How to make stable $PATH when using sudo command?

To make your sudo commands works with the $PATH of your logged-in user you just type the following command and then close all your terminals and login again:

echo "alias sudo='sudo env PATH=$PATH'" >> ~/.bashrc

How to learn linux system(hardware) properties?

To learn system(hardware,sofware) properties linux has such commands:
Operating System Version:

uname -r

Memory Information:

cat /proc/meminfo

CPU Information:

cat /proc/cpuinfo

Easy Way(smart info):

uname -rs;less /proc/meminfo grep MemTotal;less /proc/cpuinfo grep
"model name"

Aktive System Resource Usages:
(all users and all activity)

top -s

(specified user)

top -u username