Can’t login into Synology by ssh

Several months ago I find I can’t login into my Synology DS216j anymore via ssh. I used my private key to login but I got Permission denied (publickey) as responds.

I have modified sshd_config on the NAS so there was no other methods to login into it.

I am not sure if this is related but there are quite many users have this problem, according to this discussion thread:

“https://community.synology.com/enu/forum/1/post/125859”

Since there is no built-in terminal in DSM, I looked around to find a way to edit the sshd_config without ssh. And the answer is pretty much simple: just turn on telnet, login-in via telnet to modify sshd_config, and turn off telnet.

Done.