<s>
In	O
computing	O
,	O
a	O
crash	B-General_Concept
,	O
or	O
system	B-General_Concept
crash	I-General_Concept
,	O
occurs	O
when	O
a	O
computer	B-Application
program	I-Application
such	O
as	O
a	O
software	B-Application
application	I-Application
or	O
an	O
operating	B-General_Concept
system	I-General_Concept
stops	O
functioning	O
properly	O
and	O
exits	B-Operating_System
.	O
</s>
<s>
On	O
some	O
operating	B-General_Concept
systems	I-General_Concept
or	O
individual	O
applications	O
,	O
a	O
crash	B-Operating_System
reporting	I-Operating_System
service	I-Operating_System
will	O
report	O
the	O
crash	B-General_Concept
and	O
any	O
details	O
relating	O
to	O
it	O
(	O
or	O
give	O
the	O
user	O
the	O
option	O
to	O
do	O
so	O
)	O
,	O
usually	O
to	O
the	O
developer(s )	O
of	O
the	O
application	B-Application
.	O
</s>
<s>
If	O
the	O
program	B-Application
is	O
a	O
critical	O
part	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
the	O
entire	O
system	O
may	O
crash	B-General_Concept
or	O
hang	O
,	O
often	O
resulting	O
in	O
a	O
kernel	B-Operating_System
panic	I-Operating_System
or	O
fatal	B-Error_Name
system	I-Error_Name
error	I-Error_Name
.	O
</s>
<s>
Most	O
crashes	B-General_Concept
are	O
the	O
result	O
of	O
a	O
software	B-Error_Name
bug	I-Error_Name
.	O
</s>
<s>
Typical	O
causes	O
include	O
accessing	B-Error_Name
invalid	I-Error_Name
memory	I-Error_Name
addresses	I-Error_Name
,	O
incorrect	O
address	B-General_Concept
values	O
in	O
the	O
program	B-General_Concept
counter	I-General_Concept
,	O
buffer	B-General_Concept
overflow	I-General_Concept
,	O
overwriting	O
a	O
portion	O
of	O
the	O
affected	O
program	B-Application
code	O
due	O
to	O
an	O
earlier	O
bug	B-Error_Name
,	O
executing	O
invalid	O
machine	B-Language
instructions	I-Language
(	O
an	O
illegal	B-Language
opcode	I-Language
)	O
,	O
or	O
triggering	O
an	O
unhandled	B-General_Concept
exception	I-General_Concept
.	O
</s>
<s>
The	O
original	O
software	B-Error_Name
bug	I-Error_Name
that	O
started	O
this	O
chain	O
of	O
events	O
is	O
typically	O
considered	O
to	O
be	O
the	O
cause	O
of	O
the	O
crash	B-General_Concept
,	O
which	O
is	O
discovered	O
through	O
the	O
process	O
of	O
debugging	O
.	O
</s>
<s>
The	O
original	O
bug	B-Error_Name
can	O
be	O
far	O
removed	O
from	O
the	O
code	O
that	O
actually	O
triggered	O
the	O
crash	B-General_Concept
.	O
</s>
<s>
In	O
early	O
personal	O
computers	O
,	O
attempting	O
to	O
write	O
data	O
to	O
hardware	B-Architecture
addresses	O
outside	O
the	O
system	O
's	O
main	O
memory	O
could	O
cause	O
hardware	B-Architecture
damage	O
.	O
</s>
<s>
Some	O
crashes	B-General_Concept
are	O
exploitable	O
and	O
let	O
a	O
malicious	O
program	B-Application
or	O
hacker	B-Application
execute	O
arbitrary	O
code	O
allowing	O
the	O
replication	O
of	O
viruses	O
or	O
the	O
acquisition	O
of	O
data	O
which	O
would	O
normally	O
be	O
inaccessible	O
.	O
</s>
<s>
An	O
application	B-Application
typically	O
crashes	B-General_Concept
when	O
it	O
performs	O
an	O
operation	O
that	O
is	O
not	O
allowed	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
then	O
triggers	O
an	O
exception	B-General_Concept
or	O
signal	B-Operating_System
in	O
the	O
application	B-Application
.	O
</s>
<s>
Unix	O
applications	O
traditionally	O
responded	O
to	O
the	O
signal	B-Operating_System
by	O
dumping	B-Error_Name
core	I-Error_Name
.	O
</s>
<s>
Most	O
Windows	O
and	O
Unix	O
GUI	B-Application
applications	O
