Mac Kernel Panic Screen

A kernel panic message from a Linux system

When you get a Kernel Panic on OS X, the screen darkens and you see a multilingual message that tells you to restart your computer. So, this made me wonder – what the heck causes this? Much like a Blue Screen of Death on Windows, this could be indicative of a software problem, a hardware problem, or a conflict of hardware and software. Similar to this fake kernel panic app, the Kernel Panic Screensaver draws what looks just like a real kernel panic on the Mac display, leading yourself (or the unsuspecting observer) to think a Mac has suffered from a total system failure. 'Kernel panic' is a type of problem, which sounds very serious, but it might be easier to resolve than you think. It usually concerns users of UNIX-based operating systems like Linux and macOS. In short, it is very similar to Windows' Blue Screen of Death (BSOD.).

Kernel panic in Ubuntu 13.04 (Linux 3.8) in Oracle VM VirtualBox

A kernel panic (sometimes abbreviated as KP[1]) is a safety measure taken by an operating system's kernel upon detecting an internal fatal error in which either it is unable to safely recover or continuing to run the system would have a higher risk of major data loss. The term is largely specific to Unix and Unix-like systems. For Microsoft Windows operating systems the equivalent term is 'Stop error', resulting in a bug check[2] screen that presents the bug check code on a blue background in early versions of Windows (colloquially known as a 'Blue Screen of Death' or BSoD), or on a green background on the Xbox One platform as well as in Windows 10 preview builds.[3]

The kernel routines that handle panics, known as panic() in AT&T-derived and BSD Unix source code, are generally designed to output an error message to the console, dump an image of kernel memory to disk for post-mortem debugging, and then either wait for the system to be manually rebooted, or initiate an automatic reboot.[4] The information provided is of a highly technical nature and aims to assist a system administrator or software developer in diagnosing the problem. Kernel panics can also be caused by errors originating outside kernel space. For example, many Unix operating systems panic if the init process, which runs in user space, terminates.[5][6]

History[edit]

The Unix kernel maintains internal consistency and runtime correctness with assertions as the fault detection mechanism. The basic assumption is that the hardware and the software should perform correctly and a failure of an assertion results in a panic, i.e. a voluntary halt to all system activity.[7] The kernel panic was introduced in an early version of Unix and demonstrated a major difference between the design philosophies of Unix and its predecessor Multics. Multics developer Tom van Vleck recalls a discussion of this change with Unix developer Dennis Ritchie:

I remarked to Dennis that easily half the code I was writing in Multics was error recovery code. He said, 'We left all that stuff out. If there's an error, we have this routine called panic, and when it is called, the machine crashes, and you holler down the hall, 'Hey, reboot it.'[8]

The original panic() function was essentially unchanged from Fifth Edition UNIX to the VAX-based UNIX 32V and output only an error message with no other information, then dropped the system into an endless idle loop.

Source code of panic() function in V6 UNIX:[9]

As the Unix codebase was enhanced, the panic() function was also enhanced to dump various forms of debugging information to the console.

Causes[edit]

A panic may occur as a result of a hardware failure or a software bug in the operating system. In many cases, the operating system is capable of continued operation after an error has occurred. However, the system is in an unstable state and rather than risking security breaches and data corruption, the operating system stops to prevent further damage and facilitate diagnosis of the error and, in usual cases, restart.[10]

After recompiling a kernel binary image from source code, a kernel panic while booting the resulting kernel is a common problem if the kernel was not correctly configured, compiled or installed.[11] Add-on hardware or malfunctioning RAM could also be sources of fatal kernel errors during start up, due to incompatibility with the OS or a missing device driver.[12] A kernel may also go into panic() if it is unable to locate a root file system.[13] During the final stages of kernel userspace initialization, a panic is typically triggered if the spawning of init fails. A panic might also be triggered if the init process terminates, as the system would then be unusable.[14]

Mac

The following is an implementation of the Linux kernel final initialization in kernel_init():[15]

Operating system specifics[edit]

Linux[edit]

Imac Kernel Panic Fix

Kernel panic as seen on an iKVM console

Kernel panics appear in Linux like in other Unix-like systems, but they can also generate another kind of error condition, known as a kernel oops.[16] In this case, the kernel normally continues to run after killing the offending process. As an oops could cause some subsystems or resources to become unavailable, they can later lead to a full kernel panic.

