bug#64937: ssh sessions in systemd

[Bruno Haible]

Thorsten Kukuk wrote:
> > The only problem with this mapping is for the ut_line row, which
> > used to contain, for inbound ssh, the pty device name. It is not easy
> > to find the pty name in this situation; at least, none of the systemd
> > APIs and /run/systemd/** files that I looked at helped.
> 
> You mean you don't see a TTY on ssh sessions?

Yes, I see a session
  uid=1001 user=other state=active active=Y remote=Y \
  starttime=2023-08-01T15:19:25 seat=(null) leaderpid=40513 uiclass=user \
  pamservice=sshd vt=-1 type=tty tty=(null) \
  display=(null) desktop=(null) remotehost=::1 remoteuser=(null)

"uitype=tty" and "tty=(null)" don't make much sense together.

> openssh is really special: it does not need a TTY for all kind of ssh
> sessions, and thus only opens a TTY if needed after creating the
> logind session. Thus the logind session does not contain the TTY 
> informations.
> systemd-logind v254 provides now an interface for this case, which
> allows to set the TTY later. For openssh you need this patch:
> 
> https://github.com/thkukuk/utmpx/blob/main/patches/openssh/logind-set-tty.patch

That would make sense, yes. But I wonder:
- Why is it possible to set the "type" of the session to "tty", without
  specifying a value for the "tty"?
- While at it: Shouldn't OpenSSH also provide a value for the "remote_user"
  property?

Bruno