Apple - How bad is it for a Mac to forcefully restart it when it freezes?

Holding the power button and letting the System Management Controller SMC perform an immediate halt is no worse than letting the software initiate the halt.

I suppose you could come up with a scenario with the mac in free fall or something relating to the head not being parked, but modern hardware is designed to handle power losses from the wall outlet with great grace and here the SMC is still controlling a soft landing.

The power implications are the same even though the applications and operating system don't get their normal opportunity to save work, close files and get ready for the next time they start.

Your files and data could be at risk from this (think erase and install OS and restore backup files as worst software case), but the hardware doesn't care of the open files or some pending changes are not flushed from caches before the lights go out.

Observation

Somewhere between these two extremes:

1. the pointer alone moving (the primary symptom)
2. a forced shut down or forced restart (last resorts, with some risk)

– there may be actions that are less likely to put at risk the data; less likely to put at risk the consistency of the HFS Plus file system.

Essentially

There's on-screen movement, so:

• probably no need to kill (or force quit) the WindowServer process
• hopefully no need to force a shut down or restart of the computer.

First and second steps, and beyond

For three seconds, press and hold four keys:

• Command-Shift-Option-Esc

If the screen was not locked, then that action will Force Quit the front-most application. (The Force Quit Applications window is not required.)

If – after releasing the keys – the first force quit has no visible effect, then proceed with a second round:

• the four keys, three seconds

… and so on.

With luck a forced quit will effectively clear, from screen, the app that appeared to prevent use of the Mac.

Reference

OS X keyboard shortcuts (2012-11-02) – this document may change after OS X 10.9 is released.

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Test environment

Mountain Lion here, I don't have Lion handy to test with a normally locked screen.

Obscure side note

Avoid the four-key combination if your Mac is a client of a kernel core dump server. It might cause a USB Programmer Key debug call, a time-consuming system dump routine.