<s>
The	O
Filesystem	B-Application
Hierarchy	I-Application
Standard	I-Application
(	O
FHS	O
)	O
is	O
a	O
reference	O
describing	O
the	O
conventions	O
used	O
for	O
the	O
layout	O
of	O
a	O
UNIX	O
system	O
.	O
</s>
<s>
It	O
has	O
been	O
made	O
popular	O
by	O
its	O
use	O
in	O
Linux	B-Application
distributions	I-Application
,	O
but	O
it	O
is	O
used	O
by	O
other	O
UNIX	O
variants	O
as	O
well	O
.	O
</s>
<s>
It	O
is	O
maintained	O
by	O
the	B-Operating_System
Linux	I-Operating_System
Foundation	I-Operating_System
.	O
</s>
<s>
In	O
the	O
FHS	O
,	O
all	O
files	O
and	O
directories	B-Application
appear	O
under	O
the	O
root	B-Application
directory	I-Application
/	O
,	O
even	O
if	O
they	O
are	O
stored	O
on	O
different	O
physical	O
or	O
virtual	O
devices	O
.	O
</s>
<s>
Some	O
of	O
these	O
directories	B-Application
only	O
exist	O
on	O
a	O
particular	O
system	O
if	O
certain	O
subsystems	O
,	O
such	O
as	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
,	O
are	O
installed	O
.	O
</s>
<s>
Most	O
of	O
these	O
directories	B-Application
exist	O
in	O
all	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
and	O
are	O
generally	O
used	O
in	O
much	O
the	O
same	O
way	O
;	O
however	O
,	O
the	O
descriptions	O
here	O
are	O
those	O
used	O
specifically	O
for	O
the	O
FHS	O
and	O
are	O
not	O
considered	O
authoritative	O
for	O
platforms	O
other	O
than	O
Linux	O
.	O
</s>
<s>
DirectoryDescription/Primary	O
hierarchy	O
root	B-Application
and	O
root	B-Application
directory	I-Application
of	O
the	O
entire	O
file	B-Application
system	I-Application
hierarchy./binEssential	O
command	O
binaries	B-Application
that	O
need	O
to	O
be	O
available	O
in	O
single-user	B-Operating_System
mode	I-Operating_System
,	O
including	O
to	O
bring	O
up	O
the	O
system	O
or	O
repair	O
it	O
,	O
for	O
all	O
users	O
(	O
e.g.	O
,	O
cat	B-Device
,	O
ls	B-Application
,	O
cp	B-Application
)	O
./bootBoot	O
loader	O
files	O
(	O
e.g.	O
,	O
kernels	B-Operating_System
,	O
initrd	B-Application
)	O
./devDevice	O
files	O
(	O
e.g.	O
,	O
/dev/null	B-Operating_System
,	O
/dev/disk0	O
,	O
/dev/sda1	O
,	O
/dev/tty	O
,	O
%2Fdev%2Frandom	O
)	O
./etcHost	O
-specific	O
system-wide	O
configuration	B-Protocol
files	I-Protocol
.	O
</s>
<s>
In	O
early	O
versions	O
of	O
the	O
UNIX	O
Implementation	O
Document	O
from	O
Bell	O
labs	O
,	O
/etc	O
is	O
referred	O
to	O
as	O
the	O
etcetera	O
directory	B-Application
,	O
as	O
this	O
directory	B-Application
historically	O
held	O
everything	O
that	O
did	O
not	O
belong	O
elsewhere	O
(	O
however	O
,	O
the	O
FHS	O
restricts	O
/etc	O
to	O
static	O
configuration	B-Protocol
files	I-Protocol
and	O
may	O
not	O
contain	O
binaries	B-Application
)	O
.	O
</s>
<s>
Since	O
the	O
publication	O
of	O
early	O
documentation	O
,	O
the	O
directory	B-Application
name	O
has	O
been	O
re-explained	O
in	O
various	O
ways	O
.	O
</s>
<s>
Recent	O
interpretations	O
include	O
backronyms	O
such	O
as	O
"	O
Editable	O
Text	O
Configuration	O
"	O
or	O
"	O
Extended	O
Tool	O
Chest	O
"	O
.Define	O
-	O
/etc	O
?,	O
Posted	O
by	O
Cliff	O
,	O
3	O
March	O
2007	O
-	O
Slashdot./etc/optConfiguration	O
files	O
for	O
add-on	O
packages	B-Application
stored	O
in	O
/opt./etc/sgmlConfiguration	O
files	O
,	O
such	O
as	O
catalogs	O
,	O
for	O
software	O
that	O
processes	O
SGML./etc/X11Configuration	O
