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Mac Forensics Essentials: Single-User Mode

Over the years, our training curriculum and instructors have provided Mac Forensics students with many ways to collect detailed forensic evidence from a Mac OS X system. But from time-to-time, our students ask us questions such as, “How do I get the date and time from a Mac without logging into the computer?” or, “Before I begin my examination, how do I determine if the computer is running OS X Lion or Snow Leopard?”


An examiner can quickly answer these and other basic Mac OS X system information questions, in a forensically sound manner, by booting the machine into ‘Single-User’ mode. A Mac in ‘Single-User’ mode operates from a bare-bones command-line interface. A forensic examiner may then issue a few simple commands to extract basic machine information without actually booting into the operating system.


Important Notes to Consider Before Booting into Single-User Mode


1 – To access Single-User mode, a live machine must be rebooted. Therefore, if an examiner comes upon an OS X machine that is running with encryption enabled (i.e. FileVault,) it may not be wise to reboot the machine, as the data is fully encrypted after the restart. A live data acquisition, using a tool such as MacQuisition, may be a better choice under these circumstances.

2 – A user may have disabled Single-User mode. If this is the case, the system may bypass Single-User mode and boot to the Mac OS X operating system (not good!). If this happens, IMMEDIATELY shut the computer down by pressing and holding the power button.

3 – A machine running OS X Lion (10.7.x) with FileVault 2 enabled is easily identifiable; the machine does not boot directly into Single-User mode. Instead, a FileVault 2 login screen with a password prompt appears.


Important Notes About Single-User Mode

Before booting a machine into Single-User mode, an examiner should understand two additional key points:


1 – In Single-User mode, devices, including the boot drive, are protected with read-only (essentially write-blocked) privileges,


2 – Commands issued in Single-User mode are issued as root, so some commands may circumvent read-only protection. Therefore, use caution and have a full understanding of each command before proceeding.


Booting Into Single-User Mode


1 – With the power off and the source system plugged into a power source (when possible), press the power button and immediately hold down the Option (alt) key. The EFI Boot screen (Startup Manager) appears.

2 – Select the machine’s main boot device to highlight it.

3 – Hold down the Command-S keys on the source computer’s keyboard, and select the arrow below the main boot device icon to begin the Single-User mode boot process.

4 – The source system boots into Single-User mode.  During the Single-User mode boot process, the boot sequence appears as white text on a black screen as it executes. The boot sequence completes and a root# shell prompt appears.

5 – DO NOT issue the fsck -fy command on a suspect device. While this is a helpful troubleshooting/repair command under normal circumstances, using it on a source device results in file modifications.

6 – DO NOT issue the mount -uw command on a source device. This causes a mounted file system to change from read-only status to read-write (not write protected!) status.

7 – DO NOT issue the exit command. This causes the machine to boot to the operating system (again, not good!) Instead, use the halt -ln (‘l’ rhymes with tell) command to shutdown the machine.


 Single-User mode prompt


Once again, if the Apple logo appears at any point during the boot process, IMMEDIATELY shut the computer down by pressing and holding the power button; the source system is attempting to boot to the OS X operating system and changes are written to the source device.


Issuing Commands In Single-User Mode

The following commands may be issued at the Single-User command prompt:

What: Display the system’s current local date and time with the local time zone (from the kernel clock, not the system clock)
Command: date

What: Display the system’s current local date and time in UTC (Coordinated Universal) time (from the kernel clock, not the system clock)
Command: date -u

What: Display the system’s Mac OS X version and other system software information
Command: system_profiler SPSoftwareDataType



What: Display the machine’s model, serial number, and other hardware information
Command: system_profiler SPHardwareDataType




If at any point the machine ‘hangs’ after a command is issued, type Control-C to return to the command prompt.


After all desired information is gathered, issue the halt -ln (‘l’ rhymes with tell) command to shutdown the computer.


You can learn more about acquiring data from a Mac computer here on our blog or by visiting BlackBag TV. For more information about MacQuisition, our 3-in-1 data acquisition solution, please visit our MacQuisition product page.


Please feel free to contact support at anytime as well with any additional questions or comments.

BlackBag Training Team
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