SSH Advanced Techniques
At one site where I provide technical assistance, access to the network is all done via ssh over the Internet. However, one can't get access to the machines directly; one must first make an ssh connection to a gateway box I'll call martha. martha doesn't allow one to use regular passwords or keys, though. We're all given a one-time password devices the size of a credit card. When we ssh to martha, it asks us for our one-time password. The card displays a random password which we then type into the martha's password prompt. At that point we're into the system.
As the name implies, the one-time password we get from our cards can only be used once. If I tried to use that password again, martha would not let me in. This protects me from someone looking over my shoulder as I log in and trying to use that same password to get in a few minutes later.
The problem comes when I want to do anything useful with this network. Lets say I'm trying to kill a process that's using too much processor time on waldo, our web server. Step 1: in an unused terminal window I ssh to martha. I enter my PIN number on the credit card and type the password it displays to get a shell prompt on martha. Step 2: I then type "ssh waldo" to get a shell prompt on waldo (as I've already installed my ssh key there; read on if you'd like an easy way to install keys). Step 3: Then I type "su -" and enter the root password to become root. Then I can type "killall -TERM runaway_app_name ; sleep 2 ; killall -9 runaway_app_name" to kill it off.
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