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 Red Hat
netdump,diskdump,kdump,
or
xendump
facilities. It is loosely based on the SVR4 UNIX crash
command, but has been significantly enhanced
by completely merging it with the
gdb
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.
The current set of commands consist 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.
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
-h opt
Crash
displays a help message. If the optional
opt
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.
-v
Crash
displays the versions of the original gdb and crash libraries
that make up the
crash
executable.
-s
Crash
does not display any version, GPL, or crash initialization data during startup. It
proceeds directly to the "crash>" prompt.
-i file
Crash
reads and executes the crash command(s) contained in
file
before accepting any user input.
-d num
Crash
sets its internal debug level.
The higher the number, the more debugging data will be printed while
crash
runs.
-S
Crash
uses "/boot/System.map" as the
mapfile.
namelist
This is a pathname to an uncompressed kernel image
(a vmlinux file) that has been compiled with the "-g" option,
or that has an accessible, associated, debuginfo file.
If the
dumpfile
argument is entered, then this argument must also be used. If the
namelist
argument is not entered and no
dumpfile
argument is entered,
crash
will search in several typical directories
for a kernel namelist that matches the live system.
mapfile
If the live system kernel, or the kernel from which the
dumpfile
was derived, was not compiled with the -g switch, then the additional
mapfile
argument is required. It may be either the associated System.map file, or
the non-debug kernel namelist. However, if the
mapfile
argument is used, then the
namelist
argument must be a kernel namelist of a similar kernel
version that was built with the -g switch.
dumpfile
This is a pathname to a kernel memory core dump
file. If the
dumpfile
argument is not entered, the session will be invoked on the live system
using /dev/mem, which usually requires root privileges.
COMMANDS
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 come 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 entering the command
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 it's 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
evalues 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 extension shared object
libraries.
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 underlying
gdb
program. 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.
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 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.
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. When writing to memory on
a live system, this command should obviously be used with great care.
FILES
.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.
ENVIRONMENT
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.
NOTES
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.