files	O
for	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
,	O
version	O
11./etc/xmlConfiguration	O
files	O
,	O
such	O
as	O
catalogs	O
,	O
for	O
software	O
that	O
processes	O
XML./homeUsers	O
'	O
home	B-Application
directories	I-Application
,	O
containing	O
saved	O
files	O
,	O
personal	O
settings	O
,	O
etc./libLibraries	O
essential	O
for	O
the	O
binaries	B-Application
in	O
/bin	O
and	O
/sbin./lib	O
<	O
qual>Alternate	O
format	O
essential	O
libraries	B-Library
.	O
</s>
<s>
These	O
are	O
typically	O
used	O
on	O
systems	O
that	O
support	O
more	O
than	O
one	O
executable	B-Application
code	I-Application
format	O
,	O
such	O
as	O
systems	O
supporting	O
32-bit	O
and	O
64-bit	B-Device
versions	O
of	O
an	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
Such	O
directories	B-Application
are	O
optional	O
,	O
but	O
if	O
they	O
exist	O
,	O
they	O
have	O
some	O
requirements./mediaMount	O
points	O
for	O
removable	B-Device
media	I-Device
such	O
as	O
CD-ROMs	B-Device
(	O
appeared	O
in	O
FHS-2.3	O
in	O
2004	O
)	O
./mntTemporarily	O
mounted	B-Application
filesystems./optAdd	O
-on	O
application	B-Application
software	I-Application
packages./procVirtual	O
filesystem	B-Application
providing	O
process	B-Operating_System
and	O
kernel	B-Operating_System
information	O
as	O
files	O
.	O
</s>
<s>
In	O
Linux	O
,	O
corresponds	O
to	O
a	O
procfs	B-Application
mount	O
.	O
</s>
<s>
Generally	O
,	O
automatically	O
generated	O
and	O
populated	O
by	O
the	O
system	O
,	O
on	O
the	O
fly./rootHome	O
directory	B-Application
for	O
the	O
root	O
user./runRun	O
-time	O
variable	O
data	O
:	O
Information	O
about	O
the	O
running	O
system	O
since	O
last	O
boot	O
,	O
e.g.	O
,	O
currently	O
logged-in	O
users	O
and	O
running	O
daemons	B-Operating_System
.	O
</s>
<s>
Files	O
under	O
this	O
directory	B-Application
must	O
be	O
either	O
removed	O
or	O
truncated	O
at	O
the	O
beginning	O
of	O
the	O
boot	O
process	B-Operating_System
,	O
but	O
this	O
is	O
not	O
necessary	O
on	O
systems	O
that	O
provide	O
this	O
directory	B-Application
as	O
a	O
temporary	B-Application
filesystem	I-Application
(	O
tmpfs	B-Application
)	O
./sbinEssential	O
system	O
binaries	B-Application
(	O
e.g.	O
,	O
fsck	B-Device
,	O
init	B-Operating_System
,	O
route	B-Protocol
)	O
./srvSite	O
-specific	O
data	O
served	O
by	O
this	O
system	O
,	O
such	O
as	O
data	O
and	O
scripts	O
for	O
web	O
servers	O
,	O
data	O
offered	O
by	O
FTP	B-Protocol
servers	I-Protocol
,	O
and	O
repositories	O
for	O
version	B-Architecture
control	I-Architecture
systems	I-Architecture
(	O
appeared	O
in	O
FHS-2.3	O
in	O
2004	O
)	O
./sysContains	O
information	O
about	O
devices	O
,	O
drivers	O
,	O
and	O
some	O
kernel	B-Operating_System
features./tmpDirectory	O
for	O
temporary	O
files	O
(	O
see	O
also	O
/var/tmp	O
)	O
.	O
</s>
<s>
/usrSecondary	O
hierarchy	O
for	O
read-only	O
user	O
data	O
;	O
contains	O
the	O
majority	O
of	O
(	O
multi	B-Operating_System
-	I-Operating_System
)	O
user	O
utilities	O
and	O
applications	O
.	O
</s>
<s>
Should	O
be	O
shareable	O
and	O
read-only./usr/binNon	O
-essential	O
command	O
binaries	B-Application
(	O
not	O
needed	O
in	O
single-user	B-Operating_System
mode	I-Operating_System
)	O
;	O
for	O
all	O
users./usr/includeStandard	O
include	O
files./usr/libLibraries	O
for	O
the	O
