<s>
GNU	B-Application
Hurd	I-Application
is	O
a	O
collection	O
of	O
microkernel	B-Operating_System
servers	O
written	O
as	O
part	O
of	O
GNU	B-Operating_System
,	O
for	O
the	O
GNU	B-Operating_System
Mach	I-Operating_System
microkernel	B-Operating_System
.	O
</s>
<s>
It	O
has	O
been	O
under	O
development	O
since	O
1990	O
by	O
the	B-Application
GNU	I-Application
Project	I-Application
of	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
,	O
designed	O
as	O
a	O
replacement	O
for	O
the	O
Unix	B-Application
kernel	B-Operating_System
,	O
and	O
released	O
as	O
free	B-Application
software	I-Application
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
When	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
proved	O
to	O
be	O
a	O
viable	O
solution	O
,	O
development	O
of	O
GNU	B-Application
Hurd	I-Application
slowed	O
,	O
at	O
times	O
alternating	O
between	O
stasis	O
and	O
renewed	O
activity	O
and	O
interest	O
.	O
</s>
<s>
The	B-Application
Hurd	I-Application
's	O
design	O
consists	O
of	O
a	O
set	O
of	O
protocols	O
and	O
server	B-Application
processes	I-Application
(	O
or	O
daemons	B-Operating_System
,	O
in	O
Unix	B-Application
terminology	O
)	O
that	O
run	O
on	O
the	O
GNU	B-Operating_System
Mach	I-Operating_System
microkernel	B-Operating_System
.	O
</s>
<s>
The	B-Application
Hurd	I-Application
aims	O
to	O
surpass	O
the	O
Unix	B-Application
kernel	B-Operating_System
in	O
functionality	O
,	O
security	O
,	O
and	O
stability	O
,	O
while	O
remaining	O
largely	O
compatible	O
with	O
it	O
.	O
</s>
<s>
The	B-Application
GNU	I-Application
Project	I-Application
chose	O
the	O
multiserver	O
microkernel	B-Operating_System
for	O
the	O
operating	O
system	O
,	O
due	O
to	O
perceived	O
advantages	O
over	O
the	O
traditional	B-Application
Unix	I-Application
monolithic	B-Operating_System
kernel	I-Operating_System
architecture	O
,	O
a	O
view	O
that	O
had	O
been	O
advocated	O
by	O
some	O
developers	O
in	O
the	O
1980s	O
.	O
</s>
<s>
In	O
December	O
1991	O
the	O
primary	O
architect	O
of	O
the	B-Application
Hurd	I-Application
described	O
the	O
name	O
as	O
a	O
mutually	B-Algorithm
recursive	I-Algorithm
acronym	O
:	O
</s>
<s>
As	O
both	O
hurd	B-Application
and	O
hird	O
are	O
homophones	O
of	O
the	O
English	O
word	O
herd	O
,	O
the	O
full	O
name	O
GNU	B-Application
Hurd	I-Application
is	O
also	O
a	O
play	O
on	O
the	O
words	O
herd	O
of	O
gnus	B-Operating_System
,	O
reflecting	O
how	O
the	O
kernel	B-Operating_System
works	O
.	O
</s>
<s>
The	O
logo	O
is	O
called	O
the	B-Application
Hurd	I-Application
boxes	O
and	O
it	O
also	O
reflects	O
on	O
architecture	O
.	O
</s>
<s>
The	O
logo	O
is	O
a	O
graph	O
where	O
nodes	O
represent	O
the	B-Application
Hurd	I-Application
kernel	B-Operating_System
's	O
servers	O
and	O
directed	O
edges	O
are	O
IPC	B-Operating_System
messages	O
.	O
</s>
<s>
Richard	O
Stallman	O
