[ILUG] Strange rsync issues

[Andrew McGill]

On Wednesday 20 January 2010 11:22:40 Brian O'Mahony wrote:
> I have been running about eight cron'd rsynchs from a server in Bangalore
>  to a  server in Dublin daily for the last number of years, successfully.
>  Recently however something strange has started to happen.
(y2k10 bug!)
> 
> The synchs all fire off at the same time basically. The first synch of each
>  time fails, as follows:
> 
> 
> spawn /usr/bin/rsync -av -e ssh --delete --bwlimit=0 buzz:/cvs/AppDev/
>  /cvs/AppDev/
is now a good time to ask why you're using expect instead of ssh keys?
> 
> ssh_exchange_identification: Connection closed by remote host rsync:
>  connection unexpectedly closed (0 bytes read so far) rsync error: error in
>  rsync protocol data stream (code 12) at io.c(165)
This means that the remote side accepted the TCP connection, and then closed 
it without sending the SSH banner (e.g. "SSH-2.0-OpenSSH_5.1 moo").  

> send: spawn id exp3 not open
> 
>     while executing
> 
> "send "<password>\r""
> 
>     (file "/root/cvssync" line 6)
That's collateral damage.
> 
> The next cronjob email I get, which is twelve seconds later, completes. If
>  I run it manually it completes. If I change the first cronjob in the list,
>  that is the one that fails.
> 
> Anyone have any ideas?
I'll bet the receiving server is doing a tcpwrappers check.  I'll guess your 
hosts.deny says to be unfriendly, and /etc/hosts.allow says:

	sshd: server.bangalore.in

When you connect from bangalore, tcpwrappers does the rough equivalent of:
     dig -x 88.88.88.88  (which hopefully says server.bangalore.in)
     dig server.bangalore.in (which hopefully says 88.88.88.88)

One of these DNS requests is probably failing.  When the DNS lookup is 
retried, the cached results from the first previous query allow the lookup to 
complete.  The problem may be with the DNS registration itself -- some of the 
NS servers in the chain may fail to respond (squish.net has a nice checker).  
You  may also have a poor or incorrect nameserver configured in resolv.conf.

You can use an IP address in hosts.allow, check your DNS server, create a 
/etc/hosts entry :) or hack it by making a connection to almost any port that 
will trigger a reverse DNS check.  

> 
> B
&:-)