Something wrong with KnownHosts file handling

[kke]

In my ~/.ssh/config I have:

Host 127.0.0.1
  UserKnownHostsFile=/dev/null

Still, I get hostkey mismatch errors when connecting to VMs on localhost unless I set SSH_KNOWN_HOSTS=/dev/null.

Could be #87

[danielskowronski]

Quick follow-up to k0sproject/k0sctl#813 - it seems like some incorrect merge of configs with https://cs.opensource.google/go/x/crypto/+/master:ssh/common.go since it matches my tests: order of preference for 4 of common key types is ECDSA -> RSA -> insecure DSA -> ED25519

Both OpenSSH and x/crypto/ssh will reject connection if there's at least one entry in known_hosts matching host address, but further matching to host key doesn't return anything - even if found host keys are of different types. It's a shame that ssh doesn't add everything discovered by ssh-keyscan - just first matching host key. Sidenote: OpenSSH will ignore entries matching host but not key type if key type is not on accepted list and StrictHostKeyChecking=ask.

It seems like rig/k0sctl should explicitly set ssh.ClientConfig.Config.HostKeyAlgorithms from the resolved ssh_config (or at least align with OpenSSH’s default of preferring ED25519). That way negotiation order matches what users expect, and the strict known_hosts check won’t cause any issues.