<s>
Cowloop	B-Application
(	O
copy-on-write	B-Language
loop	O
driver	O
)	O
was	O
a	O
Linux	B-Operating_System
kernel	I-Operating_System
driver	O
that	O
allows	O
read-only	O
filesystems	B-Application
to	O
be	O
made	O
writable	O
using	O
the	O
kernel	B-Operating_System
module	O
cowloop.ko	O
.	O
</s>
<s>
Cowloop	B-Application
worked	O
by	O
writing	O
modified	O
blocks	O
to	O
a	O
separate	O
file	O
known	O
as	O
a	O
cowfile	O
,	O
which	O
is	O
created	O
by	O
using	O
the	O
cowdev	O
command	O
to	O
associate	O
a	O
block	O
device	O
,	O
such	O
as	O
a	O
CD	O
,	O
to	O
a	O
writable	O
file	O
.	O
</s>
<s>
Cowloop	B-Application
is	O
now	O
largely	O
deprecated	O
in	O
favor	O
of	O
the	O
device-mapper	B-Application
snapshot	O
target	O
which	O
provides	O
the	O
same	O
functionality	O
and	O
is	O
also	O
integrated	O
with	O
LVM2	B-Application
(	O
Linux	B-Operating_System
Logical	B-Application
Volume	I-Application
Manager	I-Application
version	O
2	O
)	O
.	O
</s>
<s>
Cowloop	B-Application
provided	O
a	O
somewhat	O
similar	O
functionality	O
to	O
unionfs	B-Application
and	O
the	O
newer	O
aufs	B-Application
,	O
but	O
operates	O
on	O
a	O
block	O
level	O
instead	O
of	O
operating	O
on	O
a	O
file	B-Application
system	I-Application
level	O
.	O
</s>
<s>
It	O
is	O
free	B-Application
software	I-Application
released	O
under	O
the	O
terms	O
of	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
v2	O
or	O
later	O
.	O
</s>
