<s>
The	O
proc	B-Application
filesystem	I-Application
(	O
procfs	B-Application
)	O
is	O
a	O
special	O
filesystem	O
in	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
that	O
presents	O
information	O
about	O
processes	O
and	O
other	O
system	O
information	O
in	O
a	O
hierarchical	O
file-like	O
structure	O
,	O
providing	O
a	O
more	O
convenient	O
and	O
standardized	O
method	O
for	O
dynamically	O
accessing	O
process	B-Operating_System
data	O
held	O
in	O
the	O
kernel	B-Operating_System
than	O
traditional	O
tracing	O
methods	O
or	O
direct	O
access	O
to	O
kernel	B-Operating_System
memory	O
.	O
</s>
<s>
Typically	O
,	O
it	O
is	O
mapped	B-General_Concept
to	O
a	O
mount	O
point	O
named	O
/proc	B-Application
at	O
boot	O
time	O
.	O
</s>
<s>
The	O
proc	B-Application
file	I-Application
system	I-Application
acts	O
as	O
an	O
interface	O
to	O
internal	O
data	O
structures	O
about	O
running	O
processes	O
in	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
In	O
Linux	B-Operating_System
,	O
it	O
can	O
also	O
be	O
used	O
to	O
obtain	O
information	O
about	O
the	O
kernel	B-Operating_System
and	O
to	O
change	O
certain	O
kernel	B-Operating_System
parameters	O
at	O
runtime	O
(	O
sysctl	B-Application
)	O
.	O
</s>
<s>
Many	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
support	O
the	O
proc	B-Application
filesystem	I-Application
,	O
including	O
Solaris	B-Application
,	O
IRIX	B-Operating_System
,	O
Tru64	B-Operating_System
UNIX	I-Operating_System
,	O
BSD	B-Operating_System
,	O
Linux	B-Operating_System
,	O
IBM	B-Application
AIX	I-Application
,	O
QNX	B-Operating_System
,	O
and	O
Plan	B-Operating_System
9	I-Operating_System
from	I-Operating_System
Bell	I-Operating_System
Labs	I-Operating_System
.	O
</s>
<s>
OpenBSD	B-Operating_System
dropped	O
support	O
in	O
version	O
5.7	O
,	O
released	O
in	O
May	O
2015	O
.	O
</s>
<s>
It	O
is	O
absent	O
from	O
HP-UX	B-Application
and	O
macOS	B-Application
.	O
</s>
<s>
The	O
Linux	B-Operating_System
kernel	I-Operating_System
extends	O
it	O
to	O
non	O
–	O
process-related	O
data	O
.	O
</s>
<s>
The	O
proc	B-Application
filesystem	I-Application
provides	O
a	O
method	O
of	O
communication	O
between	O
kernel	B-Operating_System
space	I-Operating_System
and	O
user	B-Operating_System
space	I-Operating_System
.	O
</s>
<s>
For	O
example	O
,	O
the	O
GNU	B-Operating_System
version	O
of	O
the	O
process	B-Operating_System
reporting	O
utility	O
ps	B-Application
uses	O
the	O
proc	B-Application
file	I-Application
system	I-Application
to	O
obtain	O
its	O
data	O
,	O
without	O
using	O
any	O
specialized	O
system	B-Operating_System
calls	I-Operating_System
.	O
</s>
<s>
Tom	O
J	O
.	O
Killian	O
implemented	O
the	O
UNIX	B-Operating_System
8th	I-Operating_System
Edition	I-Operating_System
(	O
V8	O
)	O
version	O
of	O
/proc	B-Application
:	O
he	O
presented	O
a	O
paper	O
titled	O
at	O
USENIX	B-Operating_System
in	O
June	O
1984	O
.	O
</s>
<s>
The	O
design	O
of	O
procfs	B-Application
aimed	O
to	O
replace	O
the	O
ptrace	B-Operating_System
system	B-Operating_System
call	I-Operating_System
used	O
for	O
process	B-Operating_System
tracing	O
.	O
</s>
<s>
Roger	O
Faulkner	O
and	O
Ron	O
Gomes	O
ported	O
V8	O
/proc	B-Application
to	O
SVR4	O
,	O
and	O
published	O
a	O
paper	O
called	O
at	O
USENIX	B-Operating_System
in	O
January	O
1991	O
.	O
</s>
