crash(8) — Linux manual page


CRASH(8)                   System Manager's Manual                  CRASH(8)

NAME         top

       crash - Analyze Linux crash dump data or a live system

SYNOPSIS         top

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

DESCRIPTION         top

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

       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
       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.

OPTIONS         top

              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

              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
              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 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.

              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
              physical 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 a raw RAM dumpile represents a live
              memory source, such as that specified by the QEMU mem-path
              argument of a memory-backend-file object, then "live:" must be
              prepended to the MEMORY-IMAGE name.

              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 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 command 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

       -s     Silently proceed directly to the "crash>" prompt without
              displaying 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

       -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 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-

       -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 standalone 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=5level     (5-level page tables)
                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

       --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

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

              Do not access or display any kernel module related

              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
              infrastructure 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 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 dumpfiles 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 $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.

       --kaslr offset|auto
              If an x86_64 kernel was configured with CONFIG_RANDOMIZE_BASE,
              the offset value is equal to the difference 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 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.

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

COMMANDS         top

       Each crash command generally falls into one of the following

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

       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
       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

       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

       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

       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

       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 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.

       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 execution.

       runq   displays the tasks on the run queue.

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

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

       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

       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.

FILES         top

              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.

ENVIRONMENT         top

       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.

NOTES         top

       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.

AUTHOR         top

       Dave Anderson <> wrote crash.

       Jay Fenlason <> and Dave Anderson
       <> wrote this man page.

SEE ALSO         top

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

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

COLOPHON         top

       This page is part of the crash (Linux crash dump analyzer) project.
       Information about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, send it to  This page was
       obtained from the project's upstream Git repository
       ⟨⟩ on 2020-08-13.  (At
       that time, the date of the most recent commit that was found in the
       repository was 2020-08-12.)  If you discover any rendering problems
       in this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to