Hello,
I'm experiencing ssh-problems: I have two Mint 21.3/ Kernel 5.15.094 computers. One running MATE 1.26.0 and one running xfce 4.18.1. Also one Mac OSX 12.something.

The one running xfce can log in just fine in my RBpi. Both VNC as SSH, no problem. On the Mac I can ssh. Didn't try vnc.

But: On the MATE-device, I used to be able to ssh as well, but since a fresh install of RBpi-OS I can't ssh anymore. Strangely enough, VNC still works fine. I can (as seen over vnc) ssh into the RBpi over both 127.0.0.1 and its internal ip#. All machines are on the same /24 network. On the Mate I continuously get a timeout. As if I misspelled UID or ip#.

I tried switching off the firewall, rm known-hosts (and .old). I think somewhere I need to find prefs for the ssh-client in mate. But where are they? How about keygen? But then: why do the Mac and the xfce then still work? And what prefs are suspicious?

Any help is greatly appreciated!

I am unsure what you mean by "prefs"?
On my system:
Client settings are in /etc/ssh (ssh_conf) and /etc/ssh/ssh.d/, and in your folder ~/.ssh/.
Server settings should not be the issue, since the server side works with other clients.

Mine may not match yours, as mine is not standard Mint.

With strict host key checking you should of removed the entry in known_hosts file for all client computers?

Are you using keys only and no passwords? If keys did you remember to copy the Mate's public key to the Pi?

The -v option will provide debug information with increasing verbosity with more vs, the max is -vvv. Look at the output to see where it is failing.

ssh -vvv user@pi_ip_address

Post the output.

A users specific configuration is in ~/.ssh. System wide client configurations should be in the /etc/ssh/ssh_config file.

@wpeckham:
- with "prefs" I mean "preferences".
- locations seem to be similar on my systems. Unfortunately, both mate and xfce have same settings.

I agree with you that this problem seems to be not so much at the server.

@michaelk:
- not entirely sure what you mean by your first sentence, but what I did is "rm known-hosts" (and .old). I didn't actually change the contents of the file. Just rm.
- Actually I'm not using key at all. For now, just UID/PW. I was planning on changing just that to key, but then I couldn't ssh to RBpi anymore. So now I'm working on this ssh-thing. This also matches that I didn't copy the public keys of neither the mac and the xfce.

Please see below the output of "ssh -vvv usr@ip":

OpenSSH_8.9p1 Ubuntu-3ubuntu0.6, OpenSSL 3.0.2 15 Mar 2022
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug2: resolve_canonicalize: hostname x.x.x.x is address
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts' -> '/home/xxx/.ssh/known_hosts'
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts2' -> '/home/xxx/.ssh/known_hosts2'
debug3: ssh_connect_direct: entering
debug1: Connecting to x.x.x.x [x.x.x.x] port 22.
debug3: set_sock_tos: set socket 3 IP_TOS 0x10
debug1: connect to address x.x.x.x port 22: Connection timed out
ssh: connect to host x.x.x.x port 22: Connection timed out

Does this make sense to you? I'm lost in the last 3 lines, especially the set_sock_tos-line. What does that mean?

You might have to install nmap but post the output of the command from the Mate system.

nmap Pi_IP_address -p 22

Nmap tells that the tcp-port 22 is open for ssh.

But something strange just happened: as usual I first pinged the host (received normal reply) and then, as I tried to ssh, just to make sure nothing had changed, I suddenly got the authenticity-question! Just had to agree and now things seem to act as they should. I honestly didn't change anything... how is this possible? I could continue ssh-login en exit. After that, I did your nmap.

I'm sorry, I've been witness of some magic. Can't explain why it suddenly works. Actually, that's frustrating... I want to know why. Rebooting all systems is the only thing, but I did that many times before as well and then it didn't change a thing.

Well, at least I can continue now to disable PW-logins and go for key-login from now on.

Thanks for helping anyway!

I'm so sorry, but just as magically as it has been working for a few days, it now suddenly stopped again... nmap gives same answer: port is open for tcp. But "connection timed out" again...

Any ideas? I can ping, vcn works fine. I didn't change anything. What is happening here?