respond	O
by	O
displaying	O
a	O
dialogue	O
box	O
(	O
such	O
as	O
the	O
one	O
shown	O
to	O
the	O
right	O
)	O
with	O
the	O
option	O
to	O
attach	O
a	O
debugger	B-Application
if	O
one	O
is	O
installed	O
.	O
</s>
<s>
Some	O
applications	O
attempt	O
to	O
recover	O
from	O
the	O
error	O
and	O
continue	O
running	O
instead	O
of	O
exiting	B-Operating_System
.	O
</s>
<s>
An	O
application	B-Application
can	O
also	O
contain	O
code	O
to	O
crash	B-General_Concept
after	O
detecting	O
a	O
severe	O
error	O
.	O
</s>
<s>
Typical	O
errors	O
that	O
result	O
in	O
application	B-General_Concept
crashes	I-General_Concept
include	O
:	O
</s>
<s>
attempting	O
to	O
execute	O
machine	B-Language
instructions	I-Language
with	O
bad	O
arguments	O
(	O
depending	O
on	O
CPU	O
architecture	O
)	O
:	O
divide	B-Algorithm
by	I-Algorithm
zero	I-Algorithm
,	O
operations	O
on	O
denormal	B-Algorithm
number	I-Algorithm
or	O
NaN	O
(	O
not	O
a	O
number	O
)	O
values	O
,	O
memory	O
access	O
to	O
unaligned	B-General_Concept
addresses	I-General_Concept
,	O
etc	O
.	O
</s>
<s>
A	O
"	O
crash	B-General_Concept
to	O
desktop	B-Application
"	O
is	O
said	O
to	O
occur	O
when	O
a	O
program	B-Application
(	O
commonly	O
a	O
video	O
game	O
)	O
unexpectedly	O
quits	O
,	O
abruptly	O
taking	O
the	O
user	O
back	O
to	O
the	O
desktop	B-Application
.	O
</s>
<s>
Usually	O
,	O
the	O
term	O
is	O
applied	O
only	O
to	O
crashes	B-General_Concept
where	O
no	O
error	O
is	O
displayed	O
,	O
hence	O
all	O
the	O
user	O
sees	O
as	O
a	O
result	O
of	O
the	O
crash	B-General_Concept
is	O
the	O
desktop	B-Application
.	O
</s>
<s>
Many	O
times	O
there	O
is	O
no	O
apparent	O
action	O
that	O
causes	O
a	O
crash	B-General_Concept
to	O
desktop	B-Application
.	O
</s>
<s>
During	O
normal	O
function	O
,	O
the	O
program	B-Application
may	O
freeze	B-General_Concept
for	O
a	O
shorter	O
period	O
of	O
time	O
,	O
and	O
then	O
close	O
by	O
itself	O
.	O
</s>
<s>
Also	O
during	O
normal	O
function	O
,	O
the	O
program	B-Application
may	O
become	O
a	O
black	B-Error_Name
screen	I-Error_Name
and	O
repeatedly	O
play	O
the	O
last	O
few	O
seconds	O
of	O
sound	O
(	O
depending	O
on	O
the	O
size	O
of	O
the	O
audio	O
buffer	B-General_Concept
)	O
that	O
was	O
being	O
played	O
before	O
it	O
crashes	B-General_Concept
to	O
desktop	B-Application
.	O
</s>
<s>
Crash	B-General_Concept
to	O
desktop	B-Application
bugs	B-Error_Name
are	O
considered	O
particularly	O
problematic	O
for	O
users	O
.	O
</s>
<s>
Since	O
they	O
frequently	O
display	O
no	O
error	O
message	O
,	O
it	O
can	O
be	O
very	O
difficult	O
to	O
track	O
down	O
the	O
source	O
of	O
the	O
problem	O
,	O
especially	O
if	O
the	O
times	O
they	O
occur	O
and	O
the	O
actions	O
taking	O
place	O
right	O
before	O
the	O
crash	B-General_Concept
do	O
not	O
appear	O
to	O
have	O
any	O
pattern	O
or	O
common	O
ground	O
.	O
</s>
<s>
Windows	B-Application
Vista	I-Application
has	O
a	O
feature	O
that	O
can	O
help	O
track	O
down	O
the	O
cause	O
of	O
a	O
CTD	O
problem	O
when	O
it	O
occurs	O
on	O
any	O
program	B-Application
.	O
</s>
<s>
Windows	B-Application
XP	I-Application
included	O
a	O
similar	O
feature	O
as	O
well	O
.	O
</s>
<s>
Some	O
computer	B-Application
programs	I-Application
,	O
such	O
as	O
StepMania	B-Language
and	O
BBC	O
's	O
Bamzooki	O
,	O
also	O
crash	B-General_Concept
to	O
desktop	B-Application
if	O
in	O
full-screen	O
,	O
but	O
display	O
the	O
error	O
in	O
a	O
separate	O
window	O
when	O
the	O
