<s>
NILFS	B-Application
or	O
NILFS2	B-Application
(	O
New	O
Implementation	O
of	O
a	O
Log-structured	B-Application
File	I-Application
System	I-Application
)	O
is	O
a	O
log-structured	B-Application
file	I-Application
system	I-Application
implementation	O
for	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
.	O
</s>
<s>
NILFS	B-Application
was	O
released	O
under	O
the	O
terms	O
of	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GPL	B-License
)	O
.	O
</s>
<s>
"	O
NILFS	B-Application
is	O
a	O
log-structured	B-Application
file	I-Application
system	I-Application
,	O
in	O
that	O
the	O
storage	O
medium	O
is	O
treated	O
like	O
a	O
circular	O
buffer	O
and	O
new	O
blocks	O
are	O
always	O
written	O
to	O
the	O
end	O
.	O
</s>
<s>
[…]Log-structured	O
file	O
systems	O
are	O
often	O
used	O
for	O
flash	O
media	O
since	O
they	O
will	O
naturally	O
perform	O
wear-leveling;[…]NILFS	O
emphasizes	O
snapshots	B-Application
.	O
</s>
<s>
The	O
log-structured	O
approach	O
is	O
a	O
specific	O
form	O
of	O
copy-on-write	O
behavior	O
,	O
so	O
it	O
naturally	O
lends	O
itself	O
to	O
the	O
creation	O
of	O
file	B-Application
system	I-Application
snapshots	B-Application
.	O
</s>
<s>
The	O
NILFS	B-Application
developers	O
talk	O
about	O
the	O
creation	O
of	O
"	O
continuous	O
snapshots	B-Application
"	O
which	O
can	O
be	O
used	O
to	O
recover	O
from	O
user-initiated	O
file	B-Application
system	I-Application
problems[…].	O
 "	O
</s>
<s>
Using	O
a	O
copy-on-write	O
technique	O
known	O
as	O
"	O
nothing	O
in	O
life	O
is	O
free	O
"	O
,	O
NILFS	B-Application
records	O
all	O
data	O
in	O
a	O
continuous	O
log-like	O
format	O
that	O
is	O
only	O
appended	O
to	O
,	O
never	O
overwritten	O
,	O
an	O
approach	O
that	O
is	O
designed	O
to	O
reduce	O
seek	O
times	O
,	O
as	O
well	O
as	O
minimize	O
the	O
kind	O
of	O
data	B-General_Concept
loss	I-General_Concept
that	O
occurs	O
after	O
a	O
crash	B-General_Concept
with	O
conventional	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
data	B-General_Concept
loss	I-General_Concept
occurs	O
on	O
ext3	B-Application
file	B-Application
systems	I-Application
when	O
the	O
system	B-General_Concept
crashes	I-General_Concept
during	O
a	O
write	O
operation	O
.	O
</s>
<s>
When	O
the	O
system	B-Operating_System
reboots	I-Operating_System
,	O
the	O
journal	B-General_Concept
notes	O
that	O
the	O
write	O
did	O
not	O
complete	O
,	O
and	O
any	O
partial	O
data	O
writes	O
are	O
lost	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
,	O
like	O
UFS-derived	O
file	B-Application
systems	I-Application
used	O
by	O
the	O
Solaris	B-Application
operating	I-Application
system	I-Application
and	O
BSDs	B-Operating_System
,	O
provide	O
a	O
snapshot	B-Application
feature	O
that	O
prevents	O
such	O
data	B-General_Concept
loss	I-General_Concept
,	O
but	O
the	O
snapshot	B-Application
configuration	O
