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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | COMMANDS | FILES | ENVIRONMENT | NOTES | AUTHOR | SEE ALSO | COLOPHON |
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CRASH(8) System Manager's Manual 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 kernel crash has
occurred and a core dump has been created by the netdump,
diskdump, LKCD, kdump, xendump kvmdump or VMware 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> 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 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.
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 formats.
MEMORY-IMAGE[@ADDRESS]
A kernel core dump file created by the netdump, diskdump,
LKCD kdump, xendump kvmdump or VMware 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.
As VMware facility, the crash utility is able to process
VMware VM memory dump generated by VM suspend or guest
core dump. In that case, .vmss or .guest file should be
used as a MEMORY-IMAGE and .vmem file must be located in
the same folder.
mapfile
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
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 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 exits.
-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 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.
-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-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 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:
X86_64:
phys_base=<physical-address>
irq_eframe_link=<value>
irq_stack_gap=<value>
max_physmem_bits=<value>
kernel_image_size=<value>
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)
page_offset=<PAGE_OFFSET-value>
PPC64:
vm=orig
vm=2.6.14 (4-level page tables)
IA64:
phys_start=<physical-address>
init_stack_size=<size>
vm=4l (4-level page tables)
ARM:
phys_base=<physical-address>
ARM64:
phys_offset=<physical-address>
kimage_voffset=<kimage_voffset-value>
max_physmem_bits=<value>
vabits_actual=<value>
X86:
page_offset=<CONFIG_PAGE_OFFSET-value>
-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.
--active
Track only the active task on each cpu.
--buildinfo
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 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.
--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
infrastructure until it is required by a run-time command.
--readnow
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.
-v
--version
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.
--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 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.
--zero_excluded
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.
--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.
--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.
--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_strip
Do not strip cloned kernel text symbol names.
--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 of in the standard location.
--src directory
Search for the kernel source code in directory instead of
in the standard location that is compiled into the
debuginfo data.
--kaslr offset|auto
If an x86, x86_64, s390x or loongarch64 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.
--minimal
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.
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 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 union.
alias creates a single-word alias for a command.
ascii displays an ascii chart or translates a numeric value into
its ascii components.
bpf provides information on currently-loaded eBPF programs and
maps.
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 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
modules.
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 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 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.
sbitmapq
dumps the contents of the sbitmap_queue structure and the
used bits in the bitmap. Also, it shows the dump of a
structure array associated with the sbitmap_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.
dumpinfo
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.
.crashrc
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.
CRASHPAGER
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.
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.
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 <[email protected]> wrote crash.
Jay Fenlason <[email protected]> and Dave Anderson
<[email protected]> wrote this man page.
The help command within crash provides more complete and accurate
documentation than this man page.
https://github.com/crash-utility - the home page of the crash
utility.
netdump(8), gdb(1), makedumpfile(8)
This page is part of the crash (Linux crash dump analyzer)
project. Information about the project can be found at
⟨http://people.redhat.com/anderson/⟩. If you have a bug report
for this manual page, send it to [email protected]. This
page was obtained from the project's upstream Git repository
⟨https://github.com/crash-utility/crash.git⟩ on 2024-06-14. (At
that time, the date of the most recent commit that was found in
the repository was 2024-06-12.) 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
[email protected]
CRASH(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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