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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<TITLE>rsync current issues</TITLE>
<style>
code {
font-family: monospace;
font-weight: bold;
white-space: pre;
}
pre code {
display: block;
font-weight: normal;
}
blockquote pre code {
background: #f1f1f1;
}
</style>
</HEAD>
<!--#include virtual="header.html" -->
<H2 align="center">current issues and debugging</H2>
<ol>
<li><p><b>Q:</b>
Rsync appears hung -- what should I do?
<p><b>A:</b>
When experiencing a hang or freeze <b>please</b> gather the following
information before killing the rsync process:
<ul>
<li> The state of the send/receive queues shown with netstat on the two ends.
<li> The system call that each of the 3 processes is stuck in (use truss on
solaris, strace on Linux, etc.).
</ul>
<p>Try telling rsync on both sides of the connection to send messages to
stderr, which might make the failure message visible. i.e., use:
<blockquote<pre><code>
--msgs2stderr -M--msgs2stderr
</code></pre></blockquote>
<p>That alone might get rsync to stop hanging. Also, if you're using more than
one <code>--verbose</code> (<code>-v</code>) option then I have 2 simple words
for you: stop it. If you need more info on what rsync is changing, using the
<code>--itemize-changes</code> option (<code>-i</code>) and repeat it if you
need to see unchanged files. This is a much better way to go that doesn't fill
up the communication pipeline with a large quanity of debug messages.
<p>See the "rsync-debug" script below for an example of how to grab strace
information from the remote rsync process(es). If you need help, send email to
the mailing list.
<li><p><b>Q:</b>
Why does my chrooted rsync daemon crash when doing an LDAP lookup for a user or
group?
<p><b>A:</b>
There is a bug in some LDAP libraries (e.g. Fedora Core 3) where it crashes
when someone looks up a name from inside a chrooted process (one that does not
contain copies of the libraries to perform the lookup). This is a bug that the
LDAP libraries will need to fix, and is out of rsync's hands. You can work
around the problem by using the <code>--numeric-ids</code> option, turning
chroot off, or getting rid of LDAP lookups.
<li><p><b>Q:</b>
Why does my transfer die with something like the following error?
<blockquote><pre><code>
rsync: error writing 4 unbuffered bytes - exiting: Broken pipe
rsync error: error in rsync protocol data stream (code 12) at io.c(463)
</code></pre></blockquote>
<p>or
<blockquote><pre><code>
rsync: connection unexpectedly closed (24 bytes read so far)
rsync error: error in rsync protocol data stream (code 12) at io.c(342)
</code></pre></blockquote>
<p><b>A:</b>
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 <b>why</b>, and that can involve some investigative work.
<p>It is a good idea use the <code>--msgs2stderr</code> options mentioned at
the top of this page to get rsync to output any errors it encounters to stderr
instead of trying to write them down the failing pipeline.
<p>If the connection is via ssh (or other remote-shell command) then you should
run some tests to make sure that you can actually run the remote rsync and that
your shell isn't injecting extraneous output into the rsync stream. For instance,
try running these two commands using whatever HOST (and user) options you need:
<blockquote><pre><code>
echo hi | ssh HOST cat
ssh HOST rsync --version
</code></pre></blockquote>
<p>The first command should output just the string "hi" and nothing else. The
second command should successfully start the remote rsync and report its version.
<p>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. Also double-check to ensure that the log file is setup right, as a
wrong "log file" setting in your rsyncd.conf file can also cause this problem.
You could also halt the daemon and run it interactively using the
<code>--no-detach</code> and <code>--msgs2stderr</code> options and look for
errors while someone tries the rsync copy in another window.
<p>As for the cause of the remote rsync going away, there are several
common issues that people run into:
<ul>
<li>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).
<li>An idle connection caused a router or remote-shell server to close
the connection.
<li>A network error caused the connection to be dropped.
<li>The remote rsync executable wasn't found.
<li>Your remote-shell setup isn't working right or isn't "clean"
(i.e. it is sending spurious text to rsync).
</ul>
<p>If you think the problem might be an idle connection getting closed, you
might be able to work around the problem by using a <code>--timeout</code>
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
<code>--delete</code> (aka <code>--delete-before</code>) to <code>--del</code>
(aka <code>--delete-during</code>).
<p>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
<a href="rsync-debug">this one named "rsync-debug"</a>.
You would use the script like this:
<blockquote><pre><code>
rsync -av --rsync-path=/some/path/rsync-debug HOST:SOURCE DEST
rsync -av --rsync-path=/some/path/rsync-debug SOURCE HOST:DEST
</code></pre></blockquote>
<p>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.
<p>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 <i>strace</i>, <i>truss</i>, or
<i>tusc</i>. For strace, you would do it like this (the -f option
tells strace to follow the child processes too):
<blockquote><pre><code>
ulimit -c unlimited
strace -f -t -s 1024 -o /tmp/rsync-$$.out rsync --daemon --no-detach
</code></pre></blockquote>
<p>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).
<p>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.
<li><p><b>Q:</b>
Why does my connection to an rsync daemon (using the "::" syntax)
fail immediately with an error like the following?
<blockquote><pre><code>
rsync: connection unexpectedly closed (24 bytes read so far)
rsync error: error in rsync protocol data stream (code 12) at io.c(342)
</code></pre></blockquote>
<p><b>A:</b>
Older rsync daemons (before 2.6.3) were unable to return errors that were
generated during the option-parsing phase of the transfer. Look in the
logfile on the server to see if an error was reported, such as a "refused"
option, an option that the server rsync doesn't support (e.g. perhaps
links are not supported by the server), or some other failure (such as
trying to send data to a read-only module). Upgrading the version of rsync
that is running as a daemon to at least 2.6.3 will allow these errors to
get returned to all rsync clients, old or new alike.
</ol>
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