can	O
be	O
lengthy	O
on	O
large	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
NILFS	B-Application
,	O
in	O
contrast	O
,	O
can	O
"	O
continuously	O
and	O
automatically	O
 [ save ] 	O
instantaneous	O
states	O
of	O
the	O
file	B-Application
system	I-Application
without	O
interrupting	O
service	O
"	O
,	O
according	O
to	O
NTT	O
Labs	O
.	O
</s>
<s>
The	O
"	O
instantaneous	O
states	O
"	O
that	O
NILFS	B-Application
continuously	O
saves	O
can	O
actually	O
be	O
mounted	O
,	O
read-only	O
,	O
at	O
the	O
same	O
time	O
that	O
the	O
actual	O
file	B-Application
system	I-Application
is	O
mounted	O
read-write	O
—	O
a	O
capability	O
useful	O
for	O
data	O
recovery	O
after	O
hardware	O
failures	O
and	O
other	O
system	B-General_Concept
crashes	I-General_Concept
.	O
</s>
<s>
The	O
"	O
lscp	O
"	O
(	O
list	O
checkpoint	O
)	O
command	O
of	O
an	O
interactive	O
NILFS	B-Application
"	O
inspect	O
"	O
utility	O
is	O
first	O
used	O
to	O
find	O
the	O
checkpoint	O
's	O
address	O
,	O
in	O
this	O
case	O
"	O
2048	O
"	O
:	O
</s>
<s>
NILFS	B-Application
provides	O
continuous	O
snapshotting	B-Application
.	O
</s>
<s>
In	O
addition	O
to	O
versioning	O
capability	O
of	O
the	O
entire	O
file	B-Application
system	I-Application
,	O
users	O
can	O
even	O
restore	O
files	O
mistakenly	O
overwritten	O
or	O
deleted	O
at	O
any	O
recent	O
time	O
.	O
</s>
<s>
Since	O
NILFS	B-Application
can	O
keep	O
consistency	O
like	O
conventional	O
LFS	O
,	O
it	O
achieves	O
quick	O
recovery	O
after	O
system	B-General_Concept
crashes	I-General_Concept
.	O
</s>
<s>
Continuous	O
snapshotting	B-Application
is	O
not	O
provided	O
by	O
most	O
file	B-Application
systems	I-Application
,	O
including	O
those	O
supporting	O
point-in-time	O
snapshotting	B-Application
(	O
e.g.	O
</s>
<s>
NILFS	B-Application
creates	O
a	O
number	O
of	O
checkpoints	O
every	O
few	O
seconds	O
or	O
per	O
synchronous	O
write	O
basis	O
(	O
unless	O
there	O
is	O
no	O
change	O
)	O
.	O
</s>
<s>
Users	O
can	O
select	O
significant	O
versions	O
among	O
continuously	O
created	O
checkpoints	O
,	O
and	O
can	O
change	O
them	O
into	O
snapshots	B-Application
which	O
will	O
be	O
preserved	O
until	O
they	O
are	O
changed	O
back	O
to	O
checkpoints	O
.	O
</s>
<s>
There	O
is	O
no	O
limit	O
on	O
the	O
number	O
of	O
snapshots	B-Application
until	O
the	O
volume	O
gets	O
full	O
.	O
</s>
<s>
Each	O
snapshot	B-Application
is	O
mountable	O
as	O
a	O
read-only	O
file	B-Application
system	I-Application
.	O
</s>
<s>
It	O
is	O
mountable	O
concurrently	O
with	O
a	O
writable	O
mount	O
and	O
other	O
snapshots	B-Application
,	O
and	O
this	O
feature	O
is	O
convenient	O
to	O
make	O
consistent	O
backups	O
during	O
use	O
.	O
</s>
<s>
Possible	O
uses	O
of	O
NILFS	B-Application
include	O
versioning	O
,	O
tamper	O
detection	O
,	O
SOX	O
compliance	O
logging	O
,	O
data	B-General_Concept
loss	I-General_Concept
