<s>
In	O
Unix	B-Application
and	O
operating	B-General_Concept
systems	I-General_Concept
inspired	O
by	O
it	O
,	O
the	O
file	B-Application
system	I-Application
is	O
considered	O
a	O
central	O
component	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
It	O
was	O
also	O
one	O
of	O
the	O
first	O
parts	O
of	O
the	O
system	O
to	O
be	O
designed	O
and	O
implemented	O
by	O
Ken	O
Thompson	O
in	O
the	O
first	O
experimental	O
version	O
of	O
Unix	B-Application
,	O
dated	B-Operating_System
1969	I-Operating_System
.	O
</s>
<s>
As	O
in	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
the	O
filesystem	B-Application
provides	O
information	O
storage	O
and	O
retrieval	O
,	O
and	O
one	O
of	O
several	O
forms	O
of	O
interprocess	B-Operating_System
communication	I-Operating_System
,	O
in	O
that	O
the	O
many	O
small	O
programs	O
that	O
traditionally	O
form	O
a	O
Unix	B-Application
system	I-Application
can	O
store	O
information	O
in	O
files	O
so	O
that	O
other	O
programs	O
can	O
read	O
them	O
,	O
although	O
pipes	B-Operating_System
complemented	O
it	O
in	O
this	O
role	O
starting	O
with	O
the	O
Third	B-Operating_System
Edition	I-Operating_System
.	O
</s>
<s>
Also	O
,	O
the	O
filesystem	B-Application
provides	O
access	O
to	O
other	O
resources	O
through	O
so-called	O
device	B-Application
files	I-Application
that	O
are	O
entry	O
points	O
to	O
terminals	B-General_Concept
,	O
printers	O
,	O
and	O
mice	B-Device
.	O
</s>
<s>
The	O
rest	O
of	O
this	O
article	O
uses	O
Unix	B-Application
as	O
a	O
generic	O
name	O
to	O
refer	O
to	O
both	O
the	O
original	O
Unix	B-Application
operating	I-Application
system	I-Application
and	O
its	O
many	O
workalikes	B-Operating_System
.	O
</s>
<s>
The	O
filesystem	B-Application
appears	O
as	O
one	O
rooted	O
tree	O
of	O
directories	B-Application
.	O
</s>
<s>
Instead	O
of	O
addressing	O
separate	O
volumes	O
such	O
as	O
disk	B-Application
partitions	I-Application
,	O
removable	O
media	O
,	O
and	O
network	B-General_Concept
shares	I-General_Concept
as	O
separate	O
trees	O
(	O
as	O
done	O
in	O
DOS	B-Device
and	O
Windows	B-Application
:	O
each	O
drive	O
has	O
a	O
drive	O
letter	O
that	O
denotes	O
the	O
root	O
of	O
its	O
file	B-Application
system	I-Application
tree	O
)	O
,	O
such	O
volumes	O
can	O
be	O
mounted	B-Device
on	O
a	O
directory	B-Application
,	O
causing	O
the	O
volume	O
's	O
file	B-Application
system	I-Application
tree	O
to	O
appear	O
as	O
that	O
directory	B-Application
in	O
the	O
larger	O
tree	O
.	O
</s>
<s>
In	O
the	O
original	O
Bell	B-Operating_System
Labs	I-Operating_System
Unix	I-Operating_System
,	O
a	O
two-disk	O
setup	O
was	O
customary	O
,	O
where	O
the	O
first	O
disk	O
contained	O
startup	O
programs	O
,	O
while	O
the	O
second	O
contained	O
users	O
 '	O
files	O
and	O
programs	O
.	O
</s>
<s>
This	O
second	O
disk	O
was	O
mounted	B-Device
at	O
the	O
empty	O
directory	B-Application
named	O
usr	O
on	O
