'No more sessions available' / channels not closing issue

[Mickel Daelmans | Add to Favorites]

Hi all,



We've run into a curious issue.



We run CentOS 6.5 with openssh installed (OpenSSH_5.3p1, OpenSSL 1.0.1e-fips 11 Feb 2013 by default). We connect to this server through sftp (Subsystem sftp internal-sftp) using the java JSch library. When opening many sftp channels on a single ssh session OpenSsh does not seem to release the sftp channels closed from the client side when there are still sftp channels open that are opened later than the channel that is closed..  Eventually resulting in "No more sessions available".



Here is what happens:



1) We open sftp connection (1) to server

2) We open another sftp connection (2) to server (before connection 1 is closed)

3) We close connection 1 before connection 2 is closed

4) Connection 1 will not be released because connection 2 is still open

5) We open connection 3.

6) We close connection 2, but will not be released because connection 3 is still open. Connection 1 will also not be released because 2 is not released etc..



When the connections are closed "lifo" (last in first out) all works as expected.



Is this a bug or by design? Is there a way to prevent this "leak"? Is there a way to timeout unused channels (not sessions)? We have MaxSessions raised but those will eventually max out too.


Thanks in advance,


Mickel Daelmans
Developer


Goeman Borgesiuslaan 77
3515 ET Utrecht
T. 030-7551560
W. www.addtofavorites.nl<http://www.addtofavorites.nl/>

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