After update: Server refused to allocate pty

kalleboy · Aug 3, 2023

Hi, after freebsd-update fetch install and a reboot, I now cannot connect to my remote server.

My ssh client on Windows says:
End of keyboard-interactive prompts for server - Server refused to allocate pty.

I tried to clean my known_hosts ssh file on Windows, then tried to reconnect, nothing changed.

Any idea?

FreeBSD OS: 13.2

richardtoohey2 · Aug 3, 2023

Which updates were you doing?

Regular or version upgrade e.g. 13.1 to 13.2?

What platform? i386 or amd64 or arm or ?

Can you connect from another FreeBSD or Linux machine? Just to see if sshd working just not with Windows.

Have you got another machine or VM you can try the same steps on to see if you can reproduce and fix the problem?

kalleboy · Aug 3, 2023

Platform: amd64
OS: FreeBSD 13.2-RELEASE-p1 updated to FreeBSD 13.2-RELEASE-p2.

I did the same update process (freebsd-update fetch install) with 4 different servers of mine, had no such problem at all.

Tried with different ssh clients (Linux, Windows) same problem occurs.

I can have a console access I guess, but I should learn how it happened, to prevent any other remote (with no console access) servers fail like that.

covacat · Aug 3, 2023

does scp work?
or non interactive ssh
that wont need a pty

kalleboy · Aug 3, 2023

Scp works, I can access the sshd_config file as well.

It seems I have ;
StrictModes yes
PermitTTY no
in my config file.

Could one of that be the issue? If so, how it was possible to connect successfully before the update process?

yuripv79 · Aug 3, 2023

You didn't restart sshd after making changes to config file?

kalleboy · Aug 3, 2023

I did and I'm able to connect to server now.

I removed the line;
PermitTTY no
and restarted the server, the problem is gone.

Now, the question is, how come it was possible to connect to the server with that line "PermitTTY no" for many months, before the system update?

What changed?

kalleboy · Aug 3, 2023

yuripv79 said:
You didn't restart sshd after making changes to config file?

Obviously, as I said earlier, I had no terminal access to do that. Manually edited the sshd_config file and hard reset'd the server.

yuripv79 · Aug 3, 2023

kalleboy said:
Obviously, as I said earlier, I had no terminal access to do that.

All I'm saying is the following possible scenario: you had access previously, added the offending line and didn't restart sshd, so it was working for you (no reboots?)?

kalleboy said:
What changed?

Nothing in the update would have caused this, changes are completely unrelated.

kalleboy · Aug 3, 2023

Well, no, the "offending line" (PermitTTY no) was always there, since more than a year, since the first build of my server. And I was always managing the server through ssh, remotely.

After the update, I couldn't able to log in anymore. And tried to minimize my custom sshd configuration.

Obviously, the update did changed something the way sshd works. I guess?

yuripv79 · Aug 3, 2023

kalleboy said:
Obviously, the update did changed something the way sshd works. I guess?

Don't think so. Just tried fresh install of 13.2 (needed it anyway to update to stable/13, so don't mind the hostname):

Code:

> ssh fbsd-stable13
(yuri@fbsd-stable13) Password for yuri@fbsd-stable13.home.arpa:
PTY allocation request failed on channel 0

Code:

$ uname -a
FreeBSD fbsd-stable13.home.arpa 13.2-RELEASE FreeBSD 13.2-RELEASE releng/13.2-n254617-525ecfdad597 GENERIC amd64
$ grep Version /etc/ssh/sshd_config
#VersionAddendum FreeBSD-20230316