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I am using OpenSSH version13 in a project. However every now and then nchan.c returns an error when we are trying to connect to the product using ssh, we get the following prints in the product and then the connection is closed.

channel 0: rcvd eof
output open -> drain
channel 0: obuf empty
channel 0: close_write
channel 0: output drain -> closed

All of these outputs are from nchan.c. Just reading the code and trying to see what might have happened seems impossible to me at least! Does anyone have any clue why OpenSSH might print this error messages and close the connection? I am hoping that someone is very familiar with the OpenSSH implementation to point me to the right direction!

I am using python to connect to the product, more specifically the python pexpect module. I set up a SSH connection, log in with user name, password and then I perform some commands and check output. This works all fine most of the times, but as explained earlier the connections fails every now and then. The output provided above can be seen in the product, and from pexpect an exception is thrown that it received EOF (End Of File) from the product (meaning that a connection could not be set up). That is pretty much all the printouts I get. I hope that someone can understand why OpenSSH does not want to setup the connection!

theAlse
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  • Is the "product" producing those messages? How are you trying to connect to it? If using `ssh`, provide a printout of `ssh -v` when the error occurs. – soulseekah Dec 06 '12 at 09:13
  • What you are showing us are debug messages. Are there any additional error messages logged? If yes: please added them to the debug messages in order of appearance. – alk Dec 06 '12 at 09:20
  • @soulseekah, see revised question above please – theAlse Dec 06 '12 at 10:26
  • Are you using `pxssh` from `pexpect`? Can you get more verbosity out of the runs? You need to provide more information as it's impossible to guess what's wrong. – soulseekah Dec 07 '12 at 02:08
  • @soulseekah, I use the pexpect spawn method to setup an SSH connection. I can not get more logs since we are using openssh directly and those are all the print outs I get every time it fails to set up a connection. – theAlse Dec 07 '12 at 13:36
  • Without more information it's impossible to tell, sorry. – soulseekah Dec 07 '12 at 15:51

2 Answers2

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When SSH debugging (-v) fails to give enough output, I always start sshd in debugging mode and watch from the sshd console directly. It tends to give more feedback on exactly what the root cause is.

tomlarmon
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If you are really using the version of OpenSSH you linked to, you are using an outdated version.

The latest version of OpenSSH nchan.c file can be found here: http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/nchan.c?rev=1.63;content-type=text%2Fx-cvsweb-markup and you can note the difference in version: 1.63 (dated 2010/01/26) vs 1.32 (dated 2001/10/10).

Please make sure you upgrade to the latest version of OpenSSH - I suspect you stumbled upon a bug that has been corrected a long time ago.

A.N.Onymous
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