openssh unix dev - Apr 2023 - Killing the OpenSSH server doesn't cause the Windows OpenSSH client to die

Hi Rob,


On 4/7/23 10:08, Bob Rasmussen wrote:
> It depends how you "kill" the SSH server.
>
> If you kill it by sending it a SIGKILL signal, it will NOT notify the 
> client, so the client will stay running until the client discovers the 
> connection is broken. 

I run 'kill <pid>' which sends SIGTERM. This should shout it down 
gracefully.

But even with SIGKILL the OS would still shut down the network 
connection gracefully, and this should be propagated to the client.



Yuri

On Friday, April 7, 2023 1:13 PM, Yuri wrote:
>On 4/7/23 10:08, Bob Rasmussen wrote:
>> It depends how you "kill" the SSH server.
>>
>> If you kill it by sending it a SIGKILL signal, it will NOT notify the
>> client, so the client will stay running until the client discovers the
>> connection is broken.
>
>
>I run 'kill <pid>' which sends SIGTERM. This should shout it
down
>gracefully.
>
>But even with SIGKILL the OS would still shut down the network
>connection gracefully, and this should be propagated to the client.
Windows sometimes keeps sockets around until TTL expires. If you have Cygwin
or similar, netstat -a will show you any sockets that are around but no
longer connected (FIN-WAIT). If a process tries to bind to a bound socket on
the same port during that period, the bind may fail (it does not on some
platforms).

--Randall

On 4/7/2023 1:13 PM, Yuri wrote:
> On 4/7/23 10:08, Bob Rasmussen wrote:
>> It depends how you "kill" the SSH server.
>>
>> If you kill it by sending it a SIGKILL signal, it will NOT notify the 
>> client, so the client will stay running until the client discovers 
>> the connection is broken. 
>
>
> I run 'kill <pid>' which sends SIGTERM. This should shout it
down
> gracefully.
>
The <pid> you reference, is that the process for the actual windows 
client connection that was spawned off, or the server. If the server, 
the existing connections will still live.

e.g.

here are all the ssh processes on a FreeBSD server. If I kill the master 
(pid 865), my session is still alive. I just cant get new ones

#? ps -auxwww | grep ssh
root?????? 865?? 0.0? 0.2? 21072? 8816? -? Ss?? Thu11 0:00.00 sshd: 
/usr/sbin/sshd [listener] 0 of 10-100 startups (sshd)
root???? 12441?? 0.0? 0.2? 21144? 9372? -? Ss?? 13:01 0:00.02 sshd: mike 
[priv] (sshd)
mike 12443?? 0.0? 0.2? 21144? 9644? -? S??? 13:01?????? 0:00.01 sshd: 
mike at pts/0 (sshd)
root???? 12458?? 0.0? 0.1? 12816? 2340? 1? S+?? 13:01 0:00.00 grep ssh

# kill 865

# ps -auxwww | grep ssh
root???? 12441?? 0.0? 0.2? 21144? 9372? -? Is?? 13:01 0:00.02 sshd: mike 
[priv] (sshd)
mike? 12443?? 0.0? 0.2? 21144? 9644? -? S??? 13:01?????? 0:00.01 sshd: 
mike at pts/0 (sshd)
root???? 12461?? 0.0? 0.1? 12868? 2364? 1? R+?? 13:02 0:00.00 grep ssh

In the above case, I think you want to kill 12441 and its child 12443.

I just tested on a new login via the windows ssh client, and it indeed 
killed the connection when I killed the two processes on the server

 ?kill 12532 12534


0(testgateway)# Connection to 192.168.243.5 closed by remote host.
Connection to 192.168.243.5 closed.

C:\Users\mike>


 ??? ---Mike