<s>
Extended	B-Application
file	I-Application
attributes	I-Application
are	O
file	B-Application
system	I-Application
features	O
that	O
enable	O
users	O
to	O
associate	O
computer	B-Operating_System
files	I-Operating_System
with	O
metadata	O
not	O
interpreted	O
by	O
the	O
filesystem	B-Application
,	O
whereas	O
regular	O
attributes	O
have	O
a	O
purpose	O
strictly	O
defined	O
by	O
the	O
filesystem	B-Application
(	O
such	O
as	O
permissions	O
or	O
records	O
of	O
creation	O
and	O
modification	O
times	O
)	O
.	O
</s>
<s>
Unlike	O
forks	B-Application
,	O
which	O
can	O
usually	O
be	O
as	O
large	O
as	O
the	O
maximum	O
file	O
size	O
,	O
extended	B-Application
attributes	I-Application
are	O
usually	O
limited	O
in	O
size	O
to	O
a	O
value	O
significantly	O
smaller	O
than	O
the	O
maximum	O
file	O
size	O
.	O
</s>
<s>
Typical	O
uses	O
include	O
storing	O
the	O
author	O
of	O
a	O
document	O
,	O
the	O
character	B-General_Concept
encoding	I-General_Concept
of	O
a	O
plain-text	O
document	O
,	O
or	O
a	O
checksum	O
,	O
cryptographic	B-Algorithm
hash	I-Algorithm
or	O
digital	O
certificate	O
,	O
and	O
discretionary	O
access	O
control	O
information	O
.	O
</s>
<s>
In	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
extended	B-Application
attributes	I-Application
are	O
usually	O
abbreviated	O
as	O
xattr	B-Application
.	O
</s>
<s>
In	O
AIX	B-Application
,	O
the	O
JFS2	B-Application
v2	O
filesystem	B-Application
supports	O
extended	B-Application
attributes	I-Application
,	O
which	O
are	O
accessible	O
using	O
the	O
command	O
.	O
</s>
<s>
The	O
,	O
,	O
,	O
,	O
and	O
APIs	O
support	O
fetching	O
,	O
setting	O
,	O
listing	O
,	O
getting	O
information	O
about	O
,	O
and	O
removing	O
extended	B-Application
attributes	I-Application
.	O
</s>
<s>
In	O
the	O
now-defunct	O
BeOS	B-Application
and	O
successors	O
like	O
Haiku	B-Language
,	O
extended	B-Application
file	I-Application
attributes	I-Application
are	O
widely	O
used	O
in	O
base	O
and	O
third-party	O
programs	O
.	O
</s>
<s>
The	O
Be	B-Language
File	I-Language
System	I-Language
allows	O
the	O
indexing	O
and	O
querying	O
of	O
attributes	O
,	O
essentially	O
giving	O
the	O
filesystem	B-Application
database-like	O
characteristics	O
.	O
</s>
<s>
The	O
uses	O
of	O
extended	B-Application
attributes	I-Application
in	O
Be-like	O
systems	O
are	O
varied	O
:	O
For	O
example	O
,	O
Tracker	B-Application
and	O
OpenTracker	B-Language
,	O
the	O
file-managers	O
of	O
BeOS	B-Application
and	O
Haiku	B-Language
respectively	O
,	O
both	O
store	O
the	O
locations	O
of	O
file	O
icons	O
in	O
attributes	O
,	O
Haiku	B-Language
's	O
"	O
Mail	O
"	O
service	O
stores	O
all	O
message	O
content	O
and	O
metadata	O
in	O
extended	B-Application
file	I-Application
attributes	I-Application
,	O
and	O
the	O
MIME	O
types	O
of	O
files	O
are	O
stored	O
in	O
their	O
attributes	O
.	O
</s>
<s>
Extended	B-Application
file	I-Application
attributes	I-Application
can	O
be	O
viewed	O
and	O
edited	O
in	O
Be-like	O
systems	O
 '	O
GUI	O
through	O
the	O
file-manager	O
,	O
often	O
Tracker	B-Application
or	O
derivatives	O
thereof	O
.	O
</s>
<s>
In	O
FreeBSD	B-Operating_System
5.0	O
and	O
later	O
,	O
the	O
UFS1	B-Operating_System
,	O
UFS2	O
,	O
and	O
ZFS	B-Application
filesystems	B-Application
support	O
extended	B-Application
attributes	I-Application
