Editing Kernel panic (section)

==Causes==
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. If the system is in an unstable state, rather than risking security breaches and data corruption, the operating system stops in order to prevent further damage, which helps to facilitate diagnosis of the error and may restart automatically.<ref name="Hancock2002">{{cite book|author=Steven M. Hancock|title=Tru64 UNIX troubleshooting: diagnosing and correcting system problems|url=https://books.google.com/books?id=wh438GgIJtEC&pg=PA119|access-date=May 3, 2011|date=November 22, 2002|publisher=Digital Press|isbn=978-1-55558-274-6|pages=119–126}}</ref>

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.<ref name="Jang2006">{{cite book|author=Michael Jang|title=Linux annoyances for geeks|url=https://books.google.com/books?id=cNGbObmg6IwC&pg=PA267|access-date=April 29, 2011|year=2006|publisher=O'Reilly Media, Inc.|isbn=978-0-596-00801-7|pages=267–274}}</ref> 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]].<ref name="Pogue2009">{{cite book|author=David Pogue|title=Switching to the Mac: The Missing Manual, Snow Leopard Edition|url=https://books.google.com/books?id=SjuiTv7DepEC&pg=PA589|access-date=May 4, 2011|date=December 17, 2009|publisher=O'Reilly Media, Inc.|isbn=978-0-596-80425-1|page=589}}</ref> A kernel may also go into <code>panic()</code> if it is unable to locate a [[root file system]].<ref name="Kroah-Hartman2007">{{cite book|author=Greg Kroah-Hartman|title=Linux kernel in a nutshell|url=https://books.google.com/books?id=1rFLGKO0dywC&pg=PA59|access-date=May 3, 2011|year=2007|publisher=O'Reilly Media, Inc.|isbn=978-0-596-10079-7|page=59}}</ref> 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.<ref name="Mauerer2008">{{cite book|author=Wolfgang Mauerer|title=Professional Linux Kernel Architecture|url=https://books.google.com/books?id=e8BbHxVhzFAC&pg=PA1238|access-date=May 3, 2011|date=September 26, 2008|publisher=John Wiley and Sons|isbn=978-0-470-34343-2|pages=1238–1239|archive-date=April 1, 2024|archive-url=https://web.archive.org/web/20240401232239/https://books.google.com/books?id=e8BbHxVhzFAC&pg=PA1238|url-status=live}}</ref>

The following is an implementation of the Linux kernel final initialization in <code>kernel_init()</code>:<ref name="lxr, init/main.c">{{cite web |url=http://lxr.linux.no/linux+v3.10/init/main.c#L811 |title=linux/init/main.c |website=[[LXR Cross Referencer]] |archive-url=https://web.archive.org/web/20221006174048/http://lxr.linux.no/linux+v3.10/init/main.c#L811 |archive-date=October 6, 2022 |url-status=live}}</ref>
<syntaxhighlight lang="c">
static int __ref kernel_init(void *unused)
{

         ...

        /*
         * We try each of these until one succeeds.
         *
         * The Bourne shell can be used instead of init if we are
         * trying to recover a really broken machine.
         */
        if (execute_command) {
                if (!run_init_process(execute_command))
                        return 0;
                pr_err("Failed to execute %s.  Attempting defaults...\n",
                        execute_command);
        }
        if (!run_init_process("/sbin/init") ||
            !run_init_process("/etc/init") ||
            !run_init_process("/bin/init") ||
            !run_init_process("/bin/sh"))
                return 0;

        panic("No init found.  Try passing init= option to kernel. "
              "See Linux Documentation/init.txt for guidance.");
}
 </syntaxhighlight>