Bad owner or permissions on /root/.ssh/config

You have used symlinks so that /root/.ssh is a symlink to /home/alexus/.ssh. Ssh is not going to like that, because it gives alexus write access to .ssh/config and all the other .ssh/* files.

You need to remove the symlink, copy the files into root's directory, and change the ownership of all of it to root. If you're doing the symlink stuff so that root and alexus share a keypair, you may be able to symlink just the id_* files into /root/.ssh/.

Something like this:

rm /root/.ssh
mkdir /root/.ssh
cp /home/alexus/.ssh/* /root/.ssh/
chown -R root /root/.ssh
rm /root/.ssh/id_*
ln -s /home/alexus/.ssh/id_* /root/.ssh/