,	O
using	O
the	O
family	O
of	O
system	O
calls	O
.	O
</s>
<s>
Any	O
regular	O
file	O
may	O
have	O
a	O
list	O
of	O
extended	B-Application
attributes	I-Application
.	O
</s>
<s>
The	O
name	O
must	O
be	O
a	O
null-terminated	B-Data_Structure
string	I-Data_Structure
,	O
and	O
exists	O
in	O
a	O
namespace	O
identified	O
by	O
a	O
small-integer	O
namespace	O
identifier	O
.	O
</s>
<s>
In	O
Linux	B-Application
,	O
the	O
ext2	B-Application
,	O
ext3	B-Application
,	O
ext4	B-Application
,	O
JFS	B-Application
,	O
Squashfs	B-Application
,	O
UBIFS	B-Application
,	O
Yaffs2	B-Application
,	O
ReiserFS	B-Application
,	O
Reiser4	B-Application
,	O
XFS	B-Application
,	O
Btrfs	B-Operating_System
,	O
OrangeFS	B-Application
,	O
Lustre	B-Application
,	O
OCFS2	B-Application
1.6	I-Application
,	O
ZFS	B-Application
,	O
and	O
F2FS	B-Application
filesystems	B-Application
support	O
extended	B-Application
attributes	I-Application
(	O
abbreviated	O
xattr	B-Application
)	O
when	O
enabled	O
in	O
the	O
kernel	O
configuration	O
.	O
</s>
<s>
Any	O
regular	O
file	O
or	O
directory	O
may	O
have	O
extended	B-Application
attributes	I-Application
consisting	O
of	O
a	O
name	O
and	O
associated	O
data	O
.	O
</s>
<s>
The	O
name	O
must	O
be	O
a	O
null-terminated	B-Data_Structure
string	I-Data_Structure
prefixed	O
by	O
a	O
namespace	O
identifier	O
and	O
a	O
dot	O
character	O
.	O
</s>
<s>
The	O
security	O
namespace	O
is	O
used	O
by	O
SELinux	B-Application
,	O
for	O
example	O
.	O
</s>
<s>
Support	O
for	O
the	O
extended	B-Application
attribute	I-Application
concept	O
from	O
a	O
POSIX.1e	O
draft	O
that	O
had	O
been	O
withdrawn	O
in	O
1997	O
was	O
added	O
to	O
Linux	B-Application
around	O
2002	O
.	O
</s>
<s>
As	O
of	O
2016	O
,	O
they	O
are	O
not	O
yet	O
in	O
widespread	O
use	O
by	O
user-space	O
Linux	B-Application
programs	O
,	O
but	O
are	O
used	O
by	O
Beagle	B-Language
,	O
OpenStack	O
Swift	O
,	O
Dropbox	B-Application
,	O
KDE	B-Application
's	O
semantic	O
metadata	O
framework	O
(	O
Baloo	O
)	O
,	O
Chromium	B-Language
,	O
Wget	B-Protocol
and	O
cURL	B-Language
.	O
</s>
<s>
The	O
Linux	B-Application
kernel	O
allows	O
extended	B-Application
attribute	I-Application
to	O
have	O
names	O
of	O
up	O
to	O
255	O
bytes	O
and	O
values	O
of	O
up	O
to	O
64	O
KiB	O
,	O
</s>
<s>
as	O
do	O
XFS	B-Application
and	O
ReiserFS	B-Application
,	O
but	O
ext2/3/4	O
and	O
btrfs	B-Operating_System
impose	O
much	O
smaller	O
limits	O
,	O
requiring	O
all	O
the	O
attributes	O
(	O
names	O
and	O
values	O
)	O
of	O
one	O
file	O
to	O
fit	O
in	O
one	O
"	O
filesystem	B-Application
block	O
"	O
(	O
usually	O
4	B-Application
KiB	O
)	O
.	O
</s>
<s>
This	O
defines	O
the	O
four	O
namespaces	O
of	O
extended	B-Application
attributes	I-Application
.	O
</s>
<s>
Extended	B-Application
attributes	I-Application
can	O
be	O
accessed	O
and	O
modified	O
using	O
the	O
getfattr	O
and	O
setfattr	O
commands	O
from	O
the	O
attr	O
package	O
on	O
most	O
distributions	O
.	O
</s>
<s>
Mac	B-Application
OS	I-Application
X	I-Application
10.4	I-Application
and	O
later	O
support	O
extended	B-Application
attributes	I-Application
by	O
making	O
use	O
of	O
the	O
HFS+	B-Application
filesystem	B-Application
Attributes	O
File	O
B*	O
-tree	O
feature	O
which	O
allows	O
for	O
named	O
forks	B-Application
.	O
</s>
<s>
Although	O
