Every pmset sleep setting, explained

Reading your own machine

Everything below is visible in one command:

pmset -g

That prints the settings currently in effect — plus, at the top, anything currently overriding them, because assertions from running processes outrank stored settings. A SleepDisabled 1 line, for instance, means something has switched sleep off entirely.

One structural fact makes sense of the rest: most settings exist twice. There is a battery set and a charger set, and they usually differ — which is the answer to a whole family of "why does it only do this unplugged?" mysteries. pmset -b writes the battery values, -c the charger values, -a both at once.

The timers

These are *idle* timers: they answer "how long after the human stops". They are overridden by assertions — that is how caffeinate works — and they are irrelevant to the lid, which sleeps the machine regardless of any timer.

The sleep styles: hibernatemode

hibernatemode decides what "asleep" physically means. The man page documents three values, and warns you to use caution with all of them:

• 0 — sleep is memory-only. Nothing written to disk; wake is instant; power loss loses the session. The desktop default.
• 3 — memory stays powered *and* a copy is written to disk. Wake is instant from memory, and if power fails, the machine restores from the image instead of losing everything. The laptop default.
• 25 — the image is written and memory is powered off. Slower to sleep, slower to wake, and the best battery of the three. In the man page's own words: if you want hibernation, this is the setting.

Adjacent to it, standby: with it on, a laptop that has been asleep for a while writes the image and drops into the deeper state anyway — mode 3 sleep that matures into mode 25. The delay is governed by standbydelayhigh and standbydelaylow, split by whether the battery is above or below highstandbythreshold (default 50%). This is why a wake in the log can say "Wake from Hibernate" on a machine nominally in mode 3 — it slept long enough to graduate. To never write images at all, the man page's recipe is hibernatemode, standby, and autopoweroff all 0.

The network and terminal settings

• womp — wake on magic packet; the "Wake for network access" checkbox. A sleeping Mac stays reachable, at the cost of brief dark wakes to maintain its network presence.
• powernap — permits background work (mail, backups) during those display-off wakes on supported machines.
• ttyskeepawake — while a terminal session is active, no idle sleep. This is why a Mac someone is SSH'd into stays up — and the fine print is that a tty only counts as inactive once its idle time exceeds the sleep timer. More on SSH and sleep.

What none of these do

Settings shape when the machine sleeps and how deeply. No setting here wakes it at a time of your choosing — that is a different mechanism, pmset schedule for one-shots and pmset repeat for routines. And no timer value rescues a cron job whose moment passed during sleep; by the time the machine is back, the minute is gone.

Common questions

What is hibernatemode 3 vs 25?

Mode 3, the laptop default, keeps memory powered during sleep and also writes a disk image as insurance: wakes are instant, and power loss costs nothing. Mode 25 writes the image and powers memory off — slower to sleep and wake, better battery, and the man page names it the setting to use if what you want is hibernation.

Why do my pmset settings differ on battery and charger?

Settings exist per power source. pmset -b sets battery values, -c charger values, -a both — and defaults differ, which is why a Mac behaves differently plugged in. pmset -g shows the set currently in effect.

What does womp mean in pmset?

Wake on magic packet — the same thing as Wake for network access in System Settings. With it on, a sleeping Mac can be woken over the network, and it wakes briefly on its own to keep that reachability alive.

What does ttyskeepawake do?

While any terminal session (such as an SSH login) is active, the system will not idle-sleep. A tty counts as inactive only once its idle time exceeds the system sleep timer.