the	O
first	O
disk	O
,	O
causing	O
the	O
two	O
disks	O
to	O
appear	O
as	O
one	O
filesystem	B-Application
,	O
with	O
the	O
second	O
disk	O
’s	O
contents	O
viewable	O
at	O
/usr	O
.	O
</s>
<s>
Unix	B-Application
directories	B-Application
do	O
not	O
contain	O
files	O
.	O
</s>
<s>
Instead	O
,	O
they	O
contain	O
the	O
names	O
of	O
files	O
paired	O
with	O
references	O
to	O
so-called	O
inodes	B-Application
,	O
which	O
in	O
turn	O
contain	O
both	O
the	O
file	O
and	O
its	O
metadata	O
(	O
owner	O
,	O
permissions	O
,	O
time	O
of	O
last	O
access	O
,	O
etc.	O
,	O
but	O
no	O
name	O
)	O
.	O
</s>
<s>
Multiple	O
names	O
in	O
the	O
file	B-Application
system	I-Application
may	O
refer	O
to	O
the	O
same	O
file	O
,	O
a	O
feature	O
termed	O
a	O
hard	B-Application
link	I-Application
.	O
</s>
<s>
The	O
mathematical	O
traits	O
of	O
hard	B-Application
links	I-Application
make	O
the	O
file	B-Application
system	I-Application
a	O
limited	O
type	O
of	O
directed	O
acyclic	O
graph	O
,	O
although	O
the	O
directories	B-Application
still	O
form	O
a	O
tree	O
,	O
as	O
they	O
typically	O
may	O
not	O
be	O
hard-linked	B-Application
.	O
</s>
<s>
(	O
As	O
originally	O
envisioned	O
in	O
1969	O
,	O
the	O
Unix	B-Operating_System
file	I-Operating_System
system	I-Operating_System
would	O
in	O
fact	O
be	O
used	O
as	O
a	O
general	O
graph	O
with	O
hard	B-Application
links	I-Application
to	O
directories	B-Application
providing	O
navigation	O
,	O
instead	O
of	O
path	O
names	O
.	O
)	O
</s>
<s>
The	O
original	O
Unix	B-Operating_System
file	I-Operating_System
system	I-Operating_System
supported	O
three	O
types	O
of	O
files	O
:	O
ordinary	O
files	O
,	O
directories	B-Application
,	O
and	O
"	O
special	B-Application
files	I-Application
"	O
,	O
also	O
termed	O
device	B-Application
files	I-Application
.	O
</s>
<s>
The	O
Berkeley	B-Operating_System
Software	I-Operating_System
Distribution	I-Operating_System
(	O
BSD	B-Operating_System
)	O
and	O
System	B-Operating_System
V	I-Operating_System
each	O
added	O
a	O
file	O
type	O
to	O
be	O
used	O
for	O
interprocess	B-Operating_System
communication	I-Operating_System
:	O
BSD	B-Operating_System
added	O
sockets	B-Protocol
,	O
while	O
System	B-Operating_System
V	I-Operating_System
added	O
FIFO	O
files	O
.	O
</s>
<s>
BSD	B-Operating_System
also	O
added	O
symbolic	B-Application
links	I-Application
(	O
often	O
termed	O
"	O
symlinks	B-Application
"	O
)	O
to	O
the	O
range	O
of	O
file	O
types	O
,	O
which	O
are	O
files	O
that	O
refer	O
to	O
other	O
files	O
,	O
and	O
complement	O
hard	B-Application
links	I-Application
.	O
</s>
<s>
Symlinks	B-Application
were	O
modeled	O
after	O
a	O
similar	O
feature	O
in	O
Multics	B-Application
,	O
and	O
differ	O
from	O
hard	B-Application
links	I-Application
in	O
that	O
they	O
may	O
span	O
filesystems	B-Application
and	O
that	O
their	O
existence	O
is	O
independent	O
of	O
the	O
target	O
object	O
.	O
</s>
<s>