founded	O
the	B-Application
GNU	I-Application
Project	I-Application
in	O
September	O
1983	O
with	O
an	O
aim	O
to	O
create	O
a	O
free	B-Application
GNU	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
.	O
</s>
<s>
Initially	O
the	O
components	O
required	O
for	O
kernel	B-Operating_System
development	O
were	O
written	O
:	O
editors	B-Application
,	O
shell	B-Application
,	O
compiler	B-Language
,	O
debugger	B-Application
etc	O
.	O
</s>
<s>
By	O
1989	O
,	O
the	O
GNU	B-License
GPL	I-License
came	O
into	O
being	O
and	O
the	O
only	O
major	O
component	O
missing	O
was	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
Development	O
on	O
the	B-Application
Hurd	I-Application
began	O
in	O
1990	O
after	O
an	O
abandoned	O
kernel	B-Operating_System
attempt	O
in	O
1986	O
,	O
based	O
on	O
the	O
research	O
TRIX	B-Application
operating	O
system	O
developed	O
by	O
Professor	O
Steve	O
Ward	O
and	O
his	O
group	O
at	O
MIT	O
's	O
Laboratory	O
for	O
Computer	O
Science	O
(	O
LCS	O
)	O
.	O
</s>
<s>
According	O
to	O
Thomas	O
Bushnell	O
,	O
the	O
initial	O
Hurd	B-Application
architect	O
,	O
their	O
early	O
plan	O
was	O
to	O
adapt	O
the	O
4.4BSD-Lite	O
kernel	B-Operating_System
and	O
,	O
in	O
hindsight	O
,	O
"	O
It	O
is	O
now	O
perfectly	O
obvious	O
to	O
me	O
that	O
this	O
would	O
have	O
succeeded	O
splendidly	O
and	O
the	O
world	O
would	O
be	O
a	O
very	O
different	O
place	O
today.	O
"	O
</s>
<s>
In	O
1987	O
Richard	O
Stallman	O
proposed	O
using	O
the	O
Mach	B-Operating_System
microkernel	I-Operating_System
developed	O
by	O
Richard	O
Rashid	O
at	O
Carnegie	O
Mellon	O
University	O
.	O
</s>
<s>
Work	O
on	O
this	O
was	O
delayed	O
for	O
three	O
years	O
due	O
to	O
uncertainty	O
over	O
whether	O
CMU	O
would	O
release	O
the	O
Mach	B-Operating_System
code	O
under	O
a	O
suitable	O
license	O
.	O
</s>
<s>
With	O
the	O
release	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
in	O
1991	O
,	O
the	O
primary	O
user	O
of	O
GNU	B-Operating_System
's	O
userland	O
components	O
soon	O
became	O
operating	O
systems	O
based	O
on	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
(	O
Linux	B-Application
distributions	I-Application
)	O
,	O
prompting	O
the	O
coining	O
of	O
the	O
term	O
GNU/Linux	B-Application
.	O
</s>
<s>
Development	O
of	O
the	B-Application
Hurd	I-Application
has	O
proceeded	O
slowly	O
.	O
</s>
<s>
Despite	O
an	O
optimistic	O
announcement	O
by	O
Stallman	O
in	O
2002	O
predicting	O
a	O
release	O
of	O
GNU/Hurd	B-Application
later	O
that	O
year	O
,	O
the	B-Application
Hurd	I-Application
is	O
still	O
not	O
considered	O
suitable	O
for	O
production	O
environments	O
.	O
</s>
<s>
In	O
2010	O
,	O
after	O
twenty	O
years	O
under	O
development	O
,	O
Stallman	O
said	O
that	O
he	O
was	O
"	O
not	O
very	O
optimistic	O
about	O
the	O
GNU	B-Application
Hurd	I-Application
.	O
</s>
<s>
It	O
makes	O
some	O
progress	O
,	O
