Prioritized checklist for when configuring public key authentication on SSH server (unix, synology)

Let's say that you want to access to SSH server as below:

[user]@[server_address]

1. Does public key of client is appended to server's '/home/user/.ssh/authorized_keys' file?

- In synology, location of user's home directory could be different to ordinary unix.

2. Check server's ssh daemon setting.

- Make sure to uncomment : PubkeyAuthentication yes

- Make sure to uncomment : AuthorizedKeyFiles .ssh/authorized_keys

- Make sure to uncomment : ChallengeResponseAuthentication no

2. Ownership(user, group both) of '.ssh' directory and descendants.

- In unix, [user]:[user]

- In synology, [user]:users

3. Permission of '.ssh/authorized_keys' : 0644

4. Permission of '.ssh' directory : 0700