CentOS 7: proxy configuration for all users

by 
vi /etc/profile

Add your proxy settings.

# set proxy config via profie.d - should apply for all users
# 
PROXY_URL="http://10.10.6.9:3128/"

export http_proxy="$PROXY_URL"
export https_proxy="$PROXY_URL"
export ftp_proxy="$PROXY_URL"
export no_proxy="127.0.0.1,localhost"

# For curl
export HTTP_PROXY="$PROXY_URL"
export HTTPS_PROXY="$PROXY_URL"
export FTP_PROXY="$PROXY_URL"