All 4 cores maxed out. Mac noticeably lagging.

Attempted Solution:

(Reveals wildly contradictory information.)

  1. Closed all applications
  2. Opened Activity Monitor
  3. Totaled all Process ID activity and noticed that all processes listed (including activity monitor and finder) only add up to about 10-20% CPU usage, BUT ALL 4 CORES ARE STILL REDLINED/MAXED OUT.

Additional Info:

Activity monitor also says that:

  • User Usage is < 5%
  • System Usage is almost steady at 85% (yet no PID's show significant CPU use)
  • Idle 10%

The system in question is running OS X 10.7.5 (Lion). (I'm writing from another machine.)

Three Part Question:

  2. Why is the total CPU usage drastically different from the PID list total?
  3. (BONUS) Why isn't there any system PID showing up that correlates with the 85% system usage?

1 Answer 1


NOTE: This is only a partial answer, so any other info as to why this happened could be good for others with this problem.

Literally, upon simply plugging in the power cord, all symptoms immediately stopped. (Battery was well above 10%.)

  • CPU usage dropped to normal levels.
  • Resulting sluggishness stopped as well.
  • Sounds like you somehow reset the System management Controller (SMC)
    – Maximus
    Commented Apr 1, 2014 at 15:55
  • The same exact thing happened to me after re-syncing my iCloud library. CPU was at 100% but no significant processes were showing up in Activity Monitor or htop (using command-line). As soon as I pulled at the power chord, the issue immediately went away. After pulling the power chord, however, the processes photolibraryd and Photos showed up in Activity Monitor at 90+% CPU-usage, but now the actual CPU-usage is low. Very strange behaviours, indeed.
    – leifericf
    Commented Apr 26, 2020 at 10:32
  • I eventually found the culprit. In my case, the Folding@Home client (fah) was running in the background when the power cable was connected. I had installed the client some months ago and forgotten about it. The CPU-usage had nothing to do with Apple Photos or iCloud.
    – leifericf
    Commented Apr 26, 2020 at 11:41

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