In Ubuntu you can hibernate your PC by using the following command:

sudo systemctl hibernate

The problem is it does not automatically lock the screen. To lock the screen use:

xdg-screensaver lock

Now we can combine it together:

xdg-screensaver lock && systemctl hibernate

Note that you will need to enable your user to execute systemctl hibernate without sudo. You can do it by editing /etc/sudoers. Just add:

your-username ALL= NOPASSWD: /usr/bin/systemctl hibernate