Identify multiple users doing reverse port FWD with their pubkeys

Clément Péron peron.clem at
Wed Feb 12 22:00:18 AEDT 2020

Hi Jochen,

On Wed, 12 Feb 2020 at 00:16, Jochen Bern <Jochen.Bern at> wrote:
> On 02/11/2020 07:07 PM, Clément Péron wrote:
> > - I have X devices (around 30) and one SSH server
> > - Each of them have a unique public key and create one dynamic reverse
> > port forwarding on the server
> > - All of them connect with the same UNIX user (I don't want to create
> > a new user each time, I add a new device)
> >
> > When I connect to the server, I would like to know which pubkey as
> > open which reverse port.
> The auth happens when the device opens the SSH connection, and if your
> logging verbosity is high enough, the pubkey's fingerprint will be
> written to the log. If you really need to identify *the pubkey*, you'll
> have to grab the PID of the sshd process holding the reverse port (can
> be gleaned from the output of "{netstat,ss} -natp") and then search
> through the logs for the lines of when it got started.

Thanks for the solution, Indeed it will works but it's not really
proper, I would like to find a way like having a different parameter
for each pubkey in the authorized key file and then be able to
identify which device did the established connection.

For example I try to set an environnement variable for each pubkey in
the authorized file but can't get it when doing reverse forwarding.
Then I try to have a different permitlisten port but it doesn't work
with dynamic port :(.
Can i create a tunnel for each device or execute a specific command to
identify a posteriori which device created the reverse forwarding


> Whereas the *IP* of the device in question can be read on demand from
> the same netstat/ss output, just look for the incoming SSH connection
> held by the same PID ...
> Kind regards,
> --
> Jochen Bern
> Systemingenieur
> Binect GmbH
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> openssh-unix-dev at

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