publickey authentication on Linux Mint machine

[Bob Tennent]

I've set up publickey authentication on many systems but
this one is baffling me. Here is the relevant -vvv output of
an attempt to ssh into it:

debug1: Authentications that can continue: publickey,password
debug3: start over, passed a different list publickey,password
debug3: preferred gssapi-keyex,gssapi-with-mic,publickey,
keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/rdt/.ssh/id_rsa
debug3: send_pubkey_test
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey,password
debug1: Trying private key: /home/rdt/.ssh/id_dsa
debug3: no such identity: /home/rdt/.ssh/id_dsa: No such file or directory
debug1: Trying private key: /home/rdt/.ssh/id_ecdsa
debug3: no such identity: /home/rdt/.ssh/id_ecdsa: No such file or directory
debug1: Trying private key: /home/rdt/.ssh/id_ed25519
debug3: no such identity: /home/rdt/.ssh/id_ed25519: No such file or directory
debug2: we did not send a packet, disable method
debug3: authmethod_lookup password
debug3: remaining preferred: ,password

Why is the authentication failing? Password authentication
works okay and all the relevant permissions are okay. I get
similar results when trying from three different systems.
I've tried re-doing ssh-sysgen and ssh-copy-id, to no avail.
The .ssh/authorized_keys file looks okay. The /etc/ssh/sshd_config
has

PubkeyAuthentication yes

and I've re-started sshd.

What am I missing?

[Bob Tennent]

On Thu, 11 Nov 2021 13:15:28 -0000 (UTC), Bob Tennent wrote:
> I've set up publickey authentication on many systems but
> this one is baffling me.

I executed the following permission-setting commands
suggested in /usr/share/doc/openssh-client/faq.html

$ chmod go-w $HOME $HOME/.ssh
$ chmod 600 $HOME/.ssh/authorized_keys
$ chown `whoami` $HOME/.ssh/authorized_keys

and publickey authentication now works.