[root@www yum.repos.d]# yum update
Repository testing already added, not adding again
Setting up Update Process
Setting up Repos
http://mirror.centos.org/centos/4/updates/i386/repodata/repomd.xml: [Errno 4] IO Error: HTTP Error 404: Not Found
Trying other mirror.
Cannot open/read repomd.xml file for repository: update
failure: repodata/repomd.xml from update: [Errno 256] No more mirrors to try.
[root@www yum.repos.d]# yum upgrade
Repository testing already added, not adding again
Setting up Upgrade Process
Setting up Repos
http://mirror.centos.org/centos/4/updates/i386/repodata/repomd.xml: [Errno 4] IO Error: HTTP Error 404: Not Found
Trying other mirror.
Cannot open/read repomd.xml file for repository: update
failure: repodata/repomd.xml from update: [Errno 256] No more mirrors to try.
[root@www yum.repos.d]# cat CentOS-Base.repo

[base]
name=CentOS-$releasever - Base
baseurl=http://centos.cs.ucr.edu/centos/$releasever/os/$basearch/
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1

#released updates
[update]
name=CentOS-$releasever - Updates
baseurl=http://centos.cs.ucr.edu/centos/$releasever/updates/$basearch/
#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
gpgcheck=1

#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons
#baseurl=http://mirror.centos.org/centos/$releasever/addons/$basearch/
baseurl=http://centos.cs.ucr.edu/centos/$releasever/addons/$basearch/
gpgcheck=1

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
baseurl=http://centos.cs.ucr.edu/centos/$releasever/extras/$basearch/
gpgcheck=1

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
baseurl=http://centos.cs.ucr.edu/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0

#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
#baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
baseurl=http://centos.cs.ucr.edu/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0

#packages in testing
[testing]
name=CentOS-$releasever - Testing
#baseurl=http://mirror.centos.org/centos/$releasever/testing/$basearch/
baseurl=http://centos.cs.ucr.edu/centos/$releasever/testing/$basearch/
gpgcheck=1
enabled=0
[root@www yum.repos.d]#