crash man page on Oracle

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CRASH(8)							      CRASH(8)

       crash - Analyze Linux crash dump data or a live system

       crash [OPTION]... NAMELIST MEMORY-IMAGE	  (dumpfile form)
       crash [OPTION]... [NAMELIST]		  (live system form)

       Crash is a tool for interactively analyzing the state of the Linux sys‐
       tem while it is running, or after a kernel crash	 has  occurred	and  a
       core  dump has been created by the netdump, diskdump, LKCD, kdump, xen‐
       dump or kvmdump facilities.  It is loosely based on the SVR4 UNIX crash
       command,	 but  has been significantly enhanced by completely merging it
       with the gdb(1) debugger. The marriage of the two effectively  combines
       the  kernel-specific  nature of the traditional UNIX crash utility with
       the source code level debugging capabilities of gdb(1).

       In the dumpfile form, both a NAMELIST and a MEMORY-IMAGE argument  must
       be  entered.   In  the  live system form, the NAMELIST argument must be
       entered if the kernel's vmlinux file is not located in  a  known	 loca‐
       tion,  such  as	the /usr/lib/debug/lib/modules/<kernel-version> direc‐

       The crash utility has also been extended to  support  the  analysis  of
       dumpfiles  generated  by	 a crash of the Xen hypervisor.	 In that case,
       the NAMELIST argument must be that of the xen-syms binary.  Live system
       analysis is not supported for the Xen hypervisor.

       The  crash  utility command set consists of common kernel core analysis
       tools such as kernel stack back traces of all  processes,  source  code
       disassembly,  formatted kernel structure and variable displays, virtual
       memory data, dumps of linked-lists, etc., along with  several  commands
       that  delve  deeper  into  specific kernel subsystems.  Appropriate gdb
       commands may also be entered, which in turn are passed on  to  the  gdb
       module  for  execution.	If desired, commands may be placed in either a
       $HOME/.crashrc file and/or in a .crashrc file in the current directory.
       During  initialization,	the  commands  in  $HOME/.crashrc are executed
       first, followed by those in the ./.crashrc file.

       The crash utility is designed to be independent of Linux version depen‐
       dencies.	 When new kernel source code impacts the correct functionality
       of crash and its command set, the utility will be updated to  recognize
       new kernel code changes, while maintaining backwards compatibility with
       earlier releases.

	      This is a pathname to an uncompressed kernel  image  (a  vmlinux
	      file),  or  a  Xen  hypervisor image (a xen-syms file) which has
	      been compiled with the "-g" option.  If using the dumpfile form,
	      a	 vmlinux  file	may be compressed in either gzip or bzip2 for‐

	      A kernel core dump file created by the netdump,  diskdump,  LKCD
	      kdump, xendump or kvmdump facilities.

	      If  a  MEMORY-IMAGE argument is not entered, the session will be
	      invoked on the live system, which typically requires root privi‐
	      leges  because of the device file used to access system RAM.  By
	      default, /dev/crash will be used if it exists.  If it  does  not
	      exist,  then  /dev/mem  will be used; but if the kernel has been
	      configured with CONFIG_STRICT_DEVMEM, then /proc/kcore  will  be
	      used.    It  is  permissible  to	explicitly  enter  /dev/crash,
	      /dev/mem or /proc/kcore.

	      If the NAMELIST file is not the  same  kernel  that  is  running
	      (live system form), or the kernel that was running when the sys‐
	      tem crashed (dumpfile form), then the	 file  of  the
	      original kernel should be entered on the command line.

       -h [option]
       --help [option]
	      Without  an option argument, display a crash usage help message.
	      If the option argument is a crash command name,  the  help  page
	      for  that	 command is displayed.	If it is the string "input", a
	      page describing the various crash command line input options  is
	      displayed.  If it is the string "output", a page describing com‐
	      mand line output options is displayed.   If  it  is  the	string
	      "all",  then  all	 of  the possible help messages are displayed.
	      After the help message is displayed, crash exits.

       -s     Silently proceed directly to the "crash>"	 prompt	 without  dis‐
	      playing  any  version,  GPL, or crash initialization data during
	      startup, and by default, runtime command output is not passed to
	      any scrolling command.

       -i file
	      Execute the command(s) contained in file prior to displaying the
	      "crash>" prompt for interactive user input.

       -d num Set the internal debug level.  The higher the number,  the  more
	      debugging data will be printed when crash initializes and runs.

       -S     Use /boot/ as the mapfile.

       -e vi | emacs
	      Set  the	readline(3)  command  line  editing  mode  to  "vi" or
	      "emacs".	The default editing mode is "vi".

