CentOS / RHEL / Fedora Linux: Use Yum Command With A Proxy Server

1. proxy=http://URL:PORT/ – Proxy serer URL to the proxy server that yum should use. You must seta complete URL, including the TCP port number. If your corporate proxy server requires a username and password, specify these by adding following two settings in yum.conf file itself.
2. proxy_username=YOUR-PROXY-USERNAME-HERE (optional)- Your proxy server username to use for the proxy URL.
3. proxy_password=YOUR-SUPER-secrete-PASSWORD-HERE (optional) – Your proxy server password for this proxy URL.

Configuration: Using yum with a proxy server on a CentOS/RHEL/Fedora Linux

Login as root user and type:
# vi /etc/yum.conf
Add the following settings in [main] section:

proxy=http://server1.cyberciti.biz:3128
proxy_username=vivek
proxy_password=secretePassword

Here is a complete config /etc/yum.conf file:

[main]
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
exclude=lighttpd* nginx* spawn-fcgi* webalizer*
proxy=http://server1.cyberciti.biz:3128
proxy_username=vivek
proxy_password=secretePassword

Save and close the file. Please note that defining a proxy server, username, and password in /etc/yum.conf means that all users connect to the proxy server with those details when using yum command:
# yum update
# yum install httpd php php-gd php-mysql

How do I enable proxy access for a specific user such as root user only?

Linux and UNIX-like system has environment variable called http_proxy. It allows you to connect text based session and applications via the proxy server. Type the following command at shell prompt:
# export http_proxy="http://server1.cyberciti.biz:3128"
OR
# export http_proxy="http://PROXY=USERNAME=HERE:PROXY=PASSWORD=HERE@URL:PORT"
# export http_proxy="http://vivek:secretePassword@server1.cyberciti.biz:3128"
Feel free to add the above line in the to your shell profile file such as ~/.bash_profile. See how to set or export: http_proxy with special characters in password on a Unix or Linux based system for more information.