<s>
cksum	B-Device
is	O
a	O
command	B-Application
in	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
that	O
generates	O
a	O
checksum	B-Algorithm
value	O
for	O
a	O
file	O
or	O
stream	O
of	O
data	O
.	O
</s>
<s>
The	O
cksum	B-Device
command	B-Application
reads	O
each	O
file	O
given	O
in	O
its	O
arguments	O
,	O
or	O
standard	B-Operating_System
input	I-Operating_System
if	O
no	O
arguments	O
are	O
provided	O
,	O
and	O
outputs	O
the	O
file	O
's	O
32-bit	O
cyclic	O
redundancy	O
check	O
(	O
CRC	O
)	O
checksum	B-Algorithm
and	O
byte	B-Application
count	O
.	O
</s>
<s>
The	O
CRC	O
output	O
by	O
cksum	B-Device
is	O
different	O
from	O
the	O
CRC-32	O
used	O
in	O
zip	O
,	O
PNG	O
and	O
zlib	O
.	O
</s>
<s>
The	O
cksum	B-Device
command	B-Application
can	O
be	O
used	O
to	O
verify	O
that	O
files	O
transferred	O
by	O
unreliable	O
means	O
arrived	O
intact	O
.	O
</s>
<s>
However	O
,	O
the	O
CRC	O
checksum	B-Algorithm
calculated	O
by	O
the	O
cksum	B-Device
command	B-Application
is	O
not	O
cryptographically	B-Algorithm
secure	I-Algorithm
:	O
While	O
it	O
guards	O
against	O
accidental	O
corruption	O
(	O
it	O
is	O
unlikely	O
that	O
the	O
corrupted	O
data	O
will	O
have	O
the	O
same	O
checksum	B-Algorithm
as	O
the	O
intended	O
data	O
)	O
,	O
it	O
is	O
not	O
difficult	O
for	O
an	O
attacker	O
to	O
deliberately	O
corrupt	O
the	O
file	O
in	O
a	O
specific	O
way	O
that	O
its	O
checksum	B-Algorithm
is	O
unchanged	O
.	O
</s>
<s>
Unix-like	B-Operating_System
systems	I-Operating_System
typically	O
include	O
other	O
commands	O
for	O
cryptographically	B-Algorithm
secure	I-Algorithm
checksums	B-Algorithm
,	O
such	O
as	O
sha256sum	O
.	O
</s>
<s>
The	O
command	B-Application
is	O
available	O
as	O
a	O
separate	O
package	O
for	O
Microsoft	B-Application
Windows	I-Application
as	O
part	O
of	O
the	O
UnxUtils	B-Application
collection	O
of	O
native	B-Language
Win32	B-Library
ports	O
of	O
common	O
GNU	O
Unix-like	B-Operating_System
utilities	O
.	O
</s>
<s>
Latest	O
GNU	B-Application
Coreutils	I-Application
cksum	B-Device
provides	O
additional	O
checksum	B-Algorithm
algorithms	I-Algorithm
via	O
-a	O
option	O
,	O
as	O
an	O
extension	O
beyond	O
POSIX	O
.	O
</s>
<s>
The	O
standard	O
cksum	B-Device
command	B-Application
,	O
as	O
found	O
on	O
most	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
(	O
including	O
Linux	B-Application
,	O
*	B-Operating_System
BSD	I-Operating_System
,	O
macOS	B-Application
,	O
and	O
Solaris	B-Application
)	O
uses	O
a	O
CRC	O
algorithm	O
based	O
on	O
the	O
ethernet	B-Protocol
standard	I-Protocol
frame	I-Protocol
check	I-Protocol
and	O
is	O
therefore	O
interoperable	O
between	O
implementations	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
the	O
sum	O
command	B-Application
,	O
which	O
is	O
not	O
as	O
interoperable	O
and	O
not	O
compatible	O
with	O
the	O
CRC-32	O
calculation	O
.	O
</s>
<s>
On	O
Tru64	B-Operating_System
operating	B-General_Concept
systems	I-General_Concept
,	O
the	O
cksum	B-Device
command	B-Application
returns	O
a	O
different	O
CRC	O
value	O
,	O
unless	O
the	O
environment	O
variable	O
CMD_ENV	O
is	O
set	O
to	O
xpg4	O
.	O
</s>
<s>
cksum	B-Device
uses	O
the	O
generator	O
polynomial	O
0x04C11DB7	O
and	O
appends	O
to	O
the	O
message	O
its	O
length	O
in	O
little	O
endian	O
representation	O
.	O
</s>
<s>
That	O
length	O
has	O
null	O
bytes	B-Application
trimmed	O
on	O
the	O
right	O
end	O
.	O
</s>
<s>
where	O
4038471504	O
represents	O
the	O
checksum	B-Algorithm
value	O
and	O
75	O
represents	O
the	O
file	O
size	O
of	O
test.txt	O
.	O
</s>
