From the documentation:
"Q: Why does my transfer die with something like the following error? rsync: error writing 4 unbuffered bytes - exiting: Broken pipe rsync error: error in rsync protocol data stream (code 12) at io.c(463)
or rsync: connection unexpectedly closed (24 bytes read so far) rsync error: error in rsync protocol data stream (code 12) at io.c(342)
A: This error tells you that the local rsync was trying to talk to the remote rsync, but the connection to that rsync is now gone. The thing you must figure out is why, and that can involve some investigative work.
If the remote rsync is a daemon, your first step should be to look at the daemon's log file to see if it logged an error explaining why it aborted the transfer.
Beginning with version 2.6.3, rsync now does a better job of retreiving the error from the remote process than older versions of rsync, so you may wish to try upgrading and see if you now get sent the error message from the remote rsync.
There are several common causes for a remote rsync process going away: The destination disk is full (remember that you need at least the size of the largest file that needs to be updated available in free disk space for the transfer to succeed). An idle connection caused a router or remote-shell server to close the connection. A network error caused the connection to be dropped. The remote rsync executable wasn't found. Your remote-shell setup isn't working right or isn't "clean" (i.e. it is sending spurious text to rsync).
If you think the problem might be an idle connection getting closed, you might be able to work around the problem by using a --timeout option (newer rsyncs send keep-alive messages during lulls). You can also configure ssh to send keep-alive messages when using Protocol 2 (look for KeepAlive, ServerAliveInterval, ClientAliveInterval, ServerAliveCountMax, and ClientAliveCountMax). You can also avoid some lulls by switching from --delete (aka --delete-before) to --del (aka --delete-during).
If you can't figure out why the failure happened, there are steps you can take to debug the situation. One way is to create a shell script on the remote system such as this one named "rsync-debug". You would use the script like this: rsync -av --rsync-path=/some/path/rsync-debug HOST:SOURCE DEST rsync -av --rsync-path=/some/path/rsync-debug SOURCE HOST:DEST
This script enables core dumps and also logs all the OS system calls that lead up to the failure to a file in the /tmp dir. You can use the resulting files to help figure out why the remote rsync failed.
If you are rsyncing directly to an rsync daemon (without using a remote-shell transport), the above script won't have any effect. Instead, halt the current daemon and run a debug version with core-dumps enabled and (if desired) using a system-call tracing utility such as strace, truss, or tusc. For strace, you would do it like this (the -f option tells strace to follow the child processes too): ulimit -c unlimited strace -f rsync --daemon --no-detach 2>/tmp/rsync-$$.out
Then, use a separate window to actually run the failing transfer, after which you can kill the debug rsync daemon (pressing Ctrl-C should do it).
If you are using rsync under inetd, I'd suggest temporarily disabling that and using the above daemon approach to debug what is going on."
--Steve 10:56, 11 July 2007 (EDT)