I have just been bitten by an overlooked config update from backuppc-3-3.1 to 4.4.0 in Gentoo portage and lost one month of (mostly unimportant) data.
The reason for the loss was the added "--one-file-system" config option to RsyncArgs in BackupPC 4.x that was not present in prior versions. As a result, the data of mounted partitions under a backup destination were no longer updated.
Since the main configuration file (conf/config.pl) changes significantly from 3.x to 4.x, this is an easily overlooked change that can potentially lead to very unpleasant results. Especially on existing installations with an existing backup history, the data appears to be backed up properly since one will still see the data backed up pre-4.x.
This is a change introduced by upstream, so not directly Gentoo's responsibility. Nevertheless, I feel we should at least print a warning when upgrading from 3.x to 4.x.
BackupPC 4.x configuration adds the potentially harmful '--one-file-system' option to RsynchArgs.
Remove '--one-file-system' configuration option or print a warning when upgrading from existing 3.x installations.
I think this should be done upstream in first place unless it is a pure Gentoo config.
> I think this should be done upstream in first place unless it is a pure Gentoo config.(In reply to Jonas Stein from comment #1)
> I think this should be done upstream in first place unless it is a pure
> Gentoo config.
I agree, however, the issue has been reported to upstream over a year ago and is still open despite several users supporting it (https://github.com/backuppc/backuppc/issues/341).
Until upstream fixes this, a warning at the end of an emerge would serve the community well.