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CRASH(8)							      CRASH(8)

NAME
       crash - UNIX system failures

DESCRIPTION
       This  section  explains	what happens when the system crashes and (very
       briefly) how to analyze crash dumps.

       When the system crashes voluntarily it prints a message of the form

	      panic: why i gave up the ghost

       on the console, takes a dump on a mass  storage	peripheral,  and  then
       invokes	an  automatic reboot procedure as described in reboot(8).  (If
       auto-reboot is disabled on the front panel of the  machine  the	system
       will  simply halt at this point.)  Unless some unexpected inconsistency
       is encountered in the state of the file	systems	 due  to  hardware  or
       software failure, the system will then resume multi-user operations.

       The system has a large number of internal consistency checks; if one of
       these fails, then it will panic with a very  short  message  indicating
       which one failed.  In many instances, this will be the name of the rou‐
       tine which detected the error, or a two-word description of the	incon‐
       sistency.  A full understanding of most panic messages requires perusal
       of the source code for the system.

       The most common cause of system failures is hardware failure, which can
       reflect itself in different ways.  Here are the messages which are most
       likely, with some hints as to causes.  Left unstated in	all  cases  is
       the possibility that hardware or software error produced the message in
       some unexpected way.

       iinit  This cryptic panic message results from a failure to  mount  the
	      root  filesystem	during the bootstrap process.  Either the root
	      filesystem has been corrupted, or the system  is	attempting  to
	      use  the wrong device as root filesystem.	 Usually, an alternate
	      copy of the system binary or an alternate root filesystem can be
	      used to bring up the system to investigate.

       Can't exec /sbin/init
	      This is not a panic message, as reboots are likely to be futile.
	      Late in the bootstrap procedure, the system was unable to locate
	      and  execute  the	 initialization	 process,  init(8).   The root
	      filesystem is incorrect or has been corrupted, or	 the  mode  or
	      type of /sbin/init forbids execution.

       IO err in push
       hard IO err in swap
	      The  system  encountered	an error trying to write to the paging
	      device or an error in reading critical information from  a  disk
	      drive.   The  offending  disk should be fixed if it is broken or
	      unreliable.

       realloccg: bad optim
       ialloc: dup alloc
       alloccgblk: cyl groups corrupted
       ialloccg: map corrupted
       free: freeing free block
       free: freeing free frag
       ifree: freeing free inode
       alloccg: map corrupted
	      These panic messages are among those that may be	produced  when
	      filesystem  inconsistencies are detected.	 The problem generally
	      results from a failure to repair	damaged	 filesystems  after  a
	      crash,  hardware	failures,  or  other condition that should not
	      normally occur.  A filesystem check will	normally  correct  the
	      problem.

       timeout table overflow
	      This  really  shouldn't be a panic, but until the data structure
	      involved is made to be extensible, running out of entries causes
	      a crash.	If this happens, make the timeout table bigger.

       KSP not valid
       SBI fault
       CHM? in kernel
	      These  indicate  either  a  serious  bug	in the system or, more
	      often, a glitch or failing hardware.  If SBI faults recur, check
	      out  the	hardware  or  call field service.  If the other faults
	      recur, there is likely a bug somewhere in the  system,  although
	      these can be caused by a flakey processor.  Run processor micro‐
	      diagnostics.

       machine check %x:
	      description

	  machine dependent machine-check information
	      Machine checks are different on each type of CPU.	 Most  of  the
	      internal	processor registers are saved at the time of the fault
	      and are printed on the console.  For most processors,  there  is
	      one  line that summarizes the type of machine check.  Often, the
	      nature of the problem is apparent from this messaage and/or  the
	      contents	of key registers.  The VAX Hardware Handbook should be
	      consulted, and, if necessary, your friendly field service people
	      should be informed of the problem.

       trap type %d, code=%x, pc=%x
	      A unexpected trap has occurred within the system; the trap types
	      are:

	      0	   reserved addressing fault
	      1	   privileged instruction fault
	      2	   reserved operand fault
	      3	   bpt instruction fault
	      4	   xfc instruction fault
	      5	   system call trap
	      6	   arithmetic trap
	      7	   ast delivery trap
	      8	   segmentation fault
	      9	   protection fault
	      10   trace trap
	      11   compatibility mode fault
	      12   page fault
	      13   page table fault

	      The favorite trap types in system crashes are trap types	8  and
	      9,  indicating  a	 wild  reference.   The code is the referenced
	      address, and the pc at the time of the fault is printed.	 These
	      problems	tend  to be easy to track down if they are kernel bugs
	      since the processor stops cold, but random  flakiness  seems  to
	      cause  this  sometimes.	The debugger can be used to locate the
	      instruction and subroutine corresponding to the  PC  value.   If
	      that  is insufficient to suggest the nature of the problem, more
	      detailed examination of the system status at  the	 time  of  the
	      trap usually can produce an explanation.

       init died
	      The system initialization process has exited.  This is bad news,
	      as no new users will then be able to log in.  Rebooting  is  the
	      only fix, so the system just does it right away.

       out of mbufs: map full
	      The  network has exhausted its private page map for network buf‐
	      fers.  This usually indicates that buffers are being  lost,  and
	      rather than allow the system to slowly degrade, it reboots imme‐
	      diately.	The map may be made larger if necessary.

       That completes the list of panic types you are likely to see.

       When the system crashes it writes (or at least attempts	to  write)  an
       image  of memory into the back end of the dump device, usually the same
       as the primary swap area.  After the system is  rebooted,  the  program
       savecore(8)  runs  and preserves a copy of this core image and the cur‐
       rent  system  in	 a  specified  directory  for  later   perusal.	   See
       savecore(8) for details.

       To  analyze  a dump you should begin by running adb(1) with the -k flag
       on the system load image and core dump.	 If  the  core	image  is  the
       result  of a panic, the panic message is printed.  Normally the command
       ``$c'' will provide a stack trace from the point of the crash and  this
       will provide a clue as to what went wrong.  For more detail see ``Using
       ADB to Debug the UNIX Kernel''.

SEE ALSO
       adb(1), reboot(8)
       VAX 11/780 System Maintenance Guide and VAX Hardware Handbook for  more
       information about machine checks.
       Using ADB to Debug the UNIX Kernel

4th Berkeley Distribution	 June 5, 1993			      CRASH(8)
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