Other	O
Unix	B-Application
systems	I-Application
may	O
support	O
additional	O
types	O
of	O
files	O
.	O
</s>
<s>
Certain	O
conventions	O
exist	O
for	O
locating	O
some	O
kinds	O
of	O
files	O
,	O
such	O
as	O
programs	O
,	O
system	O
configuration	O
files	O
,	O
and	O
users	O
 '	O
home	B-Application
directories	I-Application
.	O
</s>
<s>
These	O
were	O
first	O
documented	O
in	O
the	O
hier(7 )	O
man	B-Protocol
page	I-Protocol
since	O
Version	B-Operating_System
7	I-Operating_System
Unix	I-Operating_System
;	O
subsequent	O
versions	O
,	O
derivatives	O
and	O
clones	O
typically	O
have	O
a	O
similar	O
man	B-Protocol
page	I-Protocol
.	O
</s>
<s>
The	O
details	O
of	O
the	O
directory	B-Application
layout	O
have	O
varied	O
over	O
time	O
.	O
</s>
<s>
Although	O
the	O
file	B-Application
system	I-Application
layout	O
is	O
not	O
part	O
of	O
the	O
Single	O
UNIX	B-Application
Specification	O
,	O
several	O
attempts	O
exist	O
to	O
standardize	O
(	O
parts	O
of	O
)	O
it	O
,	O
such	O
as	O
the	O
System	B-Operating_System
V	I-Operating_System
Application	B-Operating_System
Binary	I-Operating_System
Interface	I-Operating_System
,	O
the	O
Intel	B-Operating_System
Binary	I-Operating_System
Compatibility	I-Operating_System
Standard	I-Operating_System
,	O
the	O
Common	O
Operating	B-General_Concept
System	I-General_Concept
Environment	O
,	O
and	O
Linux	B-Operating_System
Foundation	I-Operating_System
's	O
Filesystem	B-Application
Hierarchy	I-Application
Standard	I-Application
(	O
FHS	O
)	O
.	O
</s>
<s>
Here	O
is	O
a	O
generalized	O
overview	O
of	O
common	O
locations	O
of	O
files	O
on	O
a	O
Unix	B-Application
operating	I-Application
system	I-Application
:	O
</s>
<s>
Directory	B-Application
or	O
fileDescription/The	O
slash	O
/	O
character	O
alone	O
denotes	O
the	O
root	O
of	O
the	O
filesystem	B-Application
tree./binStands	O
for	O
binaries	B-Application
and	O
contains	O
certain	O
fundamental	O
utilities	O
,	O
such	O
as	O
ls	O
or	O
cp	O
,	O
that	O
are	O
needed	O
to	O
mount	O
/usr	O
,	O
when	O
that	O
is	O
a	O
separate	O
filesystem	B-Application
,	O
or	O
to	O
run	O
in	O
one-user	O
(	O
administrative	O
)	O
mode	O
when	O
/usr	O
cannot	O
be	O
mounted	B-Device
.	O
</s>
<s>
In	O
System	B-Operating_System
V.4	I-Operating_System
,	O
this	O
is	O
a	O
symlink	B-Application
to	O
/usr/bin	O
.	O
</s>
<s>
Otherwise	O
,	O
it	O
needs	O
to	O
be	O
on	O
the	O
root	O
filesystem	B-Application
itself./bootContains	O
all	O
the	O
files	O
needed	O
for	O
successful	O
booting	O
process	O
.	O
</s>
<s>
In	O
Research	B-Operating_System
Unix	I-Operating_System
,	O
this	O
was	O
one	O
file	O
rather	O
than	O
a	O
directory	B-Application
.	O
</s>
<s>
Nowadays	O
usually	O
on	O
the	O
root	O
filesystem	B-Application
itself	O
,	O
unless	O
the	O
system	O
,	O
bootloader	O
etc	O
.	O
</s>
<s>
Contains	O
file	B-Application
representations	I-Application
of	O
peripheral	O
devices	O
and	O
