keepalive message not sent?

[Ahilan Anantha]

Fabrizio Bertocci <fabriziobertocci <at> gmail.com> writes:

> 
> 
> Hi All,
> Here is an interesting (but inconvenient) problem I've found with dbclient
when connected to an OpenSSH server that uses the keepalive (ClientAliveInterval
& ClientAliveCountMax).
> 
> 
> I have a OpenSSH server that sends keepalive messages to the client every 10
seconds and consider the client disconnected after 2 failed attempts.
> 
> On my client I use dbclient (latest version 0.52) to start a connection (using
a private key with no password) to setup some tunnels (local & remote).
> So far so good. When I launch the dbclient from a shell everything is fine,
this is what I see on the server log every 10 seconds:
> 
> 
> debug2: channel 1: request keepalive <at> openssh.com confirm 1
> debug1: Got 100/10 for keepalive
> debug2: channel 1: request keepalive <at> openssh.com confirm 1
> debug1: Got 100/11 for keepalive
> ...
> 
> 
> and the server keep maintaining the connection with the client.
> 
> Unfortunately, when I invoke my bourne shell script (that I use as wrapper for
launching dbclient) from the init script (/etc/init.d/myWrapper.sh), everything
SEEMS to work fine, but when the server sends keep alive messages, the dbclient
doesn't seem to respond correctly.
> This is what I see from the server's log:
> 
> 
> debug2: channel 1: request keepalive <at> openssh.com confirm 1
> debug2: channel 1: almost dead
> debug2: channel 1: gc: notify user
> debug1: session_by_channel: session 0 channel 1
> debug1: session_close_by_channel: channel 1 child 18881
> debug1: session_close_by_channel: channel 1: has child
> ...
> Disconnecting: Timeout, your session not responding.
> debug1: do_cleanup
> debug1: do_cleanup
> 
> 
> Does anybody have an idea why ?
> It has something to do with I/O probably or some settings that are available
when I launch my script (or the dbclient) from an interactive session but is
missing when is invoked from the init script...
> 
> Regards,
> fabrizio
> 
> 


So reading the OpenSSH source code... it implements "client alive" by sending an
"SSH_MSG_GLOBAL_REQUEST" (type: 80) message.

dbclient doesn't implement that message and so returns an
"SSH_MSG_UNIMPLEMENTED" (type: 3) message.

But the OpenSSH server expects either an "SSH_MSG_REQUEST_SUCCESS" (type: 81) or
"SSH_MSG_REQUEST_FAILURE" (type: 82) response.

But I don't know why it works when launching dbclient from the shell. You'd
think it would just always kick dbclient.

Regards,

Ahilan