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    Command:

    crash

    
    
    

    SYNOPSIS

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

    DESCRIPTION

           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-
           tory.
    
           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.
    
    
    

    OPTIONS

           NAMELIST
                  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-
                  mats.
    
           MEMORY-IMAGE
                  A kernel core dump file created by the netdump,  diskdump,  LKCD
                  tem crashed (dumpfile form), then the  System.map  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.  After the  help  message
                  is displayed, crash exits.
    
           -s     Proceed  directly  to the "crash>" prompt without displaying any
                  version, GPL, or crash initialization data during startup.
    
           -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/System.map 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.
    
           -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
                  IA64:
                    phys_start=<physical-address>
                    init_stack_size=<size>
                    vm=4l         (4-level page tables)
                  ARM:
                    physbase=<physical-address>
    
           -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
                  used.
    
           --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.
    
           --no_kallsyms
                  Do  not  use  kallsyms-generated  symbol  information  contained
                  within kernel module object files.
    
           --no_modules
                  Do  not access or display any kernel module related information.
    
           --no_ikconf
                  Do not attempt to read configuration data that  was  built  into
                  kernels configured with CONFIG_IKCONFIG.
    
           --no_data_debug
                  Do  not  verify the validity of all structure member offsets and
                  structure sizes that it uses.
    
           --no_kmem_cache
                  Do not initialize the kernel's slab  cache  infrastructure,  and
                  commands that use kmem_cache-related data will not work.
    
           --no_elf_notes
                  Do not use the registers from the ELF NT_PRSTATUS notes saved in
                  a compressed kdump header for backtraces.
    
           --kmem_cache_delay
                  Delay the initialization of the kernel's slab cache  infrastruc-
                  ture until it is required by a run-time command.
    
           --readnow
                  Pass  this  flag to the embedded gdb module, which will override
                  Display the OSRELEASE vmcoreinfo string from  a  kdump  dumpfile
                  header.
    
           --hyper
                  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.
    
           --zero_excluded
                  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.
    
           --no_panic
                  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.
    
           --CRASHPAGER
                  Use the output paging command defined in  the  CRASHPAGER  shell
                  environment   variable,   overriding   any  settings  in  either
                  ./.crashrc or $HOME/.crashrc.
    
           --no_scroll
                  Do not pass run-time command output to any scrolling command.
    
           --no_crashrc
                  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
    
           --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.
    
    
    

    COMMANDS

           Each crash command generally falls into  one  of  the  following  cate-
           gories:
    
           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
           command.
    
           *      "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.
    
    
           files  displays information about open files in a context.
    
           foreach
                  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-
                  mands.
    
           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.
    
           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
                  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.
           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.
    
           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 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.
    
           dumpinfo
                  displays Xen dump information for selected, or all, cpus.
    
           pcpus  displays physical cpu information for selected, or all, cpus.
    
                  emacs on the crash command line.
    
           CRASHPAGER
                  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.
    
           CRASH_MODULE_PATH
                  Specifies  an  alternative  directory  tree to search for kernel
                  module object files.
    
           CRASH_EXTENSIONS
                  Specifies a directory containing extension modules that will  be
                  loaded automatically if the -x command line option is used.
    
    
    

    NOTES

           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.
    
    
    

    AUTHOR

           Dave Anderson <anderson@redhat.com> wrote crash.
    
           Jay Fenlason <fenlason@redhat.com>  and  Dave  Anderson  <anderson@red-
           hat.com> wrote this man page.
    
    
    

    SEE ALSO

           The help command within crash provides more complete and accurate docu-
           mentation than this man page.
    
           http://people.redhat.com/anderson - the home page of the crash utility.
    
           netdump(8), gdb(1)
    
                                                                          CRASH(8)
    
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