crash - phpMan

CRASH(8) CRASH(8)

NAME
crash - Analyze Linux crash data or a live system

SYNAPSIS
crash [ -h [ opt ] ] [ -v ] [ -s ] [ -i file ] [ -d num ] [ -S ] [ mapfile ] [
namelist ] [ dumpfile ]

DESCRIPTION
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 facility. It is loosely based on the SVR4 UNIX crash com-
mand, but has been signficantly 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 capabil-
ities 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 ker-
nel structure and variable displays, virtual memory data, dumps of linked-lists,
etc., along with several commands that delve deeper into specific kernel subsys-
tems. 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 main-
taining backwards compatibility with earlier releases.

OPTIONS
-h opt Crash displays a help message. If the optional opt 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.

-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 debug-
ging 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 argu-
ment 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" com-
mands, 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, oth-
ers 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 dis-
plays 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 compo-
nents.

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 fuction up to a
specified memory location.

eval evalues an expression or numeric type and displays the result in hexideci-
mal, 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 specifed file or socket.

gdb passes its argument to the underlying gdb program. It is useful for execut-
ing 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 out-
put 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 argumnts 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 dif-
ferent manners.

repeat repeats a command indefinitely, optionally delaying a given number of sec-
onds 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 sym-
bols. wr modifies the contents of memory. When writing to memory on a live
system, this command should obviously be used with great care.

AUTHOR
Dave Anderson <anderson AT redhat.com> wrote Crash

Jay Fenlason <fenlason AT redhat.com> wrote this man page.