I have seen it happen on a couple of occasions where a Windows machine
(backed up via Cygwin rsyncd, not the minimal rsyncd off the SF page) will
suddenly stop working for incremental backups. Full backups will continue to
work, but incrementals will start failing with a PIPE error. For example,
here's a run where I was trying to debug with
'/usr/share/backuppc/bin/BackupPC_dump -i -v host.example.com':

  create d 770 544/1049089           0 Program Files (x86)/Common
Files/Adobe/AAMUpdaterInventory/1.0/AdobeIDCC2015AppLangen_US-11.0
  create d 770 544/1049089           0 Program Files (x86)/Common
Files/Adobe/AAMUpdaterInventory/1.0/AdobeIDCC2015AppLangen_US-11.0/11.2.0.100
Done: 0 files, 0 bytes
Got fatal error during xfer (aborted by signal=PIPE)
Backup aborted by user signal
dump failed: aborted by signal=PIPE

On the rsyncd side, the rsyncd.log says:
2016/06/09 11:26:23 [1728] connect from backuppc.example.com
(10.77.87.121)
2016/06/09 11:26:23 [1728] rsync on . from
rsyncbakup AT backuppc.example DOT com (10.77.87.121)
2016/06/09 11:26:23 [1728] building file list
2016/06/09 11:30:25 [1728] rsync: [sender] write error: Broken pipe (32)
2016/06/09 11:30:25 [1728] rsync error: error in socket IO (code 10) at
io.c(820) [sender=3.1.2]

A run with '/usr/share/backuppc/bin/BackupPC_dump -f -v host.example.com'
will run to completion, but the incremental fails, even if it's run soon
after a full is run.

I've tried updating cygwin, and the rsyncd package was updated. The fact
that I was able to upgrade a very large number of packages in the cygwin
installation, indicates to me that it wasn't a cygwin upgrade which broke
things.

This only happens to an occasional Windows machine, and it happens without
any obvious cause. Not all Windows machines will break, just one. 

Any suggestions on how to debug/fix this? the obvious workaround is just to
only do full backups, and I've done that in the past, but if I can solve
this a better way I'd like to do so.

The next step would be to uninstall and reinstall cygwin. It's possible the
problem is some corruption in a file which hasn't been upgraded and thus
repaired.
-- 
Carl Soderstrom
Systems Administrator
Real-Time Enterprises
www.real-time.com

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