openssh bugs - Jun 2015 - [Bug 2413] New: Suppress 'Permanently added ... to known hosts' when redirecting to /dev/null

https://bugzilla.mindrot.org/show_bug.cgi?id=2413

            Bug ID: 2413
           Summary: Suppress 'Permanently added ... to known hosts' when
                    redirecting to /dev/null
           Product: Portable OpenSSH
           Version: 6.8p1
          Hardware: 68k
                OS: Mac OS X
            Status: NEW
          Severity: trivial
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: ben at bencreasy.com

See http://superuser.com/a/141352/457084 - it is reasonably common to
disable adding to known_hosts (sometimes I know a host just won't be
around next time), but it currently outputs 'Warning: Permanently added
'104.131.139.183' (RSA) to the list of known hosts' even when that
isn't happening. I'm noting this upstream in the interest of correct
output.

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Darren Tucker <dtucker at zip.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dtucker at zip.com.au

--- Comment #1 from Darren Tucker <dtucker at zip.com.au> ---
Well ssh *is* actually writing it, but it's being immediately discarded
outside of ssh's control.

You can already suppress the warning with LogLevel=ERROR as noted in
those links and UserKnownHostsFile=/dev/null is a pretty poor practice
anyway, so I don't think we should be doing anything to encourage it.

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--- Comment #2 from Ben Creasy <ben at bencreasy.com> ---
I see what you mean, and it is true that various workarounds are
suggested at
http://superuser.com/questions/141344/dont-add-hostkey-to-known-hosts-for-ssh/141352#141352.
In terms of what ssh is writing, I would image that ssh can figure out
whether the final output is /dev/null (of course the last thing most
people want is yet another optional switch). In my case I like being
able to have a known_hosts file that has hosts that I expect to connect
to more than once - it feels more organized. 

In my case, I'm sometimes starting up temporary DigitalOcean droplets
for a little while to test something out and then destroying them. I'd
rather not limit my logging or have to mess around with a config file
when I do that.

Is there a way to do this which doesn't require tweaking the config
files but isn't a poor practice?

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org

--- Comment #3 from Damien Miller <djm at mindrot.org> ---
Created attachment 2653
  --> https://bugzilla.mindrot.org/attachment.cgi?id=2653&action=edit
Accept UserKnownHostsFile=none

We could perhaps allow UserKnownHostsFile=none like this diff attempts

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Kenyon Ralph <kenyon at kenyonralph.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kenyon at kenyonralph.com

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Darren Tucker <dtucker at dtucker.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Darren Tucker <dtucker at dtucker.net> ---
Looks like "UserKnownHostsFile none" was added back in 8.5 however
it's
not currently documented.  We'll add this for the next release, which
should fully resolve this bug.

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #5 from Damien Miller <djm at mindrot.org> ---
OpenSSH 9.3 has been released. Close resolved bugs

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