create user for ssh no shell

init-user-noshell.sh

# ensure you have nologin
#
# less /etc/shells
# which nologin
#     /usr/sbin/nologin
# echo `which nologin` >> /etc/shells

useradd -m -s /usr/sbin/nologin public

# login without password
# http://www.linuxproblem.org/art_9.html

# ssh-keygen -t rsa
# cat .ssh/id_rsa.pub | ssh public@host 'cat >> .ssh/authorized_keys'

# ssh -CD 8888 -N public@host