Re: [tlug] Ubuntu 16.04-LTS SSH authentication problems

[Raymond Wan <rwan.kyoto@example.com>]

Hi Charles,

Yes, this got me as well on one of the servers I upgraded.  Or, at
least, it sounds like something similar.

Ubuntu 16.04 is now using OpenSSH 7.x, previously, it was around 6.8
or something.  From OpenSSH 7.x, DSA keys are disabled.

See https://wiki.ubuntu.com/XenialXerus/ReleaseNotes, under the
section "OpenSSH 7.2p2".

This doesn't explain why your password doesn't work, but if you are
using a DSA key (like I was), you need to switch to something else.
Ideally, before upgrading if you're doing an ssh-based upgrade.

But, you can get around this on the client side by adding / modifying
your ~/.ssh/config and adding something like this:

Host *
  PubkeyAcceptedKeyTypes ssh-dss

(I forgot if it was ssh-dss or ssh-dsa.  Anyway, if you ssh in with
"-vvv" you will see an error message about ssh-dsX not in
PubkeyAcceptedKeyTypes .)

Oddly enough, the suggestions mentioned on the ReleaseNotes, which in
turn points to the upstream legacy documentation didn't work for me.
But the above change to config did work.  Enough for me to change to
RSA keys.

I think this is the problem you're facing, but I'm not too sure.  Hope it helps!

Ray


On Fri, Apr 29, 2016 at 3:24 PM, Charles Muller
<acmuller@example.com> wrote:
> I've tried upgrading to Ubuntu 16.04 on a few machines, with both
> Kubuntu and Gnome (in all cases running on VMware), and when I try to
> SSH to my servers, not only do I get a password prompt, but the password
> is not accepted. I duly reset the $HOME/.ssh/ permissions, to no avail.
>
> I haven't yet tried to generate a new keypair, thinking that I would
> first see if any TLUGers have encountered this problem, or might have a
> guess as to what the problem could be. I saved copies of my Ubuntu 15
> installation, so I've rolled back on my all of my other installations
> except for one, where I'd like to see if I can resolve this.
>
> Chuck
>
> ---------------------------
> A. Charles Muller
>
> Graduate School of Humanities and Sociology
> Faculty of Letters
> University of Tokyo
> 7-3-1 Hongō, Bunkyō-ku
> Tokyo 113-8654, Japan
>
> Office Phone: 03-5841-3735
>
> Web Site: Resources for East Asian Language and Thought
> http://www.acmuller.net
>
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