       -f     Force the usage of a compressed vmlinux  file  if	 its  original
	      name does not start with "vmlinux".

       -k     Indicate that the NAMELIST file is an LKCD "Kerntypes" debuginfo

       -g [namelist]
	      Determine if a vmlinux or xen-syms namelist file contains debug‐
	      ging data.

       -t     Display the system-crash timestamp and exit.

       -L     Attempt  to lock all of its virtual address space into memory by
	      calling mlockall(MCL_CURRENT|MCL_FUTURE) during  initialization.
	      If  the  system  call fails, an error message will be displayed,
	      but the session continues.

       -c tty-device
	      Open the tty-device as the console used for debug messages.

       -p page-size
	      If a processor's page size cannot be determined by the dumpfile,
	      and the processor default cannot be used, use page-size.

       -m option=value
       --machdep option=value
	      Pass  an option and value pair to machine-dependent code.	 These
	      architecture-specific option/pairs should only  be  required  in
	      very rare circumstances:

		vm=orig	      (pre-2.6.11 virtual memory address ranges)
		vm=2.6.11     (2.6.11 and later virtual memory address ranges)
		vm=xen	      (Xen kernel virtual memory address ranges)
		vm=xen-rhel4  (RHEL4 Xen kernel virtual address ranges)
		vm=2.6.14     (4-level page tables)
		vm=4l	      (4-level page tables)

       -x     Automatically  load  extension  modules from a particular direc‐
	      tory.  If a directory is specified in the CRASH_EXTENSIONS shell
	      environment  variable, then that directory will be used.	Other‐
	      wise  /usr/lib64/crash/extensions	 (64-bit   architectures)   or
	      /usr/lib/crash/extensions	 (32-bit  architectures) will be used;
	      if they do not exist, then the ./extensions  directory  will  be

	      Track only the active task on each cpu.

	      Display  the  crash  binary's  build  date,  the	user ID of the
	      builder, the hostname of the machine where the build  was	 done,
	      the  target  architecture,  the version number, and the compiler

       --memory_module modname
	      Use the modname as an alternative kernel module to the  crash.ko
	      module that creates the /dev/crash device.

       --memory_device device
	      Use  device as an alternative device to the /dev/crash, /dev/mem
	      or /proc/kcore devices.

       --log dumpfile
	      Dump the contents of the kernel log buffer.  A  kernel  namelist
	      argument	is  not	 necessary,  but the dumpfile must contain the
	      VMCOREINFO data taken from the original /proc/vmcore ELF header.

	      Do  not  use  kallsyms-generated	symbol	information  contained
	      within kernel module object files.

	      Do not access or display any kernel module related information.

	      Do  not  attempt	to read configuration data that was built into
	      kernels configured with CONFIG_IKCONFIG.

	      Do not verify the validity of all structure member  offsets  and
	      structure sizes that it uses.

	      Do  not  initialize  the kernel's slab cache infrastructure, and
	      commands that use kmem_cache-related data will not work.

	      Do not use the registers from the ELF NT_PRSTATUS notes saved in
	      a compressed kdump header for backtraces.

	      Delay  the initialization of the kernel's slab cache infrastruc‐
	      ture until it is required by a run-time command.

	      Pass this flag to the embedded gdb module, which	will  override
	      its  two-stage  strategy	that it uses for reading symbol tables
	      from the NAMELIST.

       --smp  Specify that the system being analyzed is an SMP kernel.

	      Display the version of the crash utility,	 the  version  of  the
	      embedded gdb module, GPL information, and copyright notices.

       --cpus number
	      Specify the number of cpus in the SMP system being analyzed.

       --osrelease dumpfile
	      Display  the  OSRELEASE  vmcoreinfo string from a kdump dumpfile

	      Force the session to be that of a Xen hypervisor.

       --p2m_mfn pfn
	      When a Xen Hypervisor or its dom0 kernel crashes,	 the  dumpfile
	      is typically analyzed with either the Xen hypervisor or the dom0
	      kernel.  It is also possible to analyze any of  the  guest  domU
	      kernels  if the pfn_to_mfn_list_list pfn value of the guest ker‐
	      nel is passed on the command line along with  its	 NAMELIST  and
	      the dumpfile.

       --xen_phys_start physical-address
	      Supply  the  base	 physical address of the Xen hypervisor's text
	      and static data for older xendump dumpfiles that	did  not  pass
	      that information in the dumpfile header.

	      If  a  kdump dumpfile has been filtered to exclude various types
	      of non-essential pages, any attempt  to  read  them  will	 fail.
	      With  this flag, reads from any of those pages will return zero-
	      filled memory.

