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CRASH(8)                                                              CRASH(8)

       crash - Analyze Linux crash dump data or a live system

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

       Crash  is a tool for interactively analyzing the state of the Linux system while it is running, or after a ker-
       nel crash has occurred and a core dump has been created by the netdump, diskdump, LKCD, kdump, xendump or  kvm-
       dump  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-spe-
       cific 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 location, such as
       the /usr/lib/debug/lib/modules/<kernel-version> directory.

       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 direc-
       tory.   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 dependencies.  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 formats.

              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  typi-
              cally  requires  root  privileges  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 ker-
              nel  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.

              An @ADDRESS value must be appended to the MEMORY-IMAGE if the dumpfile is a raw RAM dumpfile that has no
              header  information  describing  the  file contents.  Multiple MEMORY-IMAGE@ADDRESS ordered pairs may be
              entered, with each dumpfile containing a contiguous block of RAM, where the ADDRESS value is the  physi-
              cal  start address of the block expressed in hexadecimal.  The physical address value(s) will be used to
              create a temporary ELF header in /var/tmp, which will only exist during the crash session.

              If the NAMELIST file is not the same kernel that is running (live system form), or the kernel  that  was
              running  when the system 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  com-
              mand  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  command line output options is displayed.  If it is the string "all", then all of the possi-
              ble help messages are displayed.  After the help message is displayed, crash exits.

       -s     Silently proceed directly to the "crash>" prompt without displaying any version, GPL, or crash  initial-
              ization  data during startup, and by default, runtime command output is not passed to any scrolling com-

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

       -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 file.

       -g [namelist]
              Determine if a vmlinux or xen-syms namelist file contains debugging 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

       -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.

       -o filename
              Only  used with the MEMORY-IMAGE@ADDRESS format for raw RAM dumpfiles, specifies a filename of a new ELF
              vmcore that will be created and used as the dumpfile.  It will be saved to allow future use as  a  stan-
              dalone vmcore, replacing the original raw RAM dumpfile.

       -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 directory.  If a directory is  specified  in  the
              CRASH_EXTENSIONS   shell   environment   variable,   then   that  directory  will  be  used.   Otherwise
              /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 used.

              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 version.

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

       --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 dump-
              file 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 back-

              Delay the initialization of the kernel's slab cache infrastructure until it is required  by  a  run-time

              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 header.

              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 kernel 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  dump-
              files that did not pass that information in the dumpfile header.

              If  the  makedumpfile(8)  facility  has filtered a compressed kdump dumpfile to exclude various types of
              non-essential pages, or has marked a compressed or ELF kdump dumpfile as incomplete due to an ENOSPC  or
              other  error  during  its  creation, any attempt to read missing pages 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

       --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 set-
              tings 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 ./.crashrc.

       --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.

       --kaslr offset|auto
              If  an x86_64 kernel was configured with CONFIG_RANDOMIZE_BASE, the offset value is equal to the differ-
              ence between the symbol values compiled into the vmlinux file and their relocated KASLR values.  If  set
              to auto, the KASLR offset value will be automatically calculated.

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

       --hash count
              Set the number of internal hash queue heads used for list gathering and verification.  The default count
              is 32768.

              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 truncated dump-
              file, 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 dump-
              file 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.

       --offline [show|hide]
              Show or hide command output that is related to offline cpus.  The default setting is show.

       Each crash command generally falls into one of the following categories:

       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 indi-
       vidual  commands  often  have several options resulting in significantly different output, it is suggested that
       the full description of each command be viewed by executing crash -h <command>, or during a  crash  session  by
       simply entering help command.

       *      "pointer to" is shorthand for either the struct or union commands.  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 assignments, 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 instruc-
              tions, 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

       exit   causes crash to exit.

       extend dynamically loads or unloads crash shared object extension modules.

       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 commands.

       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 modules, or adds or deletes symbolic or debug-
              ging 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 system.

       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 address.

       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 number of seconds between each command  exe-

       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 display.

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

       struct displays either a structure definition or the contents of a kernel 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 unions.

       vm     displays basic virtual memory information of a context.

       vtop   translates a user or kernel virtual address to its physical address.

       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 system 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 direc-
              tory.   Commands  found in the .crashrc file in the HOME directory are executed before those in the cur-
              rent 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 program 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 frequently 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 <> wrote this man page.

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

       netdump(8), gdb(1), makedumpfile(8)