This makes sense for user data, not the file system (or snapshot!)
itself is interesting, only the path is.
#!/bin/sh
#
# bup-save-user -- Save user data using bup(1)
-# Copyright (c)2013-2016 Alexander Barton (alex@barton.de)
+# Copyright (c)2013-2020 Alexander Barton (alex@barton.de)
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
set -x
-bup index --update --xdev --exclude-rx="/.cache/." $paths || exit 1
+bup index --one-file-system --no-check-device --exclude-rx="/.cache/." $paths || exit 1
bup save --name "$LOGNAME" $paths
exit_code=$?