<s>
This	O
kind	O
of	O
procfs	B-Application
supported	O
the	O
creation	O
of	O
ps	B-Application
,	O
but	O
the	O
files	O
could	O
only	O
be	O
accessed	O
with	O
functions	O
read( )	O
,	O
write( )	O
,	O
and	O
ioctl( )	O
.	O
</s>
<s>
Between	O
1995	O
and	O
1996	O
,	O
Roger	O
Faulkner	O
created	O
the	O
procfs-2	O
interface	O
for	O
Solaris-2.6	O
that	O
offers	O
a	O
structured	O
/proc	B-Application
filesystem	O
with	O
sub-directories	O
.	O
</s>
<s>
Plan	B-Operating_System
9	I-Operating_System
implemented	O
a	O
process	B-Operating_System
file	O
system	O
,	O
but	O
went	O
further	O
than	O
V8	O
.	O
</s>
<s>
V8	O
's	O
process	B-Operating_System
file	O
system	O
implemented	O
a	O
single	O
file	O
per	O
process	B-Operating_System
.	O
</s>
<s>
Plan	B-Operating_System
9	I-Operating_System
created	O
a	O
hierarchy	O
of	O
separate	O
files	O
to	O
provide	O
those	O
functions	O
,	O
and	O
made	O
/proc	B-Application
a	O
real	O
part	O
of	O
the	O
file	O
system	O
.	O
</s>
<s>
,	O
procfs	B-Application
is	O
gradually	O
becoming	O
phased	O
out	O
in	O
FreeBSD	O
,	O
and	O
turned	O
to	O
use	O
the	O
sysctl	B-Application
instead	O
for	O
process-related	O
information	O
.	O
</s>
<s>
It	O
was	O
removed	O
from	O
OpenBSD	B-Operating_System
in	O
version	O
5.7	O
,	O
which	O
was	O
released	O
in	O
May	O
2015	O
,	O
because	O
it	O
"	O
always	O
suffered	O
from	O
race	O
conditions	O
and	O
is	O
now	O
unused	O
"	O
.	O
</s>
<s>
macOS	B-Application
did	O
n't	O
implement	O
procfs	B-Application
and	O
user	B-Operating_System
space	I-Operating_System
programs	O
have	O
to	O
use	O
sysctl	B-Application
interface	O
for	O
processes	O
data	O
.	O
</s>
<s>
To	O
provide	O
binary	O
compatibility	O
with	O
Linux	B-Operating_System
user	B-Operating_System
space	I-Operating_System
programs	O
,	O
FreeBSD	O
kernel	B-Operating_System
also	O
provides	O
linprocfs	O
that	O
is	O
similar	O
to	O
the	O
Linux	B-Operating_System
procfs	B-Application
.	O
</s>
<s>
/proc	B-Application
in	O
Solaris	B-Application
was	O
available	O
from	O
the	O
beginning	O
.	O
</s>
<s>
Solaris	B-Application
2.6	O
in	O
1996	O
introduced	O
procfs2	O
from	O
Roger	O
Faulkner	O
.	O
</s>
<s>
Linux	B-Operating_System
first	O
added	O
a	O
/proc	B-Application
filesystem	O
in	O
,	O
September	O
1992	O
,	O
and	O
first	O
began	O
expanding	O
it	O
to	O
non-process	O
related	O
data	O
in	O
v0.98.6	O
,	O
December	O
1992	O
.	O
</s>
<s>
As	O
of	O
2020	O
,	O
the	O
Linux	B-Operating_System
implementation	O
includes	O
a	O
directory	O
for	O
each	O
running	O
process	B-Operating_System
,	O
including	O
kernel	B-Operating_System
processes	O
,	O
in	O
directories	O
named	O
,	O
where	O
is	O
the	O
process	B-Operating_System
number	O
.	O
</s>
<s>
Each	O
directory	O
contains	O
information	O
about	O
one	O
process	B-Operating_System
,	O
including	O
:	O
</s>
<s>
,	O
the	O
command	O
that	O
originally	O
started	O
the	O
process	B-Operating_System
.	O
</s>
<s>
,	O
a	O
symlink	B-Application
to	O
the	O
current	B-Application
working	I-Application
directory	I-Application
of	O
the	O
process	B-Operating_System
.	O
</s>
<s>
contains	O
the	O
names	O
and	O
values	O
of	O
the	O
environment	O
variables	O
that	O
affect	O
the	O
process	B-Operating_System
.	O
</s>
<s>
,	O
a	O
symlink	B-Application
to	O
the	O
original	O
executable	B-Application
file	I-Application
,	O
if	O
it	O