pseudo-devices	O
.	O
</s>
<s>
Needs	O
to	O
be	O
on	O
the	O
root	O
filesystem	B-Application
itself./etcContains	O
system-wide	O
configuration	O
files	O
and	O
system	O
databases	O
;	O
the	O
name	O
stands	O
for	O
et	O
cetera	O
but	O
now	O
a	O
better	O
expansion	O
is	O
editable-text-configurations	O
.	O
</s>
<s>
Needs	O
to	O
be	O
on	O
the	O
root	O
filesystem	B-Application
itself./homeContains	O
user	O
home	B-Application
directories	I-Application
on	O
Linux	O
and	O
some	O
other	O
systems	O
.	O
</s>
<s>
In	O
the	O
original	O
version	O
of	O
Unix	B-Application
,	O
home	B-Application
directories	I-Application
were	O
in	O
/usr	O
instead	O
.	O
</s>
<s>
Some	O
systems	O
use	O
or	O
have	O
used	O
different	O
locations	O
still	O
:	O
macOS	B-Application
has	O
home	B-Application
directories	I-Application
in	O
/Users	O
,	O
older	O
versions	O
of	O
BSD	B-Operating_System
put	O
them	O
in	O
/u	O
,	O
FreeBSD	B-Operating_System
has	O
/usr/home./libOriginally	O
essential	O
libraries	O
:	O
C	B-Language
libraries	O
,	O
but	O
not	O
Fortran	B-Application
ones	O
.	O
</s>
<s>
On	O
modern	O
systems	O
,	O
it	O
contains	O
the	O
shared	O
libraries	O
needed	O
by	O
programs	O
in	O
/bin	O
,	O
and	O
possibly	O
loadable	B-Application
kernel	I-Application
module	I-Application
or	O
device	B-Application
drivers	I-Application
.	O
</s>
<s>
Linux	B-Application
distributions	I-Application
may	O
have	O
variants	O
/lib32	O
and	O
/lib64	O
for	O
multi-architecture	O
support./mediaDefault	O
mount	O
point	O
for	O
removable	O
devices	O
,	O
such	O
as	O
USB	O
sticks	O
,	O
media	O
players	O
,	O
etc	O
.	O
</s>
<s>
By	O
common	O
sense	O
,	O
the	O
directory	B-Application
itself	O
,	O
whose	O
subdirectories	B-Application
are	O
mountpoints	O
,	O
is	O
on	O
the	O
root	O
partition	B-Application
itself./mntStands	O
for	O
mount	O
.	O
</s>
<s>
Empty	O
directory	B-Application
commonly	O
used	O
by	O
system	O
administrators	O
as	O
a	O
temporary	O
mount	O
point	O
.	O
</s>
<s>
By	O
common	O
sense	O
,	O
the	O
directory	B-Application
itself	O
,	O
whose	O
subdirectories	B-Application
are	O
mountpoints	O
,	O
is	O
on	O
the	O
root	O
partition	B-Application
itself./optContains	O
locally	O
installed	O
software	O
.	O
</s>
<s>
Originated	O
in	O
System	B-Operating_System
V	I-Operating_System
,	O
which	O
has	O
a	O
package	B-Application
manager	I-Application
that	O
installs	O
software	O
to	O
this	O
directory	B-Application
(	O
one	O
subdirectory	B-Application
per	O
package	O
)	O
.System	O
V	O
Application	B-Operating_System
Binary	I-Operating_System
Interface	I-Operating_System
Edition	O
4.1	O
(	O
1997-03-18	O
)	O
/procprocfs	O
virtual	O
filesystem	B-Application
showing	O
information	O
about	O
processes	B-Operating_System
as	O
files./rootThe	O
home	B-Application
directory	I-Application
for	O
the	O
superuser	B-Application
root	O
-	O
that	O
is	O
,	O
the	O
system	O
administrator	O
.	O
</s>
<s>
This	O
