How to 'do-release-upgrade' from 16.04 to 18.04 remotely using PuTTY?

[Tom H]

On Sat, Apr 6, 2019 at 2:35 PM Bo Berglund <bo.berglund at gmail.com> wrote:
>
> I have an Ubuntu Server 16.04.6 LTS. It is used as a web server,
> OpenVPN server and Subversion backup server.
>
> It is headless on Intel CPU (64 bit) hardware without both display
> and keyboard. I manage it entirely via PuTTY from my Windows7 PC.
>
> No graphical interface is installed on this server.
>
> Now on logon via PuTTY it displays this:
>
> New release '18.04.2 LTS' available.
> Run 'do-release-upgrade' to upgrade to it.
>
> When I google this command I get to pages saying it cannot be done
> remotely via SSH, is this true?
>
> Is there no way to upgrade the system to the next LTS version except
> by hooking up a keyboard and monitor to it (Only VGA video
> available....)???

Use tmux or screen (one of the first hits on google [1]).

Connect via ssh, start a tmux/screen session, kick-off the upgrade,
detach from the tmux/screen session, disconnect from ssh.

Later, connect via ssh, attach to the tmux/screen session...

The only problem that I've had, once, was to be unable to re-ssh into
the system.