	      Do not attempt to find the task that was running when the kernel
	      crashed.	 Set the initial context to that of the "swapper" task
	      on cpu 0.

       --more Use /bin/more as the command  output  scroller,  overriding  the
	      default  of  /usr/bin/less and any settings in either ./.crashrc
	      or $HOME/.crashrc.

       --less Use /usr/bin/less as the command output scroller, overriding any
	      settings in either ./.crashrc or $HOME/.crashrc.

       --hex  Set  the	default	 command  output  radix	 to 16, overriding the
	      default radix of 10, and any radix settings in either ./.crashrc
	      or $HOME/.crashrc.

       --dec  Set the default command output radix to 10, overriding any radix
	      settings in either ./.crashrc or	$HOME/.crashrc.	 This  is  the
	      default radix setting.

	      Use  the	output	paging command defined in the CRASHPAGER shell
	      environment  variable,  overriding  any	settings   in	either
	      ./.crashrc or $HOME/.crashrc.

	      Do not pass run-time command output to any scrolling command.

	      Do not strip cloned kernel text symbol names.

	      Do   not	execute	 the  commands	in  either  $HOME/.crashrc  or

       --mod directory
	      When loading the debuginfo data of kernel modules with  the  mod
	      -S  command,  search for their object files in directory instead
	      of in the standard location.

       --reloc size
	      When analyzing live x86 kernels that were configured with a CON‐
	      FIG_PHYSICAL_START  value	 that is larger than its CONFIG_PHYSI‐
	      CAL_ALIGN value, then it will be necessary to enter a relocation
	      size equal to the difference between the two values.

	      Bring  up a session that is restricted to the log, dis, rd, sym,
	      eval, set and exit commands.  This option may provide a  way  to
	      extract some minimal/quick information from a corrupted or trun‐
	      cated dumpfile, or in situations where one of the several kernel
	      subsystem initialization routines would abort the crash session.

       --kvmhost [32|64]
	      When  examining an x86 KVM guest dumpfile, this option specifies
	      that the KVM host that created the dumpfile was an x86  (32-bit)
	      or  an  x86_64  (64-bit)	machine,  overriding the automatically
	      determined value.

       --kvmio <size>
	      override the automatically-calculated KVM guest I/O hole size.

       Each crash command generally falls into	one  of	 the  following	 cate‐

       Symbolic display
	      Displays	of  kernel text/data, which take full advantage of the
	      power of gdb to format and display data structures symbolically.

       System state
	      The majority of crash commands consist  of  a  set  of  "kernel-
	      aware" commands, which delve into various kernel subsystems on a
	      system-wide or per-task basis.

       Utility functions
	      A set of useful helper commands serving various  purposes,  some
	      simple, others quite powerful.

       Session control
	      Commands that control the crash session itself.

       The  following  alphabetical list consists of a very simple overview of
       each crash command.  However, since individual commands often have sev‐
       eral  options  resulting	 in significantly different output, it is sug‐
       gested that the full description of each command be viewed by executing
       crash -h <command>,  or	during a crash session by simply entering help

       *      "pointer to" is shorthand for either the struct  or  union  com‐
	      mands.  It displays the contents of a kernel structure or union.

       alias  creates a single-word alias for a command.

       ascii  displays	an  ascii chart or translates a numeric value into its
	      ascii components.

       bt     displays a task's kernel-stack backtrace.	 If it is given the -a
	      option,  it displays the stack traces of the active tasks on all
	      CPUs.  It is often used with the foreach command to display  the
	      backtraces of all tasks with one command.

       btop   translates a byte value (physical offset) to its page number.

       dev    displays	data concerning the character and block device assign‐
	      ments, I/O port usage, I/O memory usage, and PCI device data.

       dis    disassembles memory, either  entire  kernel  functions,  from  a
	      location	for  a	specified  number of instructions, or from the
	      start of a function up to a specified memory location.

       eval   evaluates an expression or numeric type and displays the	result
	      in hexadecimal, decimal, octal and binary.

       exit   causes crash to exit.

       extend dynamically  loads or unloads crash shared object extension mod‐

       files  displays information about open files in a context.

	      repeats a specified command for the specified (or all) tasks  in
	      the system.

       fuser  displays the tasks using the specified file or socket.

       gdb    passes  its  argument  to the embedded gdb module.  It is useful
	      for executing gdb commands that have the same name as crash com‐

       help   alone  displays the command menu; if followed by a command name,
	      a full description of a command, its options, and	 examples  are
	      displayed.  Its output is far more complete and useful than this
	      man page.

