As of focal a bunch of top-level dirs are symlinks (eg /lib -> /usr/lib) but
the deb packages still deploy files to the symlink rather than the real dir.
Thus if we just take the contents of all the *.list files we end up not
excluding lots of files that are in fact provided by debs

This package depends on a postgres server being available, but annoyingly we
can't use the 'postgresql' metapackage in the dependencies because on Ubuntu
that depends on the specific distro-provided version, which usually isn't the
one we want. So we have to add our supported Postgres versions one by one.

Can't say "keys $foo", must say "keys %{$foo}" to get the keys of a hash
pointed to by a hash reference $foo. This broke with the perl in focal.

The default prepare script now uses appropriate options if it detects Postgres
12 or higher. The error handling still needs work though.

Update prepare script for newer Postgres

Looks like Subiquity sets up a swapfile at /swap.img on Ubuntu 20.04 by default
and we certainly don't want to back that up.

We don't need these backed up, and having them in the list leads to
an error due to not having show_compatibility_56 enabled

Improve pre error handling

See merge request !1

NB this is so we can put things in LOGFILE at earlier points
than the script does at present

We capture the error code at a few points in the script, and then (intend to)
log something about what went wrong. But if we set -e we immediately bail
before logging anything useful!

Resolves #1

Resolves #3

On a new machine, there's nothing to remove and so rm will return
an error. I'd like our prepare scripts not to return errors
unnecessarily!

changed maintainer
mention name of git repository since it doesn't match package name

This repo used to have a non-standard build procedure. Now it uses
our usual makedeb process so we don't need to add extra documentation
here.

We now e.g. have a cron job on cerebro-backup which calls
these scripts, where /sbin is not on the $PATH.

For cerebro-backup where we do backups by the directory rather than the
whole server. We need to have one machine being backed up
(cerebro-filestore) but a task per directory.

NB arguably we "should" be doing this via debian/rules and
calling dh_fixperms. Doing that is left as an exercise for
whoever volunteers to refactor the way we build all of our
local debs!

The new-backup-rsnapshot script understands a 'postgres' argument, but
this set up a postgres backup in an old style that we no longer use.
This change updates it to do some of the work of setting up a new style
postgres backup and tell the user what else they might need to edit to
make it go; it varies quite a lot depending on server.

Let's not worry if we haven't backed up a machine that has been offline for 3 months (instead of 6 months)

Ignore /usr/share/doc, /usr/share/texlive - takes a long time to enumerate contents which we then exclude anyway due to being deb-provided