Hackintosh Kernel Panic

On Linux, a kernel panic causes keyboard LEDs to blink as a visual indication of a critical condition.[17]

macOS[edit]

When a kernel panic occurs in Mac OS X 10.2 through 10.7, the computer displays a multilingual message informing the user that they need to reboot the system.[18] Prior to 10.2, a more traditional Unix-style panic message was displayed; in 10.8 and later, the computer automatically reboots and displays a message after the restart. The format of the message varies from version to version:[19]

  • 10.0–10.1: The system displays text on the screen, giving details about the error, and becomes unresponsive.
  • 10.2: Rolls down a black transparent curtain then displays a message on a white background informing the user that they should restart the computer. The message is shown in English, French, German and Japanese.
  • 10.3–10.5: The kernel panic is almost the same as version 10.2 but the background of the error screen is black.
  • 10.6–10.7-10.8: The text has been revised and now includes a Spanish translation.
  • 10.9 and later: The computer becomes unresponsive before it immediately reboots. When the computer starts back up, it shows a warning message for a few seconds about the computer restarting because of a kernel panic, and then the computer restarts back up. The message now includes a Chinese translation.

Sometimes when there are five or more kernel panics within three minutes of the first one, the Mac will display a prohibitory sign for 30 seconds, and then shut down (this is known as a 'recurring kernel panic').

In all versions above 10.2, the text is superimposed on a standby symbol and is not full screen. Debugging information is saved in NVRAM and written to a log file on reboot. In 10.7 there is a feature to automatically restart after a kernel panic. In some cases, on 10.2 and later, white text detailing the error may appear in addition to the standby symbol.

  • Mac OS X 10.0–10.1 kernel panic

  • Mac OS X 10.2 kernel panic

  • Mac OS X 10.3–10.5 kernel panic

  • Mac OS X 10.6 and 10.7 kernel panic

  • Message shown after the computer restarts because of a kernel panic in OS X 10.8 and later versions

See also[edit]

Wikimedia Commons has media related to Kernel panic.

References[edit]

  1. ^'KP - Kernel Panic (Linux) AcronymFinder'. www.acronymfinder.com. Retrieved January 6, 2016.
  2. ^'Bug Checks (Blue Screens)'. Hardware Dev Center - Microsoft.
  3. ^Hoffman, Chris. 'Did You Know Windows 10 Has a Green Screen of Death?'. How-To Geek. Retrieved June 4, 2020.
  4. ^'FreeBSD 11.0 - man page for panic (freebsd section 9) - Unix & Linux Commands'. www.unix.com.
  5. ^'boot failure-init died - Unix Linux Forums - HP-UX'. www.unix.com.
  6. ^Randolph J. Herber (September 1, 1999). 'Re: PANIC: init died'. Newsgroup: comp.sys.sgi.admin.
  7. ^Daniel P. Siewiorek; Robert S. Swarz (1998). Reliable computer systems: design and evaluation. A K Peters, Ltd. p. 622. ISBN978-1-56881-092-8. Retrieved May 6, 2011.
  8. ^'Unix and Multics'. www.multicians.org.
  9. ^Source code /usr/sys/ken/prf.c from V6 UNIX
  10. ^Steven M. Hancock (November 22, 2002). Tru64 UNIX troubleshooting: diagnosing and correcting system problemsHP Technologies SeriesITPro collection. Digital Press. pp. 119–126. ISBN978-1-55558-274-6. Retrieved May 3, 2011.
  11. ^Michael Jang (2006). Linux annoyances for geeks. O'Reilly Media, Inc. pp. 267–274. ISBN978-0-596-00801-7. Retrieved April 29, 2011.
  12. ^David Pogue (December 17, 2009). Switching to the Mac: The Missing Manual, Snow Leopard Edition. O'Reilly Media, Inc. p. 589. ISBN978-0-596-80425-1. Retrieved May 4, 2011.
  13. ^Greg Kroah-Hartman (2007). Linux kernel in a nutshell. O'Reilly Media, Inc. p. 59. ISBN978-0-596-10079-7. Retrieved May 3, 2011.
  14. ^Wolfgang Mauerer (September 26, 2008). Professional Linux Kernel Architecture. John Wiley and Sons. pp. 1238–1239. ISBN978-0-470-34343-2. Retrieved May 3, 2011.
  15. ^linux/init/main.c, LXR Cross Referencer
  16. ^'Linux Device Drivers, Chapter 4'(PDF).
  17. ^James Kirkland; David Carmichael; Christopher L. Tinker; Gregory L. Tinker (May 2006). Linux Troubleshooting for System Administrators and Power Users. Prentice Hall. p. 62. ISBN9780132797399. Retrieved February 5, 2016.
  18. ^'OS X: About kernel panics - Apple Support'. support.apple.com.
  19. ^'A New Screen of Death for Mac OS X'. OSXBook.com.
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