Re: Hangs when downloading large files

[Greg Ferrar <ferrar@xxxxxxxxxxxxxx>]

Andreas,

It didn't work to add "-l DEBUG2" to Subsystem--it complained about 
"garbage (-l)" at the end of the line. My path is slightly different, 
though:

 Subsystem       sftp    /usr/libexec/openssh/sftp-server

so maybe this has to do with the version. I tried adding "LogLevel 
DEBUG2" to the file, though, and it seems to have worked--at least, I 
get what looks like level-2 debugging from the server. I've attached the 
server's debug output, and Sawmill+libssh debug output.

I captured the server output with "tail -f" on /var/log/messages; when 
the client hung, I typed "(at this point I press control-C in the client 
window)" in the window of tail -f, and then terminated the client. So 
you'll see the line I typed in the server log, so you can see where it 
hung. It was after about 10 seconds of hang. The point of the hang seems 
to be here:

Mar  9 08:58:55 wisteria sshd[21822]: debug2: channel 0: rcvd adjust 128000
Mar  9 08:59:09 wisteria last message repeated 177 times

I ran it again and let it hang longer, and it still was 177 times.

If this is a server bug, I will be content to just document it, 
especially if there's a newer version of the server which fixes it. Do 
you know if there is?

I don't understand the sshfs code enough to know what we would have to 
do similarly. Is this a change that would be made in libssh, or is this 
a change I could make in my client program? I suspect the former; it 
seems to have to do with throttling the amount of outstanding data 
somehow, and I don't think the libssh API provides any functionality for 
determining what's outstanding. Is there some way I can implement this 
on my end?

-
Greg



Andreas Schneider wrote:
> On Tuesday 09 March 2010 01:58:02 you wrote:
>   
> > Andreas,
> >
> > Here is the debug output from the client, and from Sawmill (our
> > software). I didn't turn on logging in the server because I never have
> > (or maybe once), and I'll have to do some research to know how--if this
> > doesn't give you enough, please let me know and I'll log it from the
> > server side too.
> >     
>
> Edit /etc/ssh/sshd_config and add -l DEBUG2
>
> Subsystem       sftp    /usr/lib64/ssh/sftp-server -l DEBUG2
>
> I want to see both sides to figure out what it is happening. This looks like a 
> bug in openssh, as it works for thousands of users and just your client with 
> this server version is hitting the problem.
>
> sshfs fixed the sftp server bug by working around it. See:
>
> http://www.mail-archive.com/debian-bugs-dist@xxxxxxxxxxxxxxxx/msg305288.html
>
> Cheers,
>
>
> 	-- andreas
>
>
>
>

Attachment: serverlog.txt.gz
Description: GNU Zip compressed data

Attachment: sawmill_libssh.log.gz
Description: GNU Zip compressed data