binaries	B-Application
in	O
/usr/bin	O
and	O
/usr/sbin./usr/libexecBinaries	O
run	O
by	O
other	O
programs	O
that	O
are	O
not	O
intended	O
to	O
be	O
executed	O
directly	O
by	O
users	O
or	O
shell	O
scripts	O
(	O
optional	O
)	O
./usr/lib	O
<	O
qual>Alternative-format	O
libraries	B-Library
(	O
e.g.	O
,	O
/usr/lib32	O
for	O
32-bit	O
libraries	B-Library
on	O
a	O
64-bit	B-Device
machine	O
(	O
optional	O
)	O
)	O
./usr/localTertiary	O
hierarchy	O
for	O
local	O
data	O
,	O
specific	O
to	O
this	O
host	O
.	O
</s>
<s>
Typically	O
has	O
further	O
subdirectories	B-Application
(	O
e.g.	O
,	O
bin	O
,	O
lib	O
,	O
share	O
)	O
.Historically	O
and	O
strictly	O
according	O
to	O
the	O
standard	O
,	O
/usr/local	O
is	O
for	O
data	O
that	O
must	O
be	O
stored	O
on	O
the	O
local	O
host	O
(	O
as	O
opposed	O
to	O
/usr	O
,	O
which	O
may	O
be	O
mounted	B-Application
across	O
a	O
network	O
)	O
.	O
</s>
<s>
It	O
is	O
possible	O
that	O
the	O
FHS	O
standard	O
may	O
in	O
the	O
future	O
be	O
changed	O
to	O
reflect	O
this	O
de	O
facto	O
convention./usr/sbinNon	O
-essential	O
system	O
binaries	B-Application
(	O
e.g.	O
,	O
daemons	B-Operating_System
for	O
various	O
network	B-General_Concept
services	I-General_Concept
)	O
./usr/shareArchitecture	O
-independent	O
(	O
shared	O
)	O
data./usr/srcSource	O
code	O
(	O
e.g.	O
,	O
the	O
kernel	B-Operating_System
source	O
code	O
with	O
its	O
header	B-Language
files	I-Language
)	O
./usr/X11R6X	O
Window	O
System	O
,	O
Version	O
11	O
,	O
Release	O
6	O
(	O
up	O
to	O
FHS-2.3	O
,	O
optional	O
)	O
./varVariable	O
files	O
:	O
files	O
whose	O
content	O
is	O
expected	O
to	O
continually	O
change	O
during	O
normal	O
operation	O
of	O
the	O
system	O
,	O
such	O
as	O
logs	O
,	O
spool	B-Device
files	O
,	O
and	O
temporary	O
e-mail	O
files./var/cacheApplication	O
cache	O
data	O
.	O
</s>
<s>
In	O
some	O
distributions	O
,	O
these	O
files	O
may	O
be	O
located	O
in	O
the	O
deprecated	B-General_Concept
/var/spool/mail./var/optVariable	O
data	O
from	O
add-on	O
packages	B-Application
that	O
are	O
stored	O
in	O
/opt./var/runRun	O
-time	O
variable	O
data	O
.	O
</s>
<s>
This	O
directory	B-Application
contains	O
system	O
information	O
data	O
describing	O
the	O
system	O
since	O
it	O
was	O
booted	O
.	O
</s>
<s>
In	O
FHS	O
3.0	O
,	O
/var/run	O
is	O
replaced	O
by	O
/run	B-Application
;	O
a	O
system	O
should	O
either	O
continue	O
to	O
provide	O
a	O
/var/run	O
directory	B-Application
or	O
provide	O
a	O
symbolic	B-Application
link	I-Application
from	O
/var/run	O
to	O
/run	B-Application
for	O
backwards	O
compatibility./var/spoolSpool	O
for	O
tasks	O
waiting	O
to	O
be	O
processed	O
(	O
e.g.	O
,	O
print	O
queues	B-Device
and	O
outgoing	O
mail	O
queue	B-Device
)	O
./var/spool/mailDeprecated	O
location	O
for	O
users	O
 '	O
mailboxes	O
.	O
</s>
<s>
Most	O
Linux	B-Application
distributions	I-Application
follow	O
the	O
Filesystem	B-Application
Hierarchy	I-Application
Standard	I-Application
and	O
declare	O
it	O
their	O
own	O
policy	O
to	O
maintain	O
FHS	O
compliance	O
.	O
</s>
<s>
GoboLinux	O
and	O
NixOS	O
provide	O
examples	O
of	O
intentionally	O
non-compliant	O
filesystem	B-Application
implementations	O
.	O
</s>
<s>
Modern	O
Linux	B-Application
distributions	I-Application
include	O
a	O
/sys	B-Application
directory	B-Application
as	O
a	O
virtual	B-Application
