Readily available help information is built into the crash utility. During a session,
entering the
help
command with no argument shows the following menu:
Each command has its own man-like help page, which can be
viewed by clicking on the command name above.
Each help page details the syntax of the command and its available options,
a description of the command in general, a description of each option,
and a set of examples.
During a crash
session, a command's help page can be displayed by entering
help
followed by the command name.
So, for example, to get help on how to use the
set
command:
crash> help set
NAME
set - set a process context or internal crash variable
SYNOPSIS
set [pid | taskp | [-c cpu] | -p] | [crash_variable [setting]] | -v
DESCRIPTION
This command either sets a new context, or gets the current context for
display. The context can be set by the use of:
pid a process PID.
taskp a hexadecimal task_struct pointer.
-c cpu sets the context to the active task on a cpu (dumpfiles only).
-p sets the context to the panic task, or back to the crash task on
a live system.
-v display the current state of internal crash variables.
If no argument is entered, the current context is displayed. The context
consists of the PID, the task pointer, the CPU, and task state.
This command may also be used to set internal crash variables. If no value
argument is entered, the current value of the crash variable is shown. These
are the crash variables, acceptable arguments, and purpose:
scroll on | off controls output scrolling.
radix 10 | 16 sets output radix to 10 or 16.
refresh on | off controls internal task list refresh.
print_max number set maximum number of array elements to print.
console device-name sets debug console device.
debug number sets crash debug level.
core on | off if on, drops core when the next error message
is displayed.
hash on | off controls internal list verification.
silent on | off turns off initialization messages; turns off crash
prompt during input file execution. (scrolling is
turned off if silent is on)
edit vi | emacs set line editing mode (from .crashrc file only).
namelist filename name of kernel (from .crashrc file only).
dumpfile filename name of core dumpfile (from .crashrc file only).
Internal variables may be set in four manners:
1. entering the set command in $HOME/.crashrc.
2. entering the set command in .crashrc in the current directory.
3. executing an input file containing the set command.
4. during runtime with this command.
During initialization, $HOME/.crashrc is read first, followed by the
.crashrc file in the current directory. Set commands in the .crashrc file
in the current directory override those in $HOME/.crashrc. Set commands
entered with this command or by runtime input file override those
defined in either .crashrc file. Multiple set command arguments or argument
pairs may be entered in one command line.
EXAMPLES
Set the current context to task c2fe8000:
crash> set c2fe8000
PID: 15917
COMMAND: "bash"
TASK: c2fe8000
CPU: 0
STATE: TASK_INTERRUPTIBLE
Set the context back to the panicking task:
crash> set -p
PID: 698
COMMAND: "gen12"
TASK: f9d78000
CPU: 2
STATE: TASK_RUNNING (PANIC)
Turn off output scrolling:
crash> set scroll off
scroll: off
Show the current state of crash internal variables:
crash> set -v
scroll: on
radix: 10 (decimal)
refresh: on
print_max: 256
console: /dev/pts/2
debug: 0
core: off
hash: on
silent: off
edit: vi
namelist: vmlinux
dumpfile: vmcore
Show the current context:
crash> set
PID: 1525
COMMAND: "bash"
TASK: c1ede000
CPU: 0
STATE: TASK_INTERRUPTIBLE
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If for some reason a crash session cannot be invoked, but
help information for a particular crash command is desired, the same
help page can be displayed from a shell command line using the
-h option to crash:
# crash -h ascii
NAME
ascii - translate a hexadecimal string to ASCII
SYNOPSIS
ascii value ...
DESCRIPTION
Translates 32-bit or 64-bit hexadecimal values to ASCII. If no argument
is entered, an ASCII chart is displayed.
EXAMPLES
Translate the hexadecimal value of 0x62696c2f7273752f to ASCII:
crash> ascii 62696c2f7273752f
62696c2f7273752f: /usr/lib
Display an ASCII chart:
crash> ascii
0 1 2 3 4 5 6 7
+-------------------------------
0 | NUL DLE SP 0 @ P ' p
1 | SOH DC1 ! 1 A Q a q
2 | STX DC2 " 2 B R b r
3 | ETX DC3 # 3 C S c s
4 | EOT DC4 $ 4 D T d t
5 | ENQ NAK % 5 E U e u
6 | ACK SYN & 6 F V f v
7 | BEL ETB ` 7 G W g w
8 | BS CAN ( 8 H X h x
9 | HT EM ) 9 I Y i y
A | LF SUB * : J Z j z
B | VT ESC + ; K [ k {
C | FF FS , < L \ l |
D | CR GS _ = M ] m }
E | SO RS . > N ^ n ~
F | SI US / ? O - o DEL
#
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Lastly, help concerning command input and output can be displayed
by entering
help input
or
help output
during runtime,
or crash -h input or crash -h output from a shell
command line.
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