still	O
exists	O
(	O
a	O
process	B-Operating_System
may	O
continue	O
running	O
after	O
its	O
original	O
executable	B-Application
has	O
been	O
deleted	O
or	O
replaced	O
)	O
.	O
</s>
<s>
,	O
a	O
directory	O
containing	O
a	O
symbolic	B-Application
link	I-Application
for	O
each	O
open	O
file	B-Application
descriptor	I-Application
.	O
</s>
<s>
,	O
a	O
directory	O
containing	O
entries	O
which	O
describe	O
the	O
position	O
and	O
flags	O
for	O
each	O
open	O
file	B-Application
descriptor	I-Application
.	O
</s>
<s>
,	O
a	O
text	O
file	O
containing	O
information	O
about	O
mapped	B-General_Concept
files	O
and	O
blocks	O
(	O
like	O
heap	O
and	O
stack	O
)	O
.	O
</s>
<s>
,	O
a	O
binary	O
image	O
representing	O
the	O
process	B-Operating_System
's	O
virtual	B-Architecture
memory	I-Architecture
,	O
can	O
only	O
be	O
accessed	O
by	O
a	O
ptrace'ing	O
process	B-Operating_System
.	O
</s>
<s>
,	O
a	O
symlink	B-Application
to	O
the	O
root	O
path	O
as	O
seen	O
by	O
the	O
process	B-Operating_System
.	O
</s>
<s>
For	O
most	O
processes	O
this	O
will	O
be	O
a	O
link	O
to	O
/	O
unless	O
the	O
process	B-Operating_System
is	O
running	O
in	O
a	O
chroot	B-Application
jail	I-Application
.	O
</s>
<s>
contains	O
basic	O
information	O
about	O
a	O
process	B-Operating_System
including	O
its	O
run	O
state	O
and	O
memory	O
usage	O
.	O
</s>
<s>
,	O
a	O
directory	O
containing	O
hard	B-Application
links	I-Application
to	O
any	O
tasks	O
that	O
have	O
been	O
started	O
by	O
this	O
(	O
i.e.	O
</s>
<s>
:	O
the	O
parent	O
)	O
process	B-Operating_System
.	O
</s>
<s>
(	O
Users	O
may	O
obtain	O
the	O
PID	B-Operating_System
with	O
a	O
utility	O
such	O
as	O
pgrep	B-Device
,	O
pidof	O
or	O
ps	B-Application
:	O
</s>
<s>
also	O
includes	O
non-process-related	O
system	O
information	O
,	O
although	O
in	O
the	O
2.6	O
kernel	B-Operating_System
much	O
of	O
that	O
information	O
moved	O
to	O
a	O
separate	O
pseudo-file	O
system	O
,	O
sysfs	B-Application
,	O
mounted	O
under	O
:	O
</s>
<s>
depending	O
on	O
the	O
mode	O
of	O
power	O
management	O
(	O
if	O
at	O
all	O
)	O
,	O
either	O
directory	O
,	O
or	O
,	O
which	O
predate	O
sysfs	B-Application
and	O
contain	O
various	O
bits	O
of	O
information	O
about	O
the	O
state	O
of	O
power	O
management	O
.	O
</s>
<s>
,	O
information	O
about	O
the	O
buddy	B-General_Concept
algorithm	I-General_Concept
that	O
handles	O
memory	O
fragmentation	O
.	O
</s>
<s>
,	O
containing	O
directories	O
representing	O
various	O
buses	O
on	O
the	O
computer	O
,	O
such	O
as	O
PCI/USB	O
.	O
</s>
<s>
This	O
has	O
been	O
largely	O
superseded	O
by	O
sysfs	B-Application
under	O
/sys/bus	O
which	O
is	O
far	O
more	O
informative	O
.	O
</s>
<s>
,	O
containing	O
information	O
about	O
the	O
CPU	B-General_Concept
,	O
such	O
as	O
its	O
vendor	O
(	O
and	O
CPU	B-General_Concept
family	O
,	O
model	O
and	O
model	O
names	O
which	O
should	O
allow	O
users	O
to	O
identify	O
the	O
CPU	B-General_Concept
)	O
and	O
its	O
speed	O
(	O
CPU	B-General_Concept
clockspeed	O
)	O
,	O
cache	O
size	O
,	O
number	O
of	O
siblings	O
,	O
cores	O
,	O
and	O
CPU	B-General_Concept
flags	O
.	O
</s>
<s>
On	O
some	O
architectures	O
,	O
includes	O
a	O
value	O
for	O
"	O
bogomips	B-Application
"	O
,	O
frequently	O
misconstrued	O
as	O
a	O
measure	O
of	O
CPU	B-General_Concept
speed	O
,	O
like	O
a	O
benchmark	O
,	O
but	O
