crash(8) -- Linux man page



crash - Analyze Linux crash data or a live system  


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


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 command, 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 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.  


-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.
Crash displays the versions of the original gdb and crash libraries that make up the crash executable.
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.
Crash uses "/boot/" as the mapfile.
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.
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 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.
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.


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.
creates a single-word alias for a command.
displays an ascii chart or translates a numeric value into its ascii components.
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.
translates a byte value (physical offset) to it's page number.
displays data concerning the character and block device assignments, I/O port usage, I/O memory usage, and PCI device data.
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.
evalues an expression or numeric type and displays the result in hexidecimal, decimal, octal and binary.
causes crash to exit.
dynamically loads or unloads crash extension shared object libraries.
displays information about open files in a context.
repeats a specified command for the specified (or all) tasks in the system.
displays the tasks using the specifed file or socket.
passes its argument to the underlying gdb program. It is useful for executing GDB commands that have the same name as crash commands.
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.
displays data concerning interrupt request numbers and bottom-half interrupt handling.
displays information about the use of kernel memory.
displays the contents of a linked list.
displays the kernel log_buf contents in chronological order.
displays data specific to the machine type.
displays information about the currently installed kernel modules, or adds or deletes symbolic or debugging information about specified kernel modules.
displays information about the currently-mounted filesystems.
display various network related data.
passes its argumnts to the gdb "print" command for evaluation and display.
displays process status for specified, or all, processes in the system.
translates the hexadecimal contents of a PTE into its physical page address and page bit settings.
translates a page frame number to its byte value.
translates a hexadecimal physical address into a kernel virtual address.
is an alias for the "exit" command.
displays the contents of memory, with the output formatted in several different manners.
repeats a command indefinitely, optionally delaying a given number of seconds between each command execution.
displays the tasks on the run queue.
searches a range of user or kernel memory space for given value.
either sets a new context, or gets the current context for display.
displays signal-handling data of one or more tasks.
displays either a structure definition or the contents of a kernel structure at a specified address.
displays information about each configured swap device.
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.
displays system-specific data.
displays the contents of a task_struct.
displays the timer queue entries, both old- and new-style, in chronological order.
is similar to the struct command, except that it works on kernel unions.
displays basic virtual memory information of a context.
translates a user or kernel virtual address to its physical address.
walks the wait queue list displaying the tasks which are blocked on the specified wait queue.
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.


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


netdump(8) gdb(1)