the	O
named	O
forks	B-Application
in	O
HFS+	B-Application
support	O
arbitrarily	O
large	O
amounts	O
of	O
data	O
through	O
extents	O
,	O
the	O
OS	O
support	O
for	O
extended	B-Application
attributes	I-Application
only	O
supports	O
inline	O
attributes	O
,	O
limiting	O
their	O
size	O
to	O
that	O
which	O
can	O
fit	O
within	O
a	O
single	O
B*	O
-tree	O
node	O
.	O
</s>
<s>
Any	O
regular	O
file	O
may	O
have	O
a	O
list	O
of	O
extended	B-Application
attributes	I-Application
.	O
</s>
<s>
HFS+	B-Application
supports	O
an	O
arbitrary	O
number	O
of	O
named	O
forks	B-Application
,	O
and	O
it	O
is	O
unknown	O
if	O
macOS	B-Application
imposes	O
any	O
limit	O
on	O
the	O
number	O
of	O
extended	B-Application
attributes	I-Application
.	O
</s>
<s>
The	O
name	O
is	O
a	O
null-terminated	B-Data_Structure
Unicode	O
string	O
.	O
</s>
<s>
No	O
namespace	O
restrictions	O
are	O
present	O
(	O
making	O
this	O
an	O
open	O
xattr	B-Application
system	O
)	O
and	O
the	O
convention	O
is	O
to	O
use	O
a	O
reverse	O
DNS	O
string	O
(	O
similar	O
to	O
Uniform	B-Operating_System
Type	I-Operating_System
Identifiers	I-Operating_System
)	O
as	O
the	O
attribute	O
name	O
.	O
</s>
<s>
macOS	B-Application
supports	O
listing	O
,	O
getting	O
,	O
setting	O
,	O
and	O
removing	O
extended	B-Application
attributes	I-Application
from	O
files	O
or	O
directories	O
using	O
a	O
Linux-like	O
API	O
.	O
</s>
<s>
From	O
the	O
command	O
line	O
,	O
these	O
abilities	O
are	O
exposed	O
through	O
the	O
xattr	B-Application
utility	O
.	O
</s>
<s>
Since	O
macOS	B-Application
10.5	O
,	O
files	O
originating	O
from	O
the	O
web	O
are	O
marked	O
with	O
com.apple.quarantine	O
via	O
extended	B-Application
file	I-Application
attributes	I-Application
.	O
</s>
<s>
In	O
some	O
older	O
versions	O
of	O
macOS	B-Application
(	O
such	O
as	O
Mac	B-Device
OS	I-Device
X	I-Device
10.6	I-Device
)	O
,	O
user	O
space	O
extended	B-Application
attributes	I-Application
were	O
not	O
preserved	O
on	O
save	O
in	O
common	O
Cocoa	B-Operating_System
applications	O
(	O
TextEdit	O
,	O
Preview	O
etc	O
.	O
</s>
<s>
Support	O
for	O
extended	B-Application
file	I-Application
attributes	I-Application
was	O
removed	O
from	O
the	O
OpenBSD	B-Operating_System
source	O
code	O
in	O
2005	O
due	O
to	O
a	O
lack	O
of	O
interest	O
in	O
Access	O
Control	O
Lists	O
.	O
</s>
<s>
In	O
OS/2	B-Application
version	O
1.2	O
and	O
later	O
,	O
the	O
High	B-Application
Performance	I-Application
File	I-Application
System	I-Application
was	O
designed	O
with	O
extended	B-Application
attributes	I-Application
in	O
mind	O
,	O
but	O
support	O
for	O
them	O
was	O
also	O
retro-fitted	O
on	O
the	O
FAT	B-Application
filesystem	I-Application
of	O
DOS	O
.	O
</s>
<s>
For	O
compatibility	O
with	O
other	O
operating	O
systems	O
using	O
a	O
FAT	B-Application
partition	I-Application
,	O
OS/2	B-Application
attributes	O
are	O
stored	O
inside	O
a	O
single	O
file	O
""	O
located	O
in	O
the	O
root	O
directory	O
.	O
</s>
<s>
This	O
file	O
is	O
normally	O
inaccessible	O
when	O
an	O
operating	O
system	O
supporting	O
extended	B-Application
attributes	I-Application
manages	O
the	O
disk	O
,	O
but	O
can	O
be	O
freely	O
manipulated	O
under	O
,	O
for	O
example	O
,	O
DOS	O
.	O
</s>
<s>
Files	O
and	O
directories	O
having	O
extended	B-Application
attributes	I-Application
