[Koha] Upgrade OS - Ubuntu 18.04 to 20.04

[Mark Alexander]

Excerpts from Alvaro Cornejo's message of 2021-06-25 18:25:51 -0500:
> We also use a VPS provider (Linode) for the koha hosting.
> 
> What we do when migrating to a major version is to create a new VPS,
> install everything from scratch, move the DB from the old system to the new
> one, do the DB conversion and test that everything goes as expected.

I also use Linode, but I have done a similar upgrade without creating a
second VPS and migrating the database.  Perhaps that's living a bit
dangerously, but it worked for me.  I used Linode's backup feature to
give me an escape route if something went wrong.  Briefly, here's what
I did:

I shutdown the machine completely, and created a manual backup of the
entire machine.  After rebooting, I did the upgrade from Debian 8 to
Debian 9.  This was done using various apt commands.  I recall that I
had to use Linode's out-of-band ssh service instead of normal ssh at
one point, because the upgrade brought down Debian's network service
briefly.

After the OS upgrade, I made another manual backup of the entire machine.
I also made a backup of the Koha database and configuration, and copied those
files to my own laptop.  Finally, I did the Koha upgrade using the usual
'apt install koha-common'.

-- 
Let's organize this thing and take all
the fun out of it. --Ashleigh Brilliant