account	O
's	O
home	B-Application
directory	I-Application
is	O
usually	O
on	O
the	O
initial	O
filesystem	B-Application
,	O
and	O
hence	O
not	O
in	O
/home	B-Application
(	O
which	O
may	O
be	O
a	O
mount	O
point	O
for	O
another	O
filesystem	B-Application
)	O
in	O
case	O
specific	O
maintenance	O
needs	O
to	O
be	O
performed	O
,	O
during	O
which	O
other	O
filesystems	B-Application
are	O
not	O
available	O
.	O
</s>
<s>
Such	O
a	O
case	O
could	O
occur	O
,	O
for	O
example	O
,	O
if	O
a	O
hard	O
disk	O
drive	O
suffers	O
failures	O
and	O
cannot	O
be	O
properly	O
mounted	B-Device
.	O
</s>
<s>
By	O
convention	O
,	O
this	O
directory	B-Application
is	O
on	O
the	O
root	O
partition	B-Application
itself	O
;	O
in	O
any	O
case	O
,	O
it	O
is	O
not	O
a	O
link	O
to	O
/home/root	O
or	O
any	O
such	O
thing./sbinStands	O
for	O
"	O
system	O
(	O
or	O
superuser	B-Application
)	O
binaries	B-Application
"	O
and	O
contains	O
fundamental	O
utilities	O
,	O
such	O
as	O
init	O
,	O
usually	O
needed	O
to	O
start	O
,	O
maintain	O
and	O
recover	O
the	O
system	O
.	O
</s>
<s>
Needs	O
to	O
be	O
on	O
the	O
root	O
partition	B-Application
itself./srvServer	O
data	O
(	O
data	O
for	O
services	O
provided	O
by	O
system	O
)	O
./sysIn	O
some	O
Linux	B-Application
distributions	I-Application
,	O
contains	O
a	O
sysfs	B-Application
virtual	O
filesystem	B-Application
,	O
containing	O
information	O
related	O
to	O
hardware	O
and	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
On	O
BSD	B-Operating_System
systems	O
,	O
commonly	O
a	O
symlink	B-Application
to	O
the	O
kernel	B-Operating_System
sources	O
in	O
/usr/src/sys./tmpA	O
place	O
for	O
temporary	O
files	O
not	O
expected	O
to	O
survive	O
a	O
reboot	O
.	O
</s>
<s>
Many	O
systems	O
clear	O
this	O
directory	B-Application
upon	O
startup	O
or	O
use	O
tmpfs	B-Application
to	O
implement	O
it./unixThe	O
Unix	B-Application
kernel	B-Operating_System
in	O
Research	B-Operating_System
Unix	I-Operating_System
and	O
System	B-Operating_System
V	I-Operating_System
.	O
With	O
the	O
addition	O
of	O
virtual	B-Architecture
memory	I-Architecture
support	O
to	O
3BSD	O
,	O
this	O
got	O
renamed	O
/vmunix./usrThe	O
"	O
user	O
file	B-Application
system	I-Application
"	O
:	O
originally	O
the	O
directory	B-Application
holding	O
user	O
home	B-Application
directories	I-Application
,	O
but	O
already	O
by	O
the	O
Third	B-Operating_System
Edition	I-Operating_System
of	O
Research	B-Operating_System
Unix	I-Operating_System
,	O
ca	O
.	O
</s>
<s>
1973	O
,	O
reused	O
to	O
split	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
programs	O
over	O
two	O
disks	O
(	O
one	O
of	O
them	O
a	O
256K	O
fixed-head	O
drive	O
)	O
so	O
that	O
basic	O
commands	O
would	O
either	O
appear	O
in	O
/bin	O
or	O
/usr/bin.M.	O
</s>
<s>
A	O
Research	B-Operating_System
Unix	I-Operating_System
reader	O
:	O
annotated	O
excerpts	O
from	O
the	O
Programmer	O
's	O
Manual	O
,	O
1971	O
