摘自：http://www.ab-weblog.com/en/creating-a-restricted-ssh-user-for-ssh-tunneling-only/
sudo useradd ssht -m -d /home/ssht -s /bin/rbash
sudo passwd ssht
sudo chmod 555 /home/ssht/
cd /home/ssht/
sudo chmod 444 .bash_logout .bashrc .profile