use	O
one	O
or	O
more	O
clusters	O
inside	O
this	O
file	O
.	O
</s>
<s>
These	O
two	O
bytes	O
are	O
used	O
for	O
other	O
purposes	O
on	O
the	O
FAT32	O
filesystem	B-Application
,	O
and	O
hence	O
OS/2	B-Application
extended	B-Application
attributes	I-Application
cannot	O
be	O
stored	O
on	O
this	O
filesystem	B-Application
.	O
</s>
<s>
Parts	O
of	O
OS/2	B-Application
version	O
2.0	O
and	O
later	O
such	O
as	O
the	O
Workplace	B-Device
Shell	I-Device
uses	O
several	O
standardized	O
extended	B-Application
attributes	I-Application
(	O
also	O
called	O
EAs	O
)	O
for	O
purposes	O
like	O
identifying	O
the	O
filetype	O
,	O
comments	O
,	O
computer	O
icons	O
and	O
keywords	O
about	O
the	O
file	O
.	O
</s>
<s>
Programs	O
written	O
in	O
the	O
interpreted	O
language	O
Rexx	B-Language
store	O
an	O
already	O
parsed	B-Language
version	O
of	O
the	O
code	O
as	O
an	O
extended	B-Application
attribute	I-Application
,	O
to	O
allow	O
faster	O
execution	O
.	O
</s>
<s>
Solaris	B-Application
version	O
9	O
and	O
later	O
allows	O
files	O
to	O
have	O
"	O
extended	B-Application
attributes	I-Application
"	O
,	O
which	O
are	O
actually	O
forks	B-Application
;	O
the	O
maximum	O
size	O
of	O
an	O
"	O
extended	B-Application
attribute	I-Application
"	O
is	O
the	O
same	O
as	O
the	O
maximum	O
size	O
of	O
a	O
file	O
,	O
and	O
they	O
are	O
read	O
and	O
written	O
in	O
the	O
same	O
fashion	O
as	O
files	O
.	O
</s>
<s>
Version	O
4	B-Application
of	O
the	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
supports	O
extended	B-Application
attributes	I-Application
in	O
much	O
the	O
same	O
way	O
as	O
Solaris	B-Application
.	O
</s>
<s>
On	O
Windows	B-Device
NT	I-Device
,	O
limited-length	O
extended	B-Application
attributes	I-Application
are	O
supported	O
by	O
FAT	B-Application
,	O
HPFS	B-Application
,	O
and	O
NTFS	B-Application
.	O
</s>
<s>
This	O
was	O
implemented	O
as	O
part	O
of	O
the	O
OS/2	B-Application
subsystem	O
.	O
</s>
<s>
They	O
are	O
notably	O
used	O
by	O
the	O
NFS	B-Protocol
server	O
of	O
the	O
Interix	B-Operating_System
POSIX	O
subsystem	O
in	O
order	O
to	O
implement	O
Unix-like	B-Operating_System
permissions	O
.	O
</s>
<s>
The	O
Windows	O
Subsystem	O
for	O
Linux	B-Application
added	O
in	O
the	O
Windows	O
10	O
Anniversary	O
Update	O
uses	O
them	O
for	O
similar	O
purposes	O
,	O
storing	O
the	O
Linux	B-Application
file	O
mode	O
,	O
owner	O
,	O
device	O
ID	O
(	O
if	O
applicable	O
)	O
,	O
and	O
file	B-Application
times	I-Application
in	O
the	O
extended	B-Application
attributes	I-Application
.	O
</s>
<s>
Additionally	O
,	O
NTFS	B-Application
can	O
store	O
arbitrary-length	O
extended	B-Application
attributes	I-Application
in	O
the	O
form	O
of	O
alternate	O
data	O
streams	O
(	O
ADS	O
)	O
,	O
a	O
type	O
of	O
resource	B-Application
fork	I-Application
.	O
</s>
<s>
Plugins	O
for	O
the	O
file	O
manager	O
Total	B-Language
Commander	I-Language
,	O
like	O
NTFS	B-Application
Descriptions	O
and	O
QuickSearch	O
eXtended	O
support	O
filtering	O
the	O
file	O
list	O
by	O
or	O
searching	O
for	O
metadata	O
contained	O
in	O
ADS	O
.	O
</s>
<s>
NTFS-3G	B-Application
supports	O
mapping	O
ADS	O
to	O
extended	B-Application
attributes	I-Application
in	O
FUSE	B-Application
;	O
it	O
also	O
maps	O
file	B-Application
attributes	I-Application
that	O
way	O
.	O
</s>
