/produced in the build but not released
- [addons]
- name=CentOS-$releasever - Addons
- -mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
- +#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
- #baseurl=http://mirror.centos.org/centos/$releasever/addons/$basearch/
- +baseurl=http://vault.centos.org/4.9/addons/$basearch/
- gpgcheck=1
- gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
- priority=1
- @@ -43,8 +46,9 @@
- #additional packages that may be useful
- [extras]
- name=CentOS-$releasever - Extras
- -mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
- +#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
- #baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
- +baseurl=http://vault.centos.org/4.9/extras/$basearch/
- gpgcheck=1
- gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
- priority=1
- @@ -53,8 +57,9 @@
- #additional packages that extend functionality of existing packages
- [centosplus]
- name=CentOS-$releasever - Plus
- -mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
- +#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
- #baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
- +baseurl=http://vault.centos.org/4.9/centosplus/$basearch/
- gpgcheck=1
- enabled=0
- gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
- @@ -64,8 +69,9 @@
- #contrib - packages by Centos Users
- [contrib]
- name=CentOS-$releasever - Contrib
- -mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
- +#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
- #baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
- +baseurl=http://vault.centos.org/4.9/contrib/$basearch/
- gpgcheck=1
- enabled=0
- gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
# yum update Setting up Update Process Setting up repositories update 100% |=========================| 951 B 00:00 base 100% |=========================| 1.1 kB 00:00 addons 100% |=========================| 951 B 00:00 extras 100% |=========================| 1.1 kB 00:00 Reading repository Metadata in from local files primary.xml.gz 100% |=========================| 843 kB 00:01 sqlite cache needs updating,reading in Metadata update : ################################################## 1920/1920 No Packages marked for Update/Obsoletion CentOS2，3的情况还没有确认过，理论上都行得通。不过嘛，如果没有特殊情况还是升级你的CentOS吧