user	O
has	O
returned	O
to	O
the	O
desktop	B-Application
.	O
</s>
<s>
The	O
software	O
running	O
the	O
web	B-Application
server	I-Application
behind	O
a	O
website	O
may	O
crash	B-General_Concept
,	O
rendering	O
it	O
inaccessible	O
entirely	O
or	O
providing	O
only	O
an	O
error	O
message	O
instead	O
of	O
normal	O
content	O
.	O
</s>
<s>
For	O
example	O
:	O
if	O
a	O
site	O
is	O
using	O
an	O
SQL	O
database	O
(	O
such	O
as	O
MySQL	B-Application
)	O
for	O
a	O
script	O
(	O
such	O
as	O
PHP	B-Application
)	O
and	O
that	O
SQL	O
database	O
server	O
crashes	B-General_Concept
,	O
then	O
PHP	B-Application
will	O
display	O
a	O
connection	O
error	O
.	O
</s>
<s>
An	O
operating	B-General_Concept
system	I-General_Concept
crash	I-General_Concept
commonly	O
occurs	O
when	O
a	O
hardware	B-General_Concept
exception	I-General_Concept
occurs	O
that	O
cannot	O
be	O
handled	B-General_Concept
.	O
</s>
<s>
Operating	B-General_Concept
system	I-General_Concept
crashes	I-General_Concept
can	O
also	O
occur	O
when	O
internal	O
sanity-checking	B-Error_Name
logic	O
within	O
the	O
operating	B-General_Concept
system	I-General_Concept
detects	O
that	O
the	O
operating	B-General_Concept
system	I-General_Concept
has	O
lost	O
its	O
internal	O
self-consistency	O
.	O
</s>
<s>
Modern	O
multi-tasking	O
operating	B-General_Concept
systems	I-General_Concept
,	O
such	O
as	O
Linux	B-Application
,	O
and	O
macOS	B-Application
,	O
usually	O
remain	O
unharmed	O
when	O
an	O
application	B-Application
program	I-Application
crashes	B-General_Concept
.	O
</s>
<s>
Some	O
operating	B-General_Concept
systems	I-General_Concept
,	O
e.g.	O
,	O
z/OS	B-Application
,	O
have	O
facilities	O
for	O
Reliability	B-General_Concept
,	I-General_Concept
availability	I-General_Concept
and	I-General_Concept
serviceability	I-General_Concept
(	O
RAS	O
)	O
and	O
the	O
OS	O
can	O
recover	O
from	O
the	O
crash	B-General_Concept
of	O
a	O
critical	O
component	O
,	O
whether	O
due	O
to	O
hardware	B-Architecture
failure	O
,	O
e.g.	O
,	O
uncorrectable	O
ECC	O
error	O
,	O
or	O
to	O
software	B-Error_Name
failure	I-Error_Name
,	O
e.g.	O
,	O
a	O
reference	O
to	O
an	O
unassigned	O
page	O
.	O
</s>
<s>
Depending	O
on	O
the	O
application	B-Application
,	O
the	O
crash	B-General_Concept
may	O
contain	O
the	O
user	O
's	O
sensitive	O
and	O
private	O
information	O
.	O
</s>
<s>
Moreover	O
,	O
many	O
software	B-Error_Name
bugs	I-Error_Name
which	O
cause	O
crashes	B-General_Concept
are	O
also	O
exploitable	O
for	O
arbitrary	O
code	O
execution	O
and	O
other	O
types	O
of	O
privilege	O
escalation	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
stack	B-General_Concept
buffer	I-General_Concept
overflow	I-General_Concept
can	O
overwrite	O
the	O
return	O
address	B-General_Concept
of	O
a	O
subroutine	O
with	O
an	O
invalid	O
value	O
,	O
which	O
will	O
cause	O
,	O
e.g.	O
,	O
a	O
segmentation	B-Error_Name
fault	I-Error_Name
,	O
when	O
the	O
subroutine	O
returns	O
.	O
</s>
<s>
However	O
,	O
if	O
an	O
exploit	O
overwrites	O
the	O
return	O
address	B-General_Concept
with	O
a	O
valid	O
value	O
,	O
the	O
code	O
in	O
that	O
address	B-General_Concept
will	O
be	O
executed	O
.	O
</s>
<s>
When	O
crashes	B-General_Concept
are	O
collected	O
in	O
the	O
field	O
using	O
a	O
crash	B-Operating_System
reporter	I-Operating_System
,	O
the	O
next	O
step	O
for	O
developers	B-Application
is	O
to	O
be	O
able	O
to	O
reproduce	O
them	O
locally	O
.	O
</s>