but	O
to	O
be	O
really	O
superior	O
it	O
would	O
require	O
solving	O
a	O
lot	O
of	O
deep	O
problems	O
"	O
,	O
but	O
added	O
that	O
"	O
finishing	O
it	O
is	O
not	O
crucial	O
"	O
for	O
the	B-Operating_System
GNU	I-Operating_System
system	I-Operating_System
because	O
a	O
free	B-Application
kernel	B-Operating_System
already	O
existed	O
(	O
Linux	B-Operating_System
)	O
,	O
and	O
completing	O
Hurd	B-Application
would	O
not	O
address	O
the	O
main	O
remaining	O
problem	O
for	O
a	O
free	B-Application
operating	O
system	O
:	O
device	O
support	O
.	O
</s>
<s>
The	O
Debian	O
project	O
,	O
among	O
others	O
,	O
have	O
worked	O
on	O
the	B-Application
Hurd	I-Application
project	O
to	O
produce	O
binary	O
distributions	O
of	O
Hurd-based	O
GNU	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
for	O
IBM	O
PC	O
compatible	O
systems	O
.	O
</s>
<s>
On	O
August	O
20	O
,	O
2015	O
,	O
amid	O
the	O
Google	B-Application
Summer	I-Application
of	I-Application
Code	I-Application
,	O
it	O
was	O
announced	O
that	O
GNU	B-Application
Guix	I-Application
had	O
been	O
ported	O
to	O
GNU	B-Application
Hurd	I-Application
.	O
</s>
<s>
Unlike	O
most	O
Unix-like	B-Operating_System
kernels	B-Operating_System
,	O
the	B-Application
Hurd	I-Application
uses	O
a	O
server	B-Operating_System
–	I-Operating_System
client	I-Operating_System
architecture	I-Operating_System
,	O
built	O
on	O
a	O
microkernel	B-Operating_System
that	O
is	O
responsible	O
for	O
providing	O
the	O
most	O
basic	O
kernel	B-Operating_System
services	O
–	O
coordinating	O
access	O
to	O
the	O
hardware	B-Architecture
:	O
the	O
CPU	B-General_Concept
(	O
through	O
process	B-Operating_System
management	I-Operating_System
and	O
scheduling	O
)	O
,	O
RAM	B-Architecture
(	O
via	O
memory	B-General_Concept
management	I-General_Concept
)	O
,	O
and	O
other	O
various	O
input/output	B-General_Concept
devices	I-General_Concept
(	O
via	O
I/O	B-General_Concept
scheduling	I-General_Concept
)	O
for	O
sound	O
,	O
graphics	O
,	O
mass	O
storage	O
,	O
etc	O
.	O
</s>
<s>
In	O
theory	O
,	O
the	O
microkernel	B-Operating_System
design	O
would	O
allow	O
for	O
all	O
device	O
drivers	O
to	O
be	O
built	O
as	O
servers	O
working	O
in	O
user	B-Operating_System
space	I-Operating_System
,	O
but	O
today	O
most	O
drivers	O
of	O
this	O
kind	O
are	O
still	O
contained	O
in	O
the	O
GNU	B-Operating_System
Mach	I-Operating_System
kernel	B-Operating_System
space	I-Operating_System
.	O
</s>
<s>
According	O
to	O
Hurd	B-Application
developers	O
,	O
the	O
main	O
advantage	O
of	O
microkernel-based	O
design	O
is	O
the	O
ability	O
to	O
extend	O
the	O
system	O
:	O
developing	O
a	O
new	O
module	O
would	O
not	O
require	O
in	O
depth	O
knowledge	O
of	O
the	O
rest	O
of	O
the	O
kernel	B-Operating_System
,	O
and	O
a	O
bug	O
in	O
one	O
module	O
would	O
not	O
crash	B-General_Concept
the	O
entire	O
system	O
.	O
</s>
