Mac Seems to Routinely Wake Up from Sleep

Now, I know I said this blog was going to focus mostly on virtualization and all, but every once in a while, you stumble across a tech-related issue and a fix or workaround that’s just worth sharing. This, in my opinion, is one of those times.

Occasionally, my Mac would wake itself up from sleep mode every now and again. At first, it didn’t seem like much of an issue, but I recently noticed that it seemed to be recurring at regular intervals, almost on a schedule of sorts. So, I took to the web to see if I could figure out the issue and here’s what I found:

Check the logs using Terminal

  • Open a new Terminal window (found in /Applications/Utilities) and run one of the following commands (based on your OS version):
  • For Mac OS 10.12 “Sierra”:
    log show | grep -i "wake reason"
  • For Mac OS 10.11 “El Capitan” or earlier:
    syslog | grep -i "wake reason"
  • I ran the terminal commands on my system, and in the screenshot below, the logs showed that a “Wake from sleep” instance was occurring almost every two hours!

What do these “Wake Reason” codes mean?

Ok, so my system is waking from sleep on a regular basis due to a RTC code, but what does that actually mean? Well, I found a blog post over at www.osxdaily.com that explains the codes in more detail:

  • OHC: Open Host Controller (usually a USB or Firewire device). If you see OHC1 or OHC2 it is probably an external USB keyboard or mouse that has woken up the machine.
  • EHC: Enhanced Host Controller is another USB interface, but can also be wireless devices and bluetooth since they are also on the USB bus of a Mac.
  • USB: a USB device woke the machine up
  • LID0: this is literally the lid of your MacBook portable, when you open the lid the machine wakes up from sleep
  • PWRB: Power Button, which is the physical power button on your Mac
  • RTC: Real Time Clock Alarm, is generally from wake-on-demand services like when you schedule sleep and wake on a Mac via the Energy Saver preference pane. It can also be from a launched setting, user applications, backups, and other scheduled events.

As you can see from my Terminal screenshot, I had a RTC code kicking off every two hours. Because of the RTC codes, I decided to check my settings in the Energy Saver system preferences. I also had a few UHC and EHC codes mixed in there, which was probably me (or someone in my family) clicking the mouse or keyboard to wake the system from sleep.

See if “Wake for network access” is set

  • Open System Preferences > Energy Saver
  • Uncheck: Wake for network access

See if a Schedule is set

  • While still in the System Preferences > Energy Saver window, click Schedule…
  • Ensure that Startup or wake is unchecked (unless, of course, you actually want your system to startup or sleep at a specific time).

As it turns out, my particular situation was indeed the result of “Wake for network access” being checked in the Energy Saver preference pane. After unchecking this setting, my system is no longer waking from sleep every two hours! Hopefully this post helps you to resolve your Mac’s “Wake from Sleep” woes. As always, thanks for stopping by!