Glossary/Figures Activity Monitor leaves out
Uptime
Also: time since restart
Quick answer
Uptime is how long a Mac has been running since it last started up. Sleep counts: closing the lid does not reset it, only a restart or a shutdown does. Activity Monitor does not show it; the `uptime` command in Terminal and System Information → Software do.
Macs are often up for weeks, because sleep is cheap and updates are the only thing that forces a restart. That is fine. macOS is built to run for months, and a long uptime is not by itself a reason to restart, whatever a support forum says about restarting every week.
Uptime becomes useful when something is wrong, because it separates the problems that a restart fixes from the ones it does not. Memory pressure that stays red after you quit the apps that caused it, a process that has been stuck for days, or kernel_task busy on a cool Mac are the restart cases. A Mac that is slow every afternoon is not.
How to see uptime on a Mac
Open Terminal and type uptime. The line reads something like 14:32 up 12 days, 3:07, followed by the load averages. System Information (hold Option and click the Apple menu) shows the same under Software → Time since boot.
Activity Monitor has no uptime figure. Its Energy tab has a 12-hour battery graph on a laptop, but nothing about when the Mac started.
When to restart, and when not to
Restart when memory pressure stays yellow or red after you have quit the apps that were using the memory, since leaked memory in a system process is freed no other way. Restart when a process is stuck and Force Quit does not clear it, and after any macOS update that asks.
Do not restart for a slow afternoon, a hot MacBook or a full disk: those have causes you can see in Activity Monitor, and they come back after the restart. Find the app instead.
- Restart: red memory pressure that does not clear, a stuck process Force Quit cannot end, an update that asks for it.
- Find the cause instead: a Mac that is slow at the same time each day, heat under load, a disk filling up, an app that keeps growing in memory.
Questions people ask
How often should I restart my Mac?
When there is a reason: an update, memory pressure that stays high after you quit the apps behind it, or a process that will not end. There is no benefit to a weekly restart on a Mac that is behaving.
Does sleep reset uptime?
No. Uptime counts from the last startup and keeps counting while the Mac sleeps. Only a restart or a shutdown resets it.
Where do I see uptime in Activity Monitor?
Nowhere. Activity Monitor does not show it. Use `uptime` in Terminal or System Information → Software → Time since boot.
Related
Step by step: Why is my Mac so slow.
Want to watch this all the time? See the best system monitors for Mac, or the best Activity Monitor alternatives. Or browse every term in the glossary.