The short answer
kernel_task is the core of macOS, shown as a process. When the Mac gets hot, it takes CPU time on purpose so busy apps get less and the chip cools down. Apple says it responds to heat rather than causing it. You can't quit it, and you shouldn't try. Find what is heating the Mac instead: sort Activity Monitor's CPU and Energy tabs, run pmset -g therm to see whether macOS has recorded a thermal warning, and quit or pause the busiest app. kernel_task drops back on its own as the Mac cools.
On this page
What kernel_task is
kernel_task represents the macOS kernel in Activity Monitor: the part of the system that runs the hardware, memory and scheduling for every other process. Its CPU figure includes work the kernel does for the whole Mac, such as heavy disk, network and display work, so it's rarely at zero.
One of its jobs is temperature. Apple explains that when the CPU gets too hot, kernel_task makes the CPU less available to the processes using it intensely. The CPU time it shows is time it has taken away from those apps so the chip can cool, and it falls again as temperatures fall. See kernel_task and thermal state in the glossary.
Is it safe to quit kernel_task?
No, never. kernel_task is macOS itself, so it can't be quit, and there is nothing to gain from trying. Tools that limit its CPU work against the cooling it's doing. Treat a busy kernel_task as a sign, and look for the cause.
Step 1: confirm it's heat
Open Activity Monitor, click CPU and sort by % CPU. If kernel_task is near the top and the Mac feels warm or the fans are loud, heat is the likely cause. Terminal shows whether macOS has recorded it:
pmset -g thermNote: No thermal warning level has been recorded
Note: No performance warning level has been recordedIf a thermal or performance warning level is listed instead, macOS is limiting performance to cool the Mac. For a live reading, powermetrics reports the current thermal pressure level, which reads Nominal when the Mac is cool. It needs your administrator password.
sudo powermetrics --samplers thermal -n 1If kernel_task is busy but no warning is recorded and the Mac isn't warm, the kernel is doing work for something else, such as a large copy, a fast download or an external display. The next step is the same: find the app behind it.
Step 2: find what's making the heat
kernel_task doesn't make heat; other processes do. Sort the CPU tab by % CPU, then the Energy tab by Energy Impact, and look for what has been busy for minutes, not seconds. Energy impact is the best single guide to which app is warming the Mac.
top -l 2 -o cpu -n 10 -stats pid,command,cpu | tail -11The usual causes on an Apple silicon Mac:
- Long, heavy work. Video exports, games and 3D, large builds and test runs, machine learning, virtual machines.
- A runaway process. A browser tab, an app stuck in a loop, or Spotlight indexing after a macOS update.
- Nowhere for the heat to go. A MacBook on a bed, sofa or lap, a hot room or direct sun. A MacBook Air has no fan, so under a long, heavy load it slows down sooner than a MacBook Pro.
- Extra load on top. External displays and charging add a little heat. They are rarely the cause on their own, but they add up with heavy work.
Step 3: what helps
- Quit or pause the app with the highest energy impact, or let a job with an end, such as an export, finish.
- Give the Mac some air: a hard, flat surface, vents clear, out of direct sun.
- Close browser tabs that play video or animate constantly.
- If the Mac runs hot every day with light work, restart it and check Activity Monitor for anything that is always busy.
kernel_task drops back by itself once temperatures fall. There is nothing to reset.
Why kernel_task uses so much memory
kernel_task's Memory figure can be several gigabytes. It includes memory the kernel and drivers keep for the whole system, including wired memory that can't be compressed or swapped. A large, steady figure is normal. For slowness, what matters is memory pressure, not kernel_task's number.
The faster way: “What is this?” in iKnowMyMac
iKnowMyMac explains this inside the app. Every process row has a “What is this?” action that says what the process is, whether it's safe to quit, why it's busy right now and the one fix. For kernel_task, it reads the Mac's thermal state and the number of connected displays, and says which one applies.