To enable yum through proxy server, open the yum.conf configuration file present in /etc/yum.conf as root

#su

#vi /etc/yum.conf

Edit yum.conf and put the http proxy server address and proxy port number in yum.conf main section
If your proxy requires a user name and password then append them also as shown below.

[main]
proxy=http://*.*.*.*:8080
# put your http proxy here followed by port number
proxy_username=your_username
#replace your_username with your username
proxy_password=your_password
#replace your_password with password of your username
cachedir=/var/cache/yum/$basearch/$releasever
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1
installonly_limit=3

#  This is the default, if you make this bigger yum won't see if the metadata
# is newer on the remote and so you'll "gain" the bandwidth of not having to
# download the new metadata and "pay" for it by yum not having correct
# information.
#  It is esp. important, to have correct metadata, for distributions like
# Fedora which don't keep old packages around. If you don't like this checking
# interupting your command line usage, it's much better to have something
# manually check the metadata once an hour (yum-updatesd will do this).
# metadata_expire=90m

finally

#yum clean all

and

#yum update


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