5. How to set things up

The following presupposes that you have a cable that works properly with powerd.c. If you're not sure that your cable works (or how it works), see section Reverse-engineering cables and hacking powerd.c for information on dealing with poorly described cables and reconfiguring powerd.c. Sections Serial port pin assignments and Ioctl to RS232 correspondence will also be useful.

If you need to make a cable, see section How to make a cable for the overall details, and the subsection of section Info on selected UPSs that refers to your UPS. The latter might also include information on manufacturer supplied cables. You'll probably want to read all of section Info on selected UPSs because each section has afew additional generally helpful details.

• Edit /etc/inittab. Put in something like this:

  
  # What to do when power fails (Halt system & drain battery :):
  pf::powerfail:/etc/powerfailscript +5
  
  # If power is back before shutdown, cancel the running shutdown.
  pg:0123456:powerokwait:/etc/powerokscript
  
     
  

• Write scripts /etc/powerfailscript and /etc/powerokscript to shutdown in 5 minutes (or whatever's appropriate) and kill any existing shutdown, respectively. Depending on the version of shutdown that you're using, this will be either so trivial that you'll dispense with the scripts, or be a 1 line bash script, something along the lines of:

  
      kill `ps -aux | grep "shutdown" | grep -v grep | awk '{print $2}'`
  

  and you'll keep the scripts. (In case it doesn't come out right, the first single quote on the above line is a backquote, the second and third are single quotes, and the last is also a backquote.)
• Tell initd to re-process the inittab file with the command:

      telinit q
     
  

• Edit rc.local so that powerd gets run upon startup. The syntax is:

      powerd <line>
      
  

  Replace <line> with the serial port that the modem is connected, such as /dev/cua1.
• Connect PC's serial port to UPS's serial port. DO NOT PLUG PC INTO UPS YET.
• Plug a light into the UPS.
• Turn on the UPS and the light.
• Run powerd.
• Test the setup:
  • Yank the UPS's plug.
    • Check that the light stays on.
    • Check that /etc/powerfailscript runs.
    • Check that shutdown is running.
  • Plug the UPS back in.
    • Check that the light stays on.
    • Check that /etc/powerokscript runs.
    • Check that /etc/powerfailscript is not running.
    • Check that shutdown is no longer running.
  • Yank the UPS's plug again. Leave it out and make sure that the PC shuts down properly in the proper amount of time.
  • The Dangerous Part. After everything seems to be proper, powerdown the PC and plug it into the UPS. Run a script that sync's the hard disk every second or so. Simultaneously run a second script that keeps doing a find over your entire hard disk. The first is to make this a little safer and the second is to help draw lots of power. Now, pull the plug on the UPS, check again that shutdown is running and wait. Make sure that the PC shuts down cleanly before the battery on the UPS gives out. This is dangerous because if the power goes out before the PC shuts down, you can end up with a corrupt file system, and maybe even lose all your files. You'll probably want to do a full backup before this test, and set the shutdown time extremely short to begin with.

Congratulations! You now have a Linux PC that's protected by a UPS and will shutdown cleanly when the power goes out!