recovery	O
.	O
</s>
<s>
The	O
current	O
major	O
version	O
of	O
NILFS	B-Application
is	O
version	O
2	O
,	O
which	O
is	O
referred	O
to	O
as	O
NILFS2	B-Application
.	O
</s>
<s>
NILFS2	B-Application
implements	O
online	O
garbage	B-General_Concept
collection	I-General_Concept
to	O
reclaim	O
disk	O
space	O
with	O
keeping	O
multiple	O
snapshots	B-Application
.	O
</s>
<s>
Other	O
NILFS	B-Application
features	O
include	O
:	O
</s>
<s>
B-tree	B-Architecture
based	O
file	O
and	O
inode	O
management	O
.	O
</s>
<s>
Immediate	O
recovery	O
after	O
system	B-General_Concept
crash	I-General_Concept
.	O
</s>
<s>
64-bit	O
on-disk	O
timestamps	O
which	O
are	O
free	O
of	O
the	O
year	B-Application
2038	I-Application
problem	I-Application
.	I-Application
</s>
<s>
As	O
of	O
2023	O
,	O
NILFS	B-Application
lacks	O
in	O
dedicated	O
consistency	O
checking	O
utility	O
(	O
fsck	O
)	O
,	O
thus	O
it	O
can´t	O
recover	O
from	O
severe	O
errors	O
that	O
cause	O
it	O
to	O
fail	O
to	O
find	O
a	O
valid	O
checkpoint	O
.	O
</s>
<s>
Block	B-General_Concept
sizes	I-General_Concept
smaller	O
than	O
page	B-General_Concept
size	I-General_Concept
(	O
e.g.	O
</s>
<s>
NILFS	B-Application
is	O
available	O
in	O
various	O
GNU/Linux	B-Application
distributions	I-Application
like	O
Arch	O
Linux	B-Operating_System
,	O
Debian	O
(	O
since	O
version	O
5.0	O
)	O
,	O
Fedora	O
,	O
Gentoo	B-Application
,	O
Linux	B-Application
Mint	I-Application
,	O
NixOS	O
,	O
Ubuntu	B-Operating_System
(	O
since	O
version	O
9.10	O
)	O
,	O
etc	O
.	O
</s>
<s>
To	O
use	O
it	O
,	O
users	O
typically	O
need	O
to	O
install	O
the	O
nilfs-utils	O
or	O
nilfs-tools	O
package	O
.	O
</s>
<s>
A	O
boot-cd	O
with	O
NILFS	B-Application
is	O
also	O
available	O
on	O
.	O
</s>
<s>
It	O
is	O
also	O
supported	O
by	O
partition-editing	O
application	O
like	O
GParted	B-Application
.	O
</s>
<s>
A	O
separate	O
,	O
BSD	B-Operating_System
licensed	O
implementation	O
,	O
currently	O
with	O
read-only	O
support	O
,	O
is	O
included	O
in	O
NetBSD	B-Device
.	O
</s>
<s>
In	O
the	O
January	O
2015	O
presentation	O
SD	B-Device
cards	I-Device
and	O
file	B-Application
systems	I-Application
for	O
embedded	B-Architecture
systems	I-Architecture
at	O
Linux.conf.au,	O
it	O
was	O
stated	O
:	O
</s>
<s>
The	O
NILFS2	B-Application
file	B-Application
system	I-Application
utilities	O
are	O
made	O
available	O
under	O
the	O
GNU	B-License
Public	I-License
License	I-License
version	O
2	O
,	O
with	O
the	O
exception	O
of	O
the	O
lib/nilfs	O
libraries	O
and	O
their	O
header	O
files	O
,	O
which	O
are	O
made	O
available	O
under	O
the	O
GNU	O
Lesser	O
General	B-License
Public	I-License
License	I-License
Version	O
2.1	O
.	O
</s>
<s>
The	O
Japanese	O
primary	O
authors	O
and	O
major	O
contributors	O
to	O
the	O
nilfs-utils	O
who	O
worked	O
or	O
are	O
working	O
at	O
labs	O
of	O
NTT	O
Corporation	O
are	O
:	O
</s>
