I am seeking to find a Macbook Air serial number from within the backup files created by the Mountain Lion operating system and stored on an external hard drive. Exactly which file do I need to be looking at? I made the presumption that the backup created by time machine would store the uuid to ensure that the physical MAC address (7 layer OSI model) would be the one that received the backed up files of the MacBook Air. Perhaps in Extended Firmware Interface (EFI) folder although I did see a file mentioned; in a post elsewhere which was com.apple.TimeMachine.MachineID.plist. The same post also said that a sparse bundle created by time machine contained the hardware UUID (effectively the serial number?).

  • I'm not aware of a place even on the boot drive where the serial gets logged as a matter of routine or standard practice. What precise backup mechanism is in place in case it perhaps adds this tidbit somewhere? Time Machine?
    – bmike
    Commented Jun 3, 2014 at 13:16
  • Cant you check online against the registered apple ID?
    – bobbyalex
    Commented Jun 4, 2014 at 1:49

4 Answers 4


The UUID is not the same as the serial number.

When you use any Mac, some machine-specific preference files are created in your Library/Preferences/ByHost/ directory. The filenames are of the form


So, if you really want the UUID of a previously used machine, you can probably dig it up from some backups in that way. I don't know how useful that would be though.

I think TimeMachine stores UUIDs of the filesystem, but not the computer itself. Checking the logs on one of our servers here, I see several fsUUID and eventDBUUID but nothing for the machine.

  • 2
    Thanks to "Kent" I found the RootVolumeUUID in this file MacintoshHD/Library/Preferences/com.apple.TimeMachine.plist which is something to give the police as opposed to a serial number.
    – Alex
    Commented Jun 5, 2014 at 12:23

The serial number isn't read from a system file. It's a hardware information read directly from the hardware.

  • Can you expand on this? How does the System Information app display the serial number?
    – Dillon
    Commented Jun 3, 2014 at 13:53
  • This is (very) low level programming : It's read from a hardware memory space, probably the EFI which is located in the computer and not the hard drive. Commented Jun 3, 2014 at 14:12

It could be written to the disk if you had previously run the system profiler. This is the same as "About this Mac" except information is dumped into the Terminal. You could save the report thusly:

system_profiler > ~/systeminfo.txt

Otherwise the serial as mentioned is read directly from the logic board and generally not logged to disk.


Run in Terminal:

system_profiler SPHardwareDataType

which would print your Hardware UUID and Serial Number.

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