Tracking System Stability
When troubleshooting a sluggish Mac or diagnosing a memory leak, one of the first questions a system administrator will ask is, “When was the last time this machine was actually rebooted?” Many users simply close the lid of their MacBook, putting it to sleep for weeks or even months at a time, allowing temporary files to bloat and background processes to hang.
While you can open the System Information graphical utility to dig for the “Time since boot” metric, it is significantly faster to pull this exact metric directly from the Terminal using the classic UNIX uptime command.
Using the uptime Command
The uptime command is one of the simplest utilities in the macOS ecosystem. It requires no administrator privileges and no complex flags.
- Open the Terminal application (found in Applications > Utilities, or via Spotlight).
- Type the following command and press Enter:
uptimeDeciphering the Output
The output is a single line of text densely packed with information. It will look something like this:
14:32 up 14 days, 6:12, 2 users, load averages: 2.14 1.98 1.85Here is how to read that string:
- 14:32: The current system time (2:32 PM).
- up 14 days, 6:12: This is the actual uptime. This Mac has been running continuously for 14 days, 6 hours, and 12 minutes without a reboot.
- 2 users: The number of terminal sessions currently active (this includes your current terminal window and any background SSH connections).
- load averages: 2.14 1.98 1.85: This is a critical metric for developers. It represents the average system CPU load over the last 1, 5, and 15 minutes, respectively. If these numbers are consistently higher than the number of CPU cores your Mac has, the system is severely bottlenecked and requires a restart.
Alternative: The boottime Command
If you don’t want to do the math to figure out what day the computer was actually turned on, you can query the system kernel directly for the exact timestamp of the last boot.
Run the following command in the Terminal:
sysctl kern.boottimeThe output will return a highly specific timestamp, such as:
kern.boottime: { sec = 1704124800, usec = 0 } Mon Jan 1 08:00:00 2024This tells you the exact second the macOS kernel finished loading into memory, providing absolute proof of when the machine was last restarted.