添加一个只有ssh权限的user

摘自：http://www.ab-weblog.com/en/creating-a-restricted-ssh-user-for-ssh-tunneling-only/

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sudo useradd sshtunnel -m -d /home/sshtunnel -s /bin/rbash

sudo passwd sshtunnel

sudo chmod 555 /home/sshtunnel/

cd /home/sshtunnel/

sudo chmod 444 .bash_logout .bashrc .profile