rsync suddenly hanging indefinitely during transfers

Question

For the past few years, I have been using an rsync one-liner to back up important folders on my Mac Mini desktop (OSX 10.9, 2.5 GHz i5, 4 GB RAM) to a FreeNAS box (0.7.2 Sabanda

Answer 1

I've seen this quite often on 3.0.9 on a directory with hardlinks, but it also happened on 3.1.3.

There is a nice analysis in Debian bug 820916: when its internal sockets are congested with errors, rsync could go into a deadlock.

This might have been fixed in a 3.2 release just a few days ago (Jun 2020):

Avoid a hang when an overabundance of messages clogs up all the I/O buffers.

The only good workaround I can think of is, if the problem is not persistent, then put timeout in front of it: timeout rsync , then retry. If it is persistent for you, you're the lucky one who can debug it :D