Some Linux howtodos
How to access internet through proxy, when we use yum?
In the /etc/yum.conf file, add the line below, under the line that says [main].
[main]
proxy = http://your_ip:your_port
How to access internet through proxy, when we use wget?
In the /etc/wgetrc file, add the lines below
use_proxy = on
http_proxy = your_ip:your_port
https_proxy = your_ip:your_port
How to check if a TCP port is open?
nc -v your_ip your_port