Install TestLink

1. yum install mysql
yum install mysql-server

2. Add CentOS-Testing repo
cd /etc/yum.repos.d/
wget http://dev.centos.org/centos/5/CentOS-Testing.repo
( edit .repo file, enabled=1)

3. yum install php php-mysql php-gd php-ldap

4. service mysqld start
chkconfig mysqld on
$ mysqladmin -u root password NEWPASSWORD

5. service httpd start
chkconfig httpd on

6. cp testlink-1.9.1.tar.gz /var/www/html/
cd /var/www/html/
tar zxvf testlink-1.9.1.tar.gz
mv testlink-1.9.1 testlink
rm testlink-1.9.1.ta.gz
chown -R apache:apache testlink
mkdir  /var/testlink
mkdir /var/testlink/logs
mkdir /var/testlink/upload_area
chown apache:apache /var/testlink/logs
chown apache:apache /var/testlink/upload_area

7. edit /etc/php.ini
session.gc_maxlifetime = 2400
max_execution_time = 120
memory_limit = 64M

8. service httpd restart

9. go to "http://localhost/testlink/

10. step by step install

11.To have a fully functional installation You need to configure mail server settings, following this steps

• copy from config.inc.php, [SMTP] Section into custom_config.inc.php.
• complete correct data regarding email addresses and mail server.

12. after installation, remove /install directory

Reference:
http://www.cyberciti.biz/faq/mysql-change-root-password/