Mercurial was working for me for the most part... until I reinstalled my OS several weeks ago and tried to get back on the archive.
After cloning the archive in my file system: "hg clone -e "ssh_path -i ~/.ssh/key_path/key_name" ssh://firstname.lastname@example.org/863.10 local_archive_name"
I received the following error: "Failed to add the host to the list of known hosts(/home/rvill/,.ssh/known_hosts)."
chown username: /home/username/.ssh
chown username: /home/username/.ssh/*
chmod 700 /home/username/.ssh
chmod 600 /home/username/.ssh/*
This solved it for me.