What does the caffeinate command do on a Mac?

caffeinate is a built-in macOS command that creates power assertions telling the system not to sleep. It ships with macOS, needs no installation, and releases the assertion automatically when the command exits, so your normal sleep settings are never permanently changed.

How do I stop caffeinate?

Press Control-C in the terminal running it, or close that terminal tab. If it was started in the background, run pkill caffeinate. The assertion is released the moment the process ends, and normal sleep behaviour returns immediately.

Does caffeinate keep the Mac awake with the lid closed?

No. Closing the lid triggers a clamshell sleep that a standard caffeinate assertion cannot override, especially on battery. Keeping a Mac running with the lid shut needs a tool that handles clamshell mode, and it should only be done on power or with thermal safeguards.

Is caffeinate safe to use?

Yes. It only asks the system to stay awake for as long as the command runs, and it changes no permanent settings. The thing to watch is battery drain, since it has no low-battery cutoff of its own.

How can I check if caffeinate is working?

Run pmset -g assertions. Active assertions such as PreventUserIdleSystemSleep and PreventUserIdleDisplaySleep are listed along with the process holding them, so you can confirm caffeinate is running and see exactly what it is preventing.

Reference

caffeinate on Mac: the complete guide

Updated 12 August 2026 · 7 min read

The one-liner: caffeinate -dimsu keeps your Mac fully awake until you press Control-C. Add a command to tie it to a task (caffeinate -dimsu npm run build), or -t 3600 to hold for a set number of seconds. It's built into macOS, needs no install, and undoes itself when it exits.

Don't want to read all of this? Use the free caffeinate command builder. Pick what you're doing and it writes the exact command for you.

What caffeinate actually is

Every Mac already ships with it — there's nothing to download. When you run caffeinate, macOS creates a power assertion: a formal request that the system not sleep. It's the same underlying mechanism apps use when they say "don't sleep, I'm playing a video."

The important property is that assertions are tied to the process. When caffeinate exits, the assertion disappears and your normal sleep settings return instantly. You are never left with a Mac that won't sleep because you forgot to undo a setting — which is exactly the risk when people go poking at pmset instead.

Every flag, explained

-dPrevent the display from sleeping

-iPrevent idle system sleep

-mPrevent the disk from sleeping

-sPrevent system sleep — only on AC power

-uDeclare user activity (wakes the display)

-t <secs>Hold for a fixed time, then release

-w <pid>Wait on an existing process, release when it ends

Flags combine, which is why you see -dimsu so often — it's simply all of the main ones at once, the "keep everything awake" setting.

The commands you'll actually use

Keep the Mac awake until you stop it

caffeinate -dimsu

Runs until you press Control-C. Simple, and the most common use.

Keep it awake for exactly one hour

caffeinate -dimsu -t 3600

Time is in seconds: 1800 = 30 min, 3600 = 1 hour, 18000 = 5 hours.

Keep it awake only while a command runs

caffeinate -dimsu npm run build
caffeinate -dimsu claude
caffeinate -dimsu ./long-script.sh

This is the best pattern for scripts and long jobs. The Mac stays awake for exactly as long as the job takes, then sleep behaviour returns on its own. Nothing to remember afterwards.

Keep it awake for a process that's already running

pgrep -f "ollama"        # find the PID
caffeinate -dimsu -w 4821

Useful when you started something and only then realised the Mac might sleep on you.

Let the screen sleep but keep the machine working

caffeinate -ims

Drop the -d. The display can turn off (saving power) while the system keeps running. Good for downloads and headless jobs.

How to check that it's actually working

Don't assume — verify. This lists every active power assertion on the system, with the process holding each one:

pmset -g assertions

Look for PreventUserIdleSystemSleep and PreventUserIdleDisplaySleep set to 1, with caffeinate named as the owner. If they're not there, your command isn't doing what you think it is.

Stopping it

pkill caffeinate

Or just press Control-C, or close the terminal tab. All three work.

The three things caffeinate can't do

It's a genuinely good tool and for many people it's all they need. But it has real limits, and it's better to know them up front than to discover them at 3am with a dead job.

It can't survive a closed lid. Clamshell sleep isn't something a normal assertion overrides, particularly on battery. If you need lid-shut running, caffeinate is not the answer.
It has no idea about your battery. It will happily hold your Mac awake until the battery is flat. There is no low-power cutoff.
It won't stop if things get hot. No thermal awareness at all. Fine on a desk; less fine for an unattended overnight run.

And the practical one: you have to remember to type it, before the job starts, every single time. Miss it once on the run that mattered and you're back where you started.

Handy shortcut

If you use it constantly, alias it in ~/.zshrc:

alias stayawake="caffeinate -dimsu"
alias awake1h="caffeinate -dimsu -t 3600"

Then source ~/.zshrc and just type stayawake.

Or skip the terminal entirely

Awake is a menu-bar switch that does all of the above in one click — plus the parts caffeinate can't: lid-closed running on power, an automatic stop at 20% battery, and a cutoff if your Mac starts running hot. Free 3-day trial, no card.

Download Awake for Mac

Genuinely: if caffeinate -dimsu covers your needs, use it. It's free and it works. Awake is for when you want it automatic and safe to leave unattended.

Common questions

Do I need to install caffeinate?

No. It's built into every version of macOS. Open Terminal and it's there.

Does caffeinate work with the lid closed?

No — closing the lid triggers a clamshell sleep that a standard assertion can't override, especially on battery. That needs a clamshell-capable app, and should only be done on power or with thermal safeguards.

Will it drain my battery?

It can. caffeinate has no low-battery cutoff — it holds until you stop it. Use -t to bound it, or a tool with a battery guard.

What's the difference between -i and -s?

-i prevents idle sleep (the timer-based kind). -s prevents system sleep more broadly but only applies on AC power. Using both is the safe default.

Can I make it permanent?

You can with pmset, but don't — it changes system settings that stay changed until you undo them, and it's easy to forget. caffeinate's whole advantage is that it cleans up after itself.