<s>
Hurd	B-Application
provides	O
a	O
concept	O
of	O
translators	O
,	O
a	O
framework	O
of	O
modules	O
used	O
to	O
extend	O
a	O
file	B-Application
system	I-Application
functionality	O
.	O
</s>
<s>
From	O
early	O
on	O
,	O
the	B-Application
Hurd	I-Application
was	O
developed	O
to	O
use	O
GNU	B-Operating_System
Mach	I-Operating_System
as	O
the	O
microkernel	B-Operating_System
.	O
</s>
<s>
Other	O
Unix-like	B-Operating_System
systems	I-Operating_System
working	O
on	O
the	O
Mach	B-Operating_System
microkernel	I-Operating_System
include	O
OSF/1	B-Operating_System
,	O
Lites	B-Operating_System
,	O
and	O
MkLinux	B-Application
.	O
</s>
<s>
macOS	B-Application
and	O
NeXTSTEP	B-Application
use	O
hybrid	B-Operating_System
kernels	I-Operating_System
based	O
on	O
Mach	B-Operating_System
.	O
</s>
<s>
From	O
2004	O
onward	O
,	O
various	O
efforts	O
were	O
launched	O
to	O
port	O
the	B-Application
Hurd	I-Application
to	O
more	O
modern	O
microkernels	B-Operating_System
.	O
</s>
<s>
The	O
L4	B-Operating_System
microkernel	I-Operating_System
was	O
the	O
original	O
choice	O
in	O
2004	O
,	O
but	O
progress	O
slowed	O
to	O
a	O
halt	O
.	O
</s>
<s>
Nevertheless	O
,	O
during	O
2005	O
,	O
Hurd	B-Application
developer	O
Neal	O
Walfield	O
finished	O
the	O
initial	O
memory	B-General_Concept
management	I-General_Concept
framework	O
for	O
the	O
L4/Hurd	O
port	O
,	O
and	O
Marcus	O
Brinkmann	O
ported	O
essential	O
parts	O
of	O
glibc	B-Language
;	O
namely	O
,	O
getting	O
the	O
process	B-Operating_System
startup	O
code	O
working	O
,	O
allowing	O
programs	O
to	O
run	O
,	O
thus	O
allowing	O
the	O
first	O
user	O
programs	O
(	O
trivial	O
ones	O
such	O
as	O
the	O
hello	O
world	O
program	O
)	O
in	O
C	B-Language
to	O
run	O
.	O
</s>
<s>
Since	O
2005	O
,	O
Brinkmann	O
and	O
Walfield	O
started	O
researching	O
Coyotos	B-Operating_System
as	O
a	O
new	O
kernel	B-Operating_System
for	O
HURD	B-Application
.	O
</s>
<s>
In	O
2006	O
,	O
Brinkmann	O
met	O
with	O
Jonathan	O
Shapiro	O
(	O
a	O
primary	O
architect	O
of	O
the	O
Coyotos	B-Operating_System
Operating	O
System	O
)	O
to	O
aid	O
in	O
and	O
discuss	O
the	O
use	O
of	O
the	O
Coyotos	B-Operating_System
kernel	B-Operating_System
for	O
GNU/Hurd	B-Application
.	O
</s>
<s>
In	O
further	O
discussion	O
HURD	B-Application
developers	O
realised	O
that	O
Coyotos	B-Operating_System
(	O
as	O
well	O
as	O
other	O
similar	O
kernels	B-Operating_System
)	O
are	O
not	O
suitable	O
for	O
HURD	B-Application
.	O
</s>
<s>
In	O
2007	O
,	O
Hurd	B-Application
developers	O
Neal	O
Walfield	O
and	O
Marcus	O
Brinkmann	O
gave	O
a	O
critique	O
of	O
the	B-Application
Hurd	I-Application
architecture	O
,	O
known	O
as	O
"	O
the	O
critique	O
"	O
,	O
and	O
a	O
proposal	O
for	O
how	O
a	O
future	O
system	O
may	O
be	O
designed	O
,	O
known	O
as	O
"	O
the	O
position	O
paper	O
"	O
.	O
</s>
<s>
In	O
2008	O
,	O
Neal	O
