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Just take your time and double-check everything to ensure you didn't mistype 
anything, so you won't find yourself with a server that cannot connect.
To actually make these changes take effect, you can run the following command:
sudo netplan apply
When you run the previous command, it will let you know if there are any errors in 
the file or apply the changes if not. The new IP address will take effect immediately.
In the case of utilizing remote connections such as OpenSSH while configuring 
networking, you can work around the issue of being disconnected and having 
networking not restart properly by using 
tmux
, a popular terminal multiplexer. A 
full run-through of 
tmux
 is beyond the scope of this book, but it is helpful to us in 
this scenario because it keeps commands running in the background, even if our 
connection to the server gets dropped. To use it, first install the package:
sudo apt install tmux 
Then, activate 
tmux
 by simply typing 
tmux
 in your shell prompt.
From this point on, 
tmux
 is now responsible for your session. If you run a command 
within 
tmux
, it will continue to run, regardless of whether or not you're attached to it. 
To see this in action, first enter 
tmux
 and then execute the 
top
 command. While 
top
 is 
running, disconnect from 
tmux
. To do that, press 
Ctrl
 + 
b
 on your keyboard, release, 
and then press 
d
. You'll exit 
tmux
, but if you enter the 
tmux a
 command to reattach 
your session, you'll see that 
top
 was still running even though you disconnected. 
Following this same logic, you can activate 
tmux
 prior to executing the 
sudo netplan 
apply
 command. Most likely, you'll still get dropped from your shell, since the 
process of activating network changes brings the network interface down and then 
back up again, but with 
tmux
 the command will complete in the background. You can 
then reconnect to the server and run 
tmux a
 to rejoin your 
tmux
 session.
The 
tmux
 utility is extremely powerful, and when harnessed 
can really enhance your workflow when using the Linux shell. 
Although a complete tutorial is outside the scope of this book, I 
highly recommend looking into using it. For a full walkthrough, 
check out the book 
Getting Started with tmux
 by Victor Quinn, 
J.D. at 
https://www.packtpub.com/hardware-and-creative/
getting-started-tmux
 or check out some tutorial videos on 
YouTube, such as my own series on the subject at 
learnlinux.tv
.

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