keyvalue.expirable service allow to save Key / Value variable in the database.

Example:

// Save without date limit.
\Drupal::service('keyvalue.expirable')->get('my_module')->set('my_var', 123);

Webmin and Virtualmin Change IP access control from shell terminal.

Edit file: /etc/webmin/miniserv.conf
vim /etc/webmin/miniserv.conf

Change:
allow=OLD_IP to New IP
Example:
allow=123.214.123.123 85.25.65.45 45.65.85.36

Drush allow to download and install drupal core, drupal modules and drupal themes.
Note : It is recommended to use composer to manage drupal 8, modules and themes.

SCP - Secure copy

Download a file via SCP
File :        /tmp/mysql.dump.sql
Server/Login :    THE_USERNAME:PASSWORD@domain.com
Download to :     . (Current directory)
scp user:pass@domain.com:/tmp/mysql.dump.sql .

Get HTTP Header information From JavaScript

Note : It's not possible to read the current headers. You could make another request to the same URL and read its headers, but there is no guarantee that the headers are exactly equal to the current.