Reviving Thunderbolt Display USB after Mac sleeps
Sometimes when I wake my MacBook Pro from sleep while it's connected to Apple's Thunderbolt Display, there is no logical connection to the USB hub on the display. Symptoms include the USB hub not showing in System Information; no power to USB devices like a Superdrive; and a USB keyboard cannot be used to wake the device, nor does it operate when the computer and display awaken.
This problem is discussed in a thread on Apple's web site: https://discussions.apple.com/message/23530645 There, use g8k3pr publishes a solution that involves changing the way the laptop handles hibernation, a mode of low power-use that retains the system-state. That is to set the hibernation to a simpler mode, known by its flags as "0". I think I improved the solution by making so that mode was only entered when powered, which we assume is when a one is using a Thunderbolt Display.
sudo pmset -c hibernatemode 0
- sudo
- "sudo" executes the following as a super-user. This is required to change power management flags.
- pmset
- "pmset" is a program to change various power management settings, to handle things like shutdown, startup, sleep, hibernation, and timers that control those things.
- -c
- The c-flag tells the power manager to apply the following settings only when a charger, like the power cord from the Thunderbolt Display, is connected. Likewise, "-b" would work when on battery-power, "-u" when on ups, and "-a" for all situations.
- hibernatemode 0
- This flag is actually a combination of several boolean flags, presented as a byte. The author of the pmset manual warns against using any mode besides 0, 3, or 25—One may render one's computer unusable.
