CentOS

sir
I just installed tomcat 7 on centos6.5.It was not the normal installation,I just extracted and copied the downloaded file to / and ran by using its startup script.I could access this server as ipaddress:8080 and default page loaded. The problem is when Itried to access manager and administration gui,it asked for username and password, I configured after googling.but it doesnt allow to login. the page which asks for username and password keeps coming back after i entered the credential.please help me on this issue. I attach my toamcat-users.xml file

Tomcat is available from epel.
Remove the one you installed and do a proper yum install.

There is nothing wrong with your installation method. Take a look at the following note in your tomcat-users.xml:

NOTE: The sample user and role entries below are wrapped in a comment and thus are ignored when reading this file. Do not forget to remove <!.. ..> that surrounds them.

I still see the quotes around the entries.

Remove from here:
<!-- <role

And here:
/>--></tomcat-users>