リポジトリの設定
日本国内では理研のサーバを指定するのが主流（らしい）なので、
yum が見に行くサーバを理研のサーバになるように変更します。
変更するファイルは /etc/yum.repos.d/CentOS-Base.repo です。
# vi /etc/yum.repos.d/CentOS-Base.repo
[base]
name=CentOS-$releasever - Base
baseurl=http://ftp.riken.jp/Linux/centos/$releasever/os/$basearch/
gpgcheck=1
#released updates
[update]
name=CentOS-$releasever - Updates
baseurl=http://ftp.riken.jp/Linux/centos/$releasever/updates/$basearch/
gpgcheck=1
#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons
baseurl=http://ftp.riken.jp/Linux/centos/$releasever/addons/$basearch/
gpgcheck=1
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
baseurl=http://ftp.riken.jp/Linux/centos/$releasever/extras/$basearch/
gpgcheck=1
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
baseurl=http://ftp.riken.jp/Linux/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
baseurl=http://ftp.riken.jp/Linux/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
#packages in testing
[testing]
name=CentOS-$releasever - Testing
baseurl=http://ftp.riken.jp/Linux/centos/$releasever/testing/$basearch/
gpgcheck=1
enabled=0
[dag]
name=Dag RPM Repository for Red Hat Enterprise Linux
baseurl=http://ftp.riken.jp/Linux/dag/redhat/el$releasever/en/$basearch/dag
gpgcheck=1
enabled=1
設定後、上書き保存します。