Re: [JSch-users] Multiple exec channels during the lifetime of a session

[Daniel F. F. <dan...@te...>]

Hi Norbert,

I have experienced this error already. After some investigations, I got=20
following conclusion.

I was running several applications concurrently on the same connection=20
using different exec channels.
On some OpenSSH servers, like on Fedora Core 5, I could create only=20
about 10 simultaneous exec channels, where on Ubuntu I could open as=20
many as I wanted. But I could not find any relationship with the OpenSSH=20
server version or Linux distro. The error was exactly the same you=20
described.

Then, I discovered that the problem is not related to the number of exec=20
channels, but with number of ptys allocated for the session. Check if=20
your exec channel does ask for a PTY by calling=20
channelExec.setPty(true). I noticed that I could create about 8 channels=20
with pty, then, on further new exec channels, I received the error your=20
mentioned. In order to open any new exec channel, _even channels that do=20
not request PTY_, the command execution failed. I had to closed some=20
other channel with PTY to be able to create new channels.

While I requested less than 8 exec channels with PTY, I could create as=20
many other without PTY as I wanted. I tested up to 150 simultaneously.

I dont think this is a Jsch problem, but I had not the opportunity to=20
test with another ssh implementation.

Do you think you could test the PTYs? I am really curious to find the=20
source of this problem.

Best regards,
Daniel Felix Ferber

Norbert Podhorszki escreveu:
> Hi,
>
> I am using JSch to execute commands on remote machines. Since I have to=
=20
> deal with machines protected with one-time-passwords, the code opens a=20
> session once and uses it to execute all commands afterwards. For each=20
> command, a separate channel is opened which is then disconnected after =
the=20
> command is executed.
>
> This has always worked fine until today when I faced two new machines.=20
> After exactly 10 successful command executions, I get an exit code 1 ba=
ck=20
> from the channel (channel.getExitStatus()) for the 11th command and for=
=20
> all consecutive ones. The command (any command, e.g. echo) is not execu=
ted=20
> at all, so this error code comes from something else on the way.
>
> The new remote machines have the same openss[hl] packages:
>    OpenSSH_4.1p1, OpenSSL 0.9.7d 17 Mar 2004
> My code has not met such a config yet, but worked fine with several=20
> combinations of 3.* and 4.* openssh and 0.9.7f and 0.9.8[ad] openssl=20
> packages.
>
> Do you have any idea, what can be the reason behind this?
>
> Thanks in advance,
> Norbert
>
>
>       Norbert Podhorszki
>     ------------------------------------
>       University of California, Davis
>       Department of Computer Science
>       1 Shields Ave, 2236 Kemper Hall
>       Davis, CA 95616
>       (530) 752-5076
>       pno...@cs...
>       ----------------------------------
>
> -----------------------------------------------------------------------=
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