[CentOS] there is no priorities.conf file

Hi 

    I am new to Linux. I need to use YUM to install Software. But i
can't use YUM.

 when I give 
#yum install yum-priorities    // following error was i encountering

 Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
Could not retrieve mirrorlist
http://mirrorlist.centos.org/?release=5&arch=i386&repo=os error was
[Errno 4] IOError: <urlopen error (-2, 'Name or service not known')>
Error: Cannot find a valid baseurl for repo: base

whether i need to do any thing before to use yum properly


I have attached  /etc/yum.conf and /etc/yum.repos.d/CentOS-Base.repo
files

priorities.conf file is not there in  /etc/yum/pluginconf.d/

somebody help me in this ... thank in advance


                  







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