prompt to update a host key

Jochen Bern Jochen.Bern at
Fri Mar 15 20:10:26 AEDT 2019

On 03/15/2019 12:49 AM, Jeremy Lin wrote:
> [...] connecting to hosts where the host key
> changes frequently. I realize this is a fairly niche use case [...]

Imagine sysadminning a boatload of VMs getting IPs from a dynamic pool, a la

> ping -c 1 -w 2 $ADDR >/dev/null 2>&1 && ssh root@$ADDR do_urgent_fix
> done

, and it mightn't be that much of a niche anymore ...

> [...] developing software for devices that often get reimaged
> (resulting in a host key change) [...]

If the host keypair(s) are truly useless for identifying a *single*,
short-lived target host, my suggestion would be to include "global"
keypairs into the image (and have them still replaced once in a while).
That would at least protect clients from a fake host set up by someone
who doesn't have access to the image or the legit hosts. (Or from
accidentally shredding a genuine "permanent" system that somehow
obtained the DNS name / IP of a short-lived one.)

If, however, reimaging is a standardized process that might allow the
new host pubkey(s) to be collected and distributed in one fell swoop,
there's the GlobalKnownHostsFile setting which is *supposed* to point to
a file maintained by the *sysadmins* ...

Jochen Bern

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