<s>
Everything	B-Application
is	I-Application
a	I-Application
file	I-Application
is	O
an	O
idea	O
that	O
Unix	B-Application
,	O
and	O
its	O
derivatives	O
,	O
handle	O
input/output	B-General_Concept
to	O
and	O
from	O
resources	B-General_Concept
such	O
as	O
documents	O
,	O
hard-drives	O
,	O
modems	O
,	O
keyboards	O
,	O
printers	O
and	O
even	O
some	O
inter-process	O
and	O
network	O
communications	O
as	O
simple	O
streams	B-Architecture
of	O
bytes	O
exposed	O
through	O
the	O
filesystem	O
name	O
space	O
.	O
</s>
<s>
Exceptions	O
include	O
shared	O
memory	O
,	O
semaphores	O
,	O
datagram	O
sockets	O
,	O
symbolic	B-Application
links	I-Application
,	O
directories	B-Application
(	O
which	O
are	O
read-only	O
,	O
and	O
are	O
not	O
accessed	O
as	O
a	O
byte-stream	O
)	O
,	O
processes	O
and	O
threads	B-Operating_System
.	O
</s>
<s>
The	O
advantage	O
of	O
this	O
approach	O
is	O
that	O
the	O
same	O
set	O
of	O
tools	O
,	O
utilities	O
and	O
APIs	B-General_Concept
can	O
be	O
used	O
on	O
a	O
wide	O
range	O
of	O
resources	B-General_Concept
and	O
a	O
number	O
of	O
file	B-Application
types	I-Application
.	O
</s>
<s>
When	O
a	O
file	O
is	O
opened	O
,	O
a	O
file	B-Application
descriptor	I-Application
is	O
created	O
,	O
using	O
the	O
file	B-Application
path	I-Application
as	O
an	O
addressing	O
system	O
.	O
</s>
<s>
The	O
file	B-Application
descriptor	I-Application
is	O
then	O
a	O
byte	O
stream	O
I/O	B-General_Concept
interface	I-General_Concept
on	O
which	O
file	O
operations	O
are	O
performed	O
.	O
</s>
<s>
Additionally	O
,	O
file	B-Application
descriptors	I-Application
are	O
also	O
created	O
for	O
objects	O
such	O
as	O
anonymous	B-Operating_System
pipes	I-Operating_System
and	O
network	B-Protocol
sockets	I-Protocol
-	O
and	O
therefore	O
a	O
more	O
accurate	O
description	O
of	O
this	O
feature	O
is	O
Everything	B-Application
is	I-Application
a	I-Application
file	I-Application
descriptor	O
.	O
</s>
<s>
These	O
are	O
mounted	B-Application
into	O
the	O
single	O
file	O
hierarchy	O
.	O
</s>
<s>
An	O
example	O
of	O
this	O
purely	O
virtual	O
filesystem	O
is	O
under	O
/proc	B-Application
that	O
exposes	O
many	O
system	O
properties	O
as	O
files	O
.	O
</s>
<s>
All	O
of	O
these	O
files	O
,	O
in	O
the	O
broader	O
sense	O
of	O
the	O
word	O
,	O
have	O
standard	O
Unix	B-Application
file	O
attributes	O
such	O
as	O
an	B-Device
owner	I-Device
and	O
access	B-Application
permissions	I-Application
,	O
and	O
can	O
be	O
queried	O
by	O
the	O
same	O
classic	B-Application
Unix	I-Application
tools	I-Application
and	O
filters	O
.	O
</s>
<s>
Some	O
operating	O
systems	O
do	O
not	O
even	O
mount	O
/proc	B-Application
by	O
default	O
due	O
to	O
security	O
or	O
speed	O
concerns	O
.	O
</s>
<s>
It	O
is	O
,	O
though	O
,	O
used	O
heavily	O
by	O
both	O
the	O
widely	O
installed	O
BusyBox	B-Application
on	O
embedded	B-Architecture
systems	I-Architecture
and	O
by	O
procps	O
,	O
which	O
is	O
used	O
on	O
most	O
Linux	B-Application
systems	O
.	O
</s>
<s>
It	O
is	O
similarly	O
used	O
on	O
Android	B-Application
systems	I-Application
in	O
the	O
operating	O
system	O
's	O
Toolbox	O
program	O
.	O
</s>
