rsync 2.6.3 hang (was rsync 2.6.2 crash)

Wayne Davison wayned at
Tue Oct 5 17:06:15 GMT 2004

On Tue, Oct 05, 2004 at 07:07:17AM -0700, jim wrote:
> Can you explain to me the relationship between the parent rsync
> process and it's children?

Rsync has a separate process for each major function.

The generator process (on the receiving side) has the job of figuring
out which files are different and sending checksum data for all the
files it wants to see updated.  It sends that data to the sender.

The sender has the job of taking the checksum data and generating a
stream of data that can be used to recreate the sender's file using the
receiver's file as a source of data.  It talks to the receiver process
(which is on the same system as the generator, and which actually
spawned the generator when things were starting up).

The receiver has the job of taking the update data from the sender and
turning it into the final updated files.  The final bit of communication
is that the receiver has a pipe between it and the generator that can be
used to send the generator some messages that need to be forwarded to
the sender (since it can't send things to the sender directly).

All these channels are selected for reading and writing using the
select() function.  Most of the processes are in a constant state of I/O
blocking, which is just fine going from the generator to the sender to
the receiver.  However, the channel from the receiver to the generator
has to be kept unblocked by buffering any messages that appear so that
rsync doesn't deadlock.  That should all be handled just fine unless
there is a bug.

In the trace output you sent, it looks like the sender is waiting to
write to the socket, the receiver is waiting to read from the socket,
and the generator is waiting simultaneously on reading the pipe and
writing the socket, so I don't see anything wrong there.

One thing you might try is specifying --no-blocking-io and see if that
makes a difference in the hanging you're seeing.


More information about the rsync mailing list