link

/etc/ssh/sshd_config

and set log level:

LogLevel DEBUG3

Then try to authenticate, and when it fails, look for log file:

/var/log/secure

LogLevel is defined in /etc/ssh/sshd_config. The default log is/var/log/auth.log unless defined otherwise in sshd_config

It sounds like you are attempting to add a users key into root’s authorized_keys file instead of the users authorized_keys file.

Just to clarify:

roots key should be in /root/.ssh/authorized_keys

users key should be in /home/USERNAME/.ssh/authorized_keys

It is possible to store the keys in /etc/ssh as you suggested, but not in the way that you are doing it. This is generally done when the users home directory is encrypted. In order for this to work, you need to make sure the following is done:

# mkdir /etc/ssh/USERNAME
# chmod 755 /etc/ssh/USERNAME
# chown USERNAME /etc/ssh/USERNAME
# touch /etc/ssh/USERNAME/authorized_keys
# chmod 644 /etc/ssh/USERNAME/authorized_keys
# chown USERNAME /etc/ssh/USERNAME/authorized_keys
# cat /home/USERNAME/.ssh/authorized_keys > /etc/ssh/USERNAME/authorized_keys
# echo "AuthorizedKeysFile /etc/ssh/%u/authorized_keys" >> /etc/ssh/sshd_config

Note: You might want to actually edit /etc/ssh/sshd_config instead of just appending to the end, as it is possible that you already have an AuthorizedKeysFile set.