–	O
1986	O
.	O
</s>
<s>
It	O
now	O
holds	O
executables	O
,	O
libraries	O
,	O
and	O
shared	B-General_Concept
resources	I-General_Concept
that	O
are	O
not	O
system	O
critical	O
,	O
such	O
as	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
,	O
window	B-Application
managers	I-Application
,	O
scripting	B-Language
languages	I-Language
,	O
etc	O
.	O
</s>
<s>
In	O
older	O
Unix	B-Application
systems	I-Application
,	O
user	O
home	B-Application
directories	I-Application
might	O
still	O
appear	O
in	O
/usr	O
alongside	O
directories	B-Application
containing	O
programs	O
,	O
although	O
by	O
1984	O
this	O
depended	O
on	O
local	O
customs./includeStores	O
the	O
development	O
headers	O
used	O
throughout	O
the	O
system	O
.	O
</s>
<s>
Header	B-Language
files	I-Language
are	O
mostly	O
used	O
by	O
the	O
#include	O
directive	O
in	O
C	B-Language
language	I-Language
,	O
which	O
historically	O
is	O
how	O
the	O
name	O
of	O
this	O
directory	B-Application
was	O
chosen./libStores	O
the	O
needed	O
libraries	O
and	O
data	O
files	O
for	O
programs	O
stored	O
within	O
/usr	O
or	O
elsewhere./libexecHolds	O
programs	O
meant	O
to	O
be	O
executed	O
by	O
other	O
programs	O
rather	O
than	O
by	O
users	O
directly	O
.	O
</s>
<s>
E.g.	O
,	O
the	O
Sendmail	B-Application
executable	O
may	O
be	O
found	O
in	O
this	O
directory	B-Application
.	O
</s>
<s>
Not	O
present	O
in	O
the	O
FHS	O
until	O
2011	O
;	O
Linux	B-Application
distributions	I-Application
have	O
traditionally	O
moved	O
the	O
contents	O
of	O
this	O
directory	B-Application
into	O
/usr/lib	O
,	O
where	O
they	O
also	O
resided	O
in	O
4.3BSD./localResembles	O
/usr	O
in	O
structure	O
,	O
but	O
its	O
subdirectories	B-Application
are	O
used	O
for	O
additions	O
not	O
part	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
distribution	O
,	O
such	O
as	O
custom	O
programs	O
or	O
files	O
from	O
a	O
BSD	B-Application
Ports	I-Application
collection	O
.	O
</s>
<s>
Usually	O
has	O
subdirectories	B-Application
such	O
as	O
/usr/local/lib	O
or	O
/usr/local/bin./shareArchitecture	O
-independent	O
program	O
data	O
.	O
</s>
<s>
On	O
Linux	O
and	O
modern	O
BSD	B-Operating_System
derivatives	O
,	O
this	O
directory	B-Application
has	O
subdirectories	B-Application
such	O
as	O
man	O
for	O
manpages	B-Protocol
,	O
that	O
used	O
to	O
appear	O
directly	O
under	O
/usr	O
in	O
older	O
versions./varStands	O
for	O
variable	O
.	O
</s>
<s>
Often	O
,	O
this	O
directory	B-Application
is	O
a	O
symbolic	B-Application
link	I-Application
to	O
/var/spool/mail./spoolSpool	O
directory	B-Application
.	O
</s>
<s>
Contains	O
print	O
jobs	O
,	O
mail	O
spools	B-Device
and	O
other	O
queued	O
tasks./srcThe	O
place	O
where	O
the	O
uncompiled	O
source	O
code	O
of	O
some	O
programs	O
is./tmpThe	O
/var/tmp	O
directory	B-Application
is	O
a	O
place	O
for	O
temporary	O
files	O
which	O
should	O
be	O
preserved	O
between	O
system	O
reboots	O
.	O
</s>
