How to generate a really good, complex and long password in Linux

Okay. So you want to generate a complex, long password. Open a terminal window and use the pwgen command in Linux as follows:
$ pwgen -c -n -y -s 16 4 <enter>

-c include at least 1 capital in the password
-n include at least 1 number in the password
-y include at least 1 special character
-s generate a secure password
16 is the length of password
4 is the number of passwords to generate

If you do not find the pwgen command on your computer, say Ubuntu, then you can install it as follows:
$ sudo apt-get install pwgen <enter>

Then use the pwgen command as shown.