WP-CLI now has native commands for it.
# Activate Maintenance mode
$ wp maintenance-mode activate
# Deactivate Maintenance mode
$ wp maintenance-mode deactivate
wp-cli/maintenance-mode-command for more information.
If you like this question & answer and want to contribute, then write your question & answer and email to freewebmentor[@]gmail.com. Your question and answer will appear on FreeWebMentor.com and help other developers.