filesystem	I-Application
(	O
sysfs	B-Application
,	O
comparable	O
to	O
/proc	B-Application
,	O
which	O
is	O
a	O
procfs	B-Application
)	O
,	O
which	O
stores	O
and	O
allows	O
modification	O
of	O
the	O
devices	O
connected	O
to	O
the	O
system	O
,	O
whereas	O
many	O
traditional	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
use	O
/sys	B-Application
as	O
a	O
symbolic	B-Application
link	I-Application
to	O
the	O
kernel	B-Operating_System
source	O
tree	O
.	O
</s>
<s>
Many	O
modern	O
Unix-like	B-Operating_System
systems	I-Operating_System
(	O
like	O
FreeBSD	B-Operating_System
via	O
its	O
ports	B-Application
system	O
)	O
install	O
third-party	O
packages	B-Application
into	O
/usr/local	O
,	O
while	O
keeping	O
code	O
considered	O
part	O
of	O
the	O
operating	O
system	O
in	O
/usr	O
.	O
</s>
<s>
Some	O
Linux	B-Application
distributions	I-Application
no	O
longer	O
differentiate	O
between	O
/lib	O
and	O
/usr/lib	O
and	O
have	O
/lib	O
symlinked	O
to	O
/usr/lib	O
.	O
</s>
<s>
Some	O
Linux	B-Application
distributions	I-Application
no	O
longer	O
differentiate	O
between	O
/bin	O
and	O
/usr/bin	O
and	O
between	O
/sbin	O
and	O
/usr/sbin	B-Application
.	O
</s>
<s>
They	O
may	O
symlink	B-Application
/bin	O
to	O
/usr/bin	O
and	O
/sbin	O
to	O
/usr/sbin	B-Application
.	O
</s>
<s>
Modern	O
Linux	B-Application
distributions	I-Application
include	O
a	O
/run	B-Application
directory	B-Application
as	O
a	O
temporary	B-Application
filesystem	I-Application
(	O
tmpfs	B-Application
)	O
,	O
which	O
stores	O
volatile	O
runtime	O
data	O
,	O
following	O
the	O
FHS	O
version	O
3.0	O
.	O
</s>
<s>
According	O
to	O
the	O
FHS	O
version	O
2.3	O
,	O
such	O
data	O
were	O
stored	O
in	O
/var/run	O
,	O
but	O
this	O
was	O
a	O
problem	O
in	O
some	O
cases	O
because	O
this	O
directory	B-Application
is	O
not	O
always	O
available	O
at	O
early	O
boot	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
these	O
programs	O
have	O
had	O
to	O
resort	O
to	O
trickery	O
,	O
such	O
as	O
using	O
/dev/.udev	O
,	O
/dev/.mdadm	O
,	O
/dev/.systemd	O
or	O
/dev/.mount	O
directories	B-Application
,	O
even	O
though	O
the	O
device	O
directory	B-Application
is	O
not	O
intended	O
for	O
such	O
data	O
.	O
</s>
<s>
Among	O
other	O
advantages	O
,	O
this	O
makes	O
the	O
system	O
easier	O
to	O
use	O
normally	O
with	O
the	O
root	B-Application
filesystem	I-Application
mounted	B-Application
read-only	O
.	O
</s>
<s>
/dev/	B-Application
.	O
</s>
<s>
FHS	O
was	O
created	O
as	O
the	O
FSSTND	B-Application
(	O
short	O
for	O
"	O
Filesystem	B-Application
Standard	O
"	O
)	O
,	O
largely	O
based	O
on	O
similar	O
standards	O
for	O
other	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
Notable	O
examples	O
are	O
these	O
:	O
the	O
description	O
of	O
file	B-Application
system	I-Application
layout	O
,	O
which	O
has	O
existed	O
since	O
the	O
release	O
of	O
Version	B-Operating_System
7	I-Operating_System
Unix	I-Operating_System
(	O
in	O
1979	O
)	O
;	O
the	O
SunOS	B-Operating_System
and	O
its	O
successor	O
,	O
the	O
Solaris	B-Application
.	O
</s>
<s>
Version	O
Release	O
date	O
Notes	O
1994-02-14	O
FSSTND	B-Application
1994-10-09	O
FSSTND	B-Application
1995-03-28	O
FSSTND	B-Application
1997-10-26	O
FHS	O
2.0	O
is	O
the	O
direct	O
successor	O
for	O
FSSTND	B-Application
1.2	O
.	O
</s>
