Channel documentation?

Peter Stuge peter at
Mon May 24 01:09:35 AEST 2021

Hi Chris,

rapier wrote:
> > If you care less about jitter then you can maybe look at SFTP but
> > probably much better any of the socket forwarding.
> So socket forwarding... I'll take a look at that.

Thinking about it again do look at SFTP too;

In particular, sftp-server can run as part of sshd when the command
"internal-sftp" is configured either in sshd_config Subsystem line
or by ForceCommand.

That might actually be a better match for your needs than the
forwarding code - if I understand correctly that you want to extract
metrics from within sshd itself.

> > If you want to implement the metric completely in the application layer
> > you could investigate creating it in a subsystem, which (like SFTP) is
> > also just a channel.
> Can that ride alongside other actions like SFTP or SCP or even just a 
> tty?

That's exactly how channels work. The ControlMaster/ControlPath
connection muxing also uses channels; a channel is added in the
original connection each time another ssh/sftp/scp command runs
and "connects" through the ControlMaster.

> Mostly I'm looking to gather metrics from real world usage. Either 
> way it looks promising.

Nod, yes, a metric channel makes perfect sense.

Kind regards


More information about the openssh-unix-dev mailing list