This is the offical instructions from Docker website here.
How to check if a package is already installed on Ubuntu
Install Docker on Ubuntu Xenial 16.04
Password, Hash & Salt
Another user data leakage event happened recently. Here is an article about how to design and implement your user/password system with good hashing/salt strategies in web applications.
How to create a sudo user on CentOS
Using rz/sz to transfer files
In some cases when you cannot use “ftp/scp” to transfer files between hosts, you can try the “sz/rz” commands which use the “ZMODEM“ protocol.