       ipcs   displays data about the System V IPC facilities.

       irq    displays data concerning interrupt request numbers  and  bottom-
	      half interrupt handling.

       kmem   displays information about the use of kernel memory.

       list   displays the contents of a linked list.

       log    displays the kernel log_buf contents in chronological order.

       mach   displays data specific to the machine type.

       mod    displays	information  about the currently installed kernel mod‐
	      ules, or adds or deletes symbolic or debugging information about
	      specified kernel modules.

       mount  displays information about the currently-mounted filesystems.

       net    display various network related data.

       p      passes  its  arguments to the gdb "print" command for evaluation
	      and display.

       ps     displays process status for specified, or all, processes in  the

       pte    translates  the  hexadecimal contents of a PTE into its physical
	      page address and page bit settings.

       ptob   translates a page frame number to its byte value.

       ptov   translates a hexadecimal physical address into a kernel  virtual

       q      is an alias for the "exit" command.

       rd     displays	the  contents  of memory, with the output formatted in
	      several different manners.

       repeat repeats a command indefinitely, optionally delaying a given num‐
	      ber of seconds between each command execution.

       runq   displays the tasks on the run queue.

       search searches a range of user or kernel memory space for given value.

       set    either  sets a new context, or gets the current context for dis‐

       sig    displays signal-handling data of one or more tasks.

       struct displays either a structure definition or the contents of a ker‐
	      nel structure at a specified address.

       swap   displays information about each configured swap device.

       sym    translates  a  symbol to its virtual address, or a static kernel
	      virtual address to its symbol  --	 or  to	 a  symbol-plus-offset
	      value, if appropriate.

       sys    displays system-specific data.

       task   displays the contents of a task_struct.

       tree   displays the contents of a red-black tree or a radix tree.

       timer  displays	the  timer  queue entries, both old- and new-style, in
	      chronological order.

       union  is similar to the struct command, except that it works on kernel

       vm     displays basic virtual memory information of a context.

       vtop   translates  a  user  or  kernel  virtual address to its physical

       waitq  walks the wait queue list displaying the tasks which are blocked
	      on the specified wait queue.

       whatis displays	the  definition	 of  structures,  unions,  typedefs or
	      text/data symbols.

       wr     modifies the contents of memory on a live system.	 It  can  only
	      be used if /dev/mem is the device file being used to access sys‐
	      tem RAM, and should obviously be used with great care.

       When crash is invoked with a Xen hypervisor binary as the NAMELIST, the
       command	set is slightly modified.  The *, alias, ascii, bt, dis, eval,
       exit, extend, gdb, help, list, log, p, pte, rd,	repeat,	 search,  set,
       struct,	sym,  sys,  union,  whatis,  wr and q commands are the same as
       above.  The following commands are specific to the Xen hypervisor:

       domain displays the contents of the domain structure for	 selected,  or
	      all, domains.

       doms   displays domain status for selected, or all, domains.

	      displays Xen dump information for selected, or all, cpus.

       pcpus  displays physical cpu information for selected, or all, cpus.

       vcpus  displays vcpu status for selected, or all, vcpus.

	      Initialization  commands.	 The file can be located in the user's
	      HOME directory and/or the current directory.  Commands found  in
	      the  .crashrc  file  in  the  HOME directory are executed before
	      those in the current directory's .crashrc file.

       EDITOR Command input is read using readline(3).	If EDITOR  is  set  to
	      emacs  or	 vi  then suitable keybindings are used.  If EDITOR is
	      not set, then vi is used.	 This can be overridden by set	vi  or
	      set emacs commands located in a .crashrc file, or by entering -e
	      emacs on the crash command line.

	      If CRASHPAGER is set, its value is used as the name of the  pro‐
	      gram to which command output will be sent.  If not, then command
	      output is sent to /usr/bin/less -E -X by default.

	      Specifies an alternative directory tree  to  search  for	kernel
	      module object files.

	      Specifies	 a directory containing extension modules that will be
	      loaded automatically if the -x command line option is used.

       If crash does not work, look for a newer version: kernel evolution fre‐
       quently makes crash updates necessary.

       The command set scroll off will cause output to be sent directly to the
       terminal rather than through a paging program.	This  is  useful,  for
       example, if you are running crash in a window of emacs.

       Dave Anderson <> wrote crash.

       Jay  Fenlason  <>  and  Dave Anderson <anderson@red‐> wrote this man page.

       The help command within crash provides more complete and accurate docu‐
       mentation than this man page. - the home page of the crash utility.

       netdump(8), gdb(1)


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