The other day, I realized while I was at work that I needed some files from my Mac desktop at home. Normally, no problem, ssh into my firewall and open a tunnel to my desktop (this is better done with authpf, but that’s a post for another time), use sftp, and done. The problem is that because of unexplained kernel panics (probably a bad RAM module), my desktop would crash hard if left on all day, so I’ve been putting it to sleep when I go to work. Now, with my Mac set to wake for remote admin access, I ought to be able to run a wake-on-LAN utility to wake it up and be fine, except that I use a passworded screensaver. With a passworded screensaver, waking the machine locally or remotely will give 30-60-second window during which the computer is awake and expecting a password to be entered at the physical machine; there doesn’t seem to be a way to do this remotely and unlike earlier versions of OS X, since 10.3 or 10.4 or so, you can’t just kill the screensaver process from the command line (i.e. by logging in with ssh).
On the other hand, ssh is a very robust protocol and somehow ssh sessions seem to readily survive disconnect/reconnect cycles. Making use of this, it is possible to get a workable, if slow, connection to a passworded-and-sleeping Mac. On one connection to the firewall machine, run a loop of the wake-on-LAN command so that the magic packets that make the Mac wake are being sent every second or so. Use another connection to ssh into the Mac and do whatever you need to do. It helps to plan out what you need to do so that you can get the commands in fast, but even during the cycle where the Mac goes back to sleep and gets reawakened by the wake-on-LAN loop, you can type commands; they just won’t appear (not even echoed) until ssh recovers the connection.
While this is an annoying way to use a machine and it’s probably not good for the hardware to cycle in and out of sleep repeatedly in such a short time span, it does give a way to get at a passworded and sleeping Mac remotely.