it	O
does	O
not	O
actually	O
measure	O
any	O
sensible	O
(	O
for	O
end-users	O
)	O
value	O
at	O
all	O
.	O
</s>
<s>
It	O
occurs	O
as	O
a	O
side-effect	O
of	O
kernel	B-Operating_System
timer	O
calibration	O
and	O
yields	O
highly	O
varying	O
values	O
depending	O
on	O
CPU	B-General_Concept
type	O
,	O
even	O
at	O
equal	O
clock	O
speeds	O
.	O
</s>
<s>
On	O
multi-core	O
CPUs	O
,	O
/proc/cpuinfo	B-Application
contains	O
the	O
fields	O
for	O
"	O
siblings	O
"	O
and	O
"	O
cpu	B-General_Concept
cores	O
"	O
which	O
represent	O
the	O
following	O
calculation	O
is	O
applied	O
:	O
</s>
<s>
A	O
CPU	B-General_Concept
package	O
means	O
physical	O
CPU	B-General_Concept
which	O
can	O
have	O
multiple	O
cores	O
(	O
single	O
core	O
for	O
one	O
,	O
dual	O
core	O
for	O
two	O
,	O
quad	O
core	O
for	O
four	O
)	O
.	O
</s>
<s>
This	O
allows	O
a	O
distinction	O
between	O
hyper-threading	B-Operating_System
and	O
dual-core	O
,	O
i.e.	O
</s>
<s>
the	O
number	O
of	O
hyper-threads	O
per	O
CPU	B-General_Concept
package	O
can	O
be	O
calculated	O
by	O
siblings	O
/	O
CPU	B-General_Concept
cores	O
.	O
</s>
<s>
If	O
both	O
values	O
for	O
a	O
CPU	B-General_Concept
package	O
are	O
the	O
same	O
,	O
then	O
hyper-threading	B-Operating_System
is	O
not	O
supported	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
CPU	B-General_Concept
package	O
with	O
siblings	O
=	O
2	O
and	O
"	O
cpu	B-General_Concept
cores	O
"	O
=	O
2	O
is	O
a	O
dual-core	O
CPU	B-General_Concept
but	O
does	O
not	O
support	O
hyper-threading	B-Operating_System
.	O
</s>
<s>
,	O
containing	O
a	O
summary	O
of	O
how	O
the	O
kernel	B-Operating_System
is	O
managing	O
its	O
memory	O
.	O
</s>
<s>
,	O
one	O
of	O
the	O
most	O
important	O
files	O
in	O
,	O
containing	O
a	O
list	O
of	O
the	O
kernel	B-Operating_System
modules	O
currently	O
loaded	O
.	O
</s>
<s>
,	O
a	O
symlink	B-Application
to	O
self/mounts	O
which	O
contains	O
a	O
list	O
of	O
the	O
currently	O
mounted	O
devices	O
and	O
their	O
mount	O
points	O
(	O
and	O
which	O
file	O
system	O
is	O
in	O
use	O
and	O
what	O
mount	O
options	O
are	O
in	O
use	O
)	O
.	O
</s>
<s>
a	O
symbolic	B-Application
link	I-Application
to	O
the	O
current	O
(	O
traversing	O
)	O
process	B-Operating_System
at	O
(	O
i.e.	O
</s>
<s>
where	O
PID	B-Operating_System
is	O
that	O
of	O
the	O
current	O
process	B-Operating_System
)	O
.	O
</s>
<s>
Access	O
to	O
dynamically	O
configurable	O
kernel	B-Operating_System
options	O
under	O
.	O
</s>
<s>
Under	O
appear	O
directories	O
representing	O
the	O
areas	O
of	O
kernel	B-Operating_System
,	O
containing	O
readable	O
and	O
writable	O
virtual	O
files	O
.	O
</s>
<s>
,	O
containing	O
memory-sharing	O
and	O
inter-process	B-Operating_System
communication	I-Operating_System
(	O
IPC	O
)	O
information	O
.	O
</s>
<s>
other	O
files	O
depending	O
on	O
various	O
hardware	O
,	O
module	O
configurations	O
,	O
and	O
changes	O
to	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
The	O
basic	O
utilities	O
that	O
use	O
/proc	B-Application
under	O
Linux	B-Operating_System
come	O
in	O
the	O
procps	O
(	O
processes	O
)	O
package	O
,	O
and	O
only	O
function	O
in	O
conjunction	O
with	O
a	O
mounted	O
.	O
</s>
<s>
Cygwin	B-Language
implemented	O
a	O
procfs	B-Application
that	O
is	O
basically	O
the	O
same	O
as	O
the	O
Linux	B-Operating_System
procfs	B-Application
.	O
</s>
