On servers we configure this via ansible.

On workstations it is not having the desired effect because the stock
logrotate.conf includes the line ...

and so the simple grep thinks it's already configured! I'll add an
ansible task in due course to actually configure this.

Now that we use pygrub, these dirs are populated by quite a lot of files
that we don't want to back up but are dynamically built by the kernel/related
packages so do not make it into the the prepared "excludes" file

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

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

Our backup logs are generally full of

+ ssh -p 22 -o ConnectTimeout=10 root@openvpn2020.ch.cam.ac.uk '
  umask 077
  FILELIST=`tempfile`
  CONFLIST=`tempfile`
  mkdir -p /var/adm/backup
  # Make logrotate use datestamps
  if ! grep -q dateext /etc/logrotate.conf ; then sed  -i '\''s/^include/dateext\ninclude/'\'' /etc/logrotate.conf ; fi
  # Which packages are installed?
  dpkg --get-selections | awk '\'' { print $1 ; } '\'' >/var/adm/backup/packages
  cat /var/lib/dpkg/info/*.list | while read F ; do [ -f "$F" ] && echo "$F" ; done | sort > $FILELIST
  awk '\''/Description:/ { flag = 0 } ; flag == 1 { print $1 ; }  ; /Conffiles:/ { flag = 1  } ; '\'' </var/lib/dpkg/status |  sort >$CONFLIST
  diff -u $FILELIST $CONFLIST | grep ^-/ | sed s/^-// >/var/adm/backup/package-files
  rm
 '
rm: missing operand

because we're not escaping the args to that final rm command! This means we gradually fill
up /tmp, especially on machines that are infrequently rebooted (e.g. calculon)