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Top Forums UNIX for Advanced & Expert Users How to Switch off a Unix machine abruptly Post 302679739 by bakunin on Tuesday 31st of July 2012 02:27:39 PM
Old 07-31-2012
One of the side results of some in-depth HACMP-tests we (some colleagues of mine and me) carried out 15 years ago was a collection of more or less ingenious ways to stop a system as fast as possible. Since then i have tested now and then these methods - more out of curiosity than for any practical purpose. These are the methods we found, listed in order from slow and safe to fast and dangerous:
  1. shutdown -h now

  2. shutdown -fh now
    Some systems use "-F" instead of "-f". Is supposed to skip some safety measures and therefore to be faster.

  3. sync ; sync ; halt
    will be even faster but might (only in extreme cases) damage the system because it stops without anything being closed in order. Still, most systems will survive this and boot more or less properly after being killed that way.

  4. halt -q
    Even faster, but don't try this without a journaling file system (don't try this at all without the need to do so). Old SunOS versions, for instance, had a fair chance of not coming up properly again after such a nosedive. Even with a journaling FS there is some risk, which is why it should only be used as either a very extreme measure or for testing purposes on expendable (test) systems. The same goes for the "winner":

  5. cat /etc/hosts > /dev/kmem
    Any other file will do too - i use this just out of habit. On POWER and PC hardware (and probably on most other hardware too) this was consistently faster than even "halt -q", it takes only about a dozen bytes to be written over the kernel image to crash the system. In AIX this is not possible any more, because even root cannot write to /dev/kmem in newer versions.

I hope this helps.

bakunin
 

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OPTIUPS(8)							    NUT Manual								OPTIUPS(8)

NAME
optiups - Driver for Opti-UPS (Viewsonic) UPS and Zinto D (ONLINE-USV) equipment NOTE
This man page only documents the hardware-specific features of the optiups driver. For information about the core driver, see nutupsdrv(8). SUPPORTED HARDWARE
optiups was originally written against a PowerES 280es in nut-0.45. It was revised for nut-2.0.1 and tested against a PowerES 420E. It is expected to work with at least the PowerES, PowerPS, and PowerVS models. This driver additionally supports a Zinto D from ONLINE USV-Systeme AG because of their very similar commands, but it is unknown if it also works with other UPS from them. This driver will not work with the PowerES stock serial cable. You will need to construct your own three conductor cable: UPS 6 -> PC 3 UPS 9 -> PC 2 UPS 4 -> PC 5 The cable for Online-USV uses pin UPS 7 (not UPS 4) -> PC 5. EXTRA ARGUMENTS
This driver supports the following optional settings in the ups.conf(5) file: status_only Only poll for critical status information. Without this, optiups (and all NUT drivers) poll all sorts of information from the UPS fairly often. It is probably not often enough to hurt anything, so this option probably is not very useful, unless you have a flaky serial connection or a highly loaded machine. nowarn_noimp Does not print warnings when the UPS reports that a variable is not implemented or not pollable. Without the option you will get a message sent to your system logs each time NUT polls the UPS. If you specify nowarn_noimp, this message will only be logged once. fake_lowbatt This forces the low battery flag true. Without it, if you want to test your UPS, you will have to unplug it and wait until the battery drops to a low/critical voltage level before NUT will respond and power down your system. With the flag, NUT should power down the system soon after you pull the plug. When you are done testing, you should remove this flag. For basic shutdown configuration testing, the command upsmon -c fsd is preferred. powerup Zinto D from ONLINE-USV cannot be identified when switched to standby. Set this flag to allow the driver to power-up your Zinto UPS. This will also power-up your equipment connected to the UPS! BUGS
On the 420E, ups.serial and ups.temperature are unsupported features. This is not a bug in NUT or the NUT driver, just the way things are with this UPS. AUTHOR
Russell Kroll, Scott Heavner, Matthias Goebl SEE ALSO
The core driver: nutupsdrv(8) Internet resources: The NUT (Network UPS Tools) home page: http://www.networkupstools.org/ Network UPS Tools 05/21/2012 OPTIUPS(8)
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