CentOS 5
Add repositories for yum
[1] Add Dag RPM Repository for yum because that has many useful packages.
[root@ns ~]#
wget http://dag.wieers.com/rpm/packages/RPM-GPG-KEY.dag.txt


[root@ns ~]#
rpm --import RPM-GPG-KEY.dag.txt

[root@ns ~]#
rm -f RPM-GPG-KEY.dag.txt

[root@ns ~]#
vi /etc/yum.repos.d/dag.repo


# create new file like below

[dag]
name=Dag RPM Repository for Red Hat Enterprise Linux
baseurl=http://apt.sw.be/redhat/el5/en/$basearch/dag/
gpgcheck=1
enabled=0


# When you use DAG repository, Input yum command like below.


[root@ns ~]#
yum --enablerepo=dag install [package]

[2] Add repository EPEL that is provided from Fedora project.
[root@ns ~]#
wget http://download.fedora.redhat.com/pub/epel/RPM-GPG-KEY-EPEL


[root@ns ~]#
rpm --import RPM-GPG-KEY-EPEL

[root@ns ~]#
rm -f RPM-GPG-KEY-EPEL

[root@ns ~]#
vi /etc/yum.repos.d/epel.repo


# create new file like below

[epel]
name=EPEL RPM Repository for Red Hat Enterprise Linux
baseurl=http://download.fedora.redhat.com/pub/epel/$releasever/$basearch/
gpgcheck=1
enabled=0


# When you use EPEL repository, Input yum command like below.

[root@ns ~]#
yum --enablerepo=epel install [package]