Hwmond high cpu load after 10.6.8 update

Question

hwmond is causing up to 70% cpu load after every reboot on several xserves i manage caused by the update to 10.6.8. anybody else having this problem? it can be solved by hwmond -s5 to set the hwmond interval to 5 seconds but this command is not processed properly, is causing an error message "IOConnectMethodScalarIScalra0 call return err = 0xE00002BC" and has to be exited with cmd+c. Also, the com.apple.hwmond.plist in LaunchDaemons is empty.

Answer 1

In my case:
I installed 10.6.8 via the Combo Update, was running 10.6.7 previous to this.
/System/Library/LaunchDaemons/com.apple.hwmond.plist still exists and is not empty
/etc/hwmond.SMART still exists and is not empty
/etc/hwmond.conf didn't exist, so from Terminal.app I simply issued "sudo touch /etc/hwmond.conf"
I tried:
In Terminal.app, ran:sudo launchctl unload /System/Library/LaunchDaemons/com.apple.hwmond.plist
Then, backed up /usr/sbin/hwmond and /System/Library/LaunchDaemons/com.apple.hwmond.plist
From a Mac Pro running 10.6.7 Server, copied both the binary and the plist to the same spots on the Xserve, then, in Terminal.app, ran:sudo launchctl load /System/Library/LaunchDaemons/com.apple.hwmond.plist
That didn't change a thing. hwmond still spiked.
Put everything back the way it was.
And:
In Terminal.app, ran:sudo launchctl unload /System/Library/LaunchDaemons/com.apple.hwmond.plist
Backed up /System/Library/LaunchDaemons/com.apple.hwmond.plist
Made another copy to the Desktop
Edited this copy and added a string in ProgramArguments with a value of "-S255", but this still caused hwmond to spike after putting this copy back in LaunchDaemons, repairing permissions, and loading the plist via launchctl again. Any valid value still caused it to spike. However my Xserve now reboots if I set the value to an invalid value, like "-s256". Then again this also caused com.apple.hwmond and com.apple.launchd to create entries in the system log complaining about the value with hwmond attempting to relaunch itself every 10 seconds:
6/24/11 2:37:10 PM com.apple.hwmond[2697] hwmond: n should be 1 to 255 seconds
6/24/11 2:37:10 PM com.apple.launchd[1] (com.apple.hwmond[2697]) Exited with exit code: 1
6/24/11 2:37:10 PM          com.apple.launchd[1] (com.apple.hwmond) Throttling respawn: Will start in 10 seconds
OP, Armin, did something similar, but I think he tried doing it directly in Terminal, not using launchctl / launchd, which caused the error he mentioned.
Finally, added a "Disabled" item, with a boolean value of YES to the plist, recopied it, repaired permissions again (launchctl will complain and won't load the plist if you don't). This way hwmond is disabled, I can reboot my Xserve, and wait until Apple figures this out.
Full com.apple.hwmond.plist on my Xserve looks like this now:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
          <key>Label</key>
          <string>com.apple.hwmond</string>
          <key>OnDemand</key>
          <false/>
          <key>Program</key>
          <string>/usr/sbin/hwmond</string>
          <key>ProgramArguments</key>
          <array>
                    <string>hwmond</string>
                    <string>-s255</string>
          </array>
          <key>ServiceIPC</key>
          <false/>
          <key>Disabled</key>
          <true/>
</dict>
</plist>
Edit: I too have filed a bug report with a link to this thread included.
Second Edit: Server Monitor.app still works after disabling hwmond via the plist even after a reboot.
Third Edit: Sorry, keep remembering things, a modified /usr/sbin/hwmond was included the 10.6.8 Server Combo Update package, but not the Delta. Not sure if this matters. How has everyone updated to 10.6.8 so far? Like I mentioned, I used the Combo.