Walfield	O
began	O
working	O
on	O
the	O
Viengoos	O
microkernel	B-Operating_System
as	O
a	O
modern	O
native	O
kernel	B-Operating_System
for	O
HURD	B-Application
.	O
</s>
<s>
In	O
the	O
meantime	O
,	O
others	O
have	O
continued	O
working	O
on	O
the	O
Mach	B-Operating_System
variant	O
of	O
Hurd	B-Application
.	O
</s>
<s>
A	O
number	O
of	O
traditional	B-Application
Unix	I-Application
concepts	O
are	O
replaced	O
or	O
extended	O
in	O
the	B-Application
Hurd	I-Application
.	O
</s>
<s>
Under	O
Unix	B-Application
,	O
every	O
running	O
program	O
has	O
an	O
associated	O
user	B-Application
id	I-Application
,	O
which	O
normally	O
corresponds	O
to	O
the	O
user	O
that	O
started	O
the	O
process	B-Operating_System
.	O
</s>
<s>
No	O
outside	O
process	B-Operating_System
can	O
change	O
the	O
user	B-Application
id	I-Application
of	O
a	O
running	O
program	O
.	O
</s>
<s>
A	O
Hurd	B-Application
process	B-Operating_System
,	O
on	O
the	O
other	O
hand	O
,	O
runs	O
under	O
a	O
set	O
of	O
user	B-Application
ids	I-Application
,	O
which	O
can	O
contain	O
multiple	O
ids	O
,	O
one	O
,	O
or	O
none	O
.	O
</s>
<s>
A	O
sufficiently	O
privileged	O
process	B-Operating_System
can	O
add	O
and	O
remove	O
ids	O
to	O
another	O
process	B-Operating_System
.	O
</s>
<s>
Regarding	O
the	O
file	B-Application
system	I-Application
,	O
a	O
suitable	O
program	O
can	O
be	O
designated	O
as	O
a	O
translator	O
for	O
a	O
single	O
file	O
or	O
a	O
whole	O
directory	O
hierarchy	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
file	O
translator	O
may	O
simply	O
redirect	O
read	O
and	O
write	O
operations	O
to	O
another	O
file	O
,	O
like	O
a	O
Unix	B-Application
symbolic	B-Application
link	I-Application
.	O
</s>
<s>
The	O
effect	O
of	O
Unix	B-Application
mounting	B-Application
is	O
achieved	O
by	O
setting	O
up	O
a	O
filesystem	B-Application
translator	O
(	O
using	O
the	O
"	O
settrans	O
"	O
command	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
ftpfs	B-Application
translator	O
allows	O
a	O
user	O
to	O
encapsulate	O
remote	O
FTP	O
sites	O
within	O
a	O
directory	O
.	O
</s>
<s>
Then	O
,	O
standard	O
tools	O
such	O
as	O
ls	B-Application
,	O
cp	B-Application
,	O
and	O
rm	B-Application
can	O
be	O
used	O
to	O
manipulate	O
files	O
on	O
the	O
remote	O
system	O
.	O
</s>
<s>
Even	O
more	O
powerful	O
translators	O
are	O
ones	O
such	O
as	O
UnionFS	B-Application
,	O
which	O
allows	O
a	O
user	O
to	O
unify	O
multiple	O
directories	O
into	O
one	O
;	O
thus	O
listing	O
the	O
unified	O
directory	O
reveals	O
the	O
contents	O
of	O
all	O
the	O
directories	O
.	O
</s>
<s>
The	B-Application
Hurd	I-Application
requires	O
a	O
multiboot-compliant	O
boot	B-Operating_System
loader	I-Operating_System
,	O
such	O
as	O
GRUB	B-Application
.	O
</s>
<s>
According	O
to	O
the	O
Debian	O
documentation	O
,	O
there	O
are	O
24	O
servers	O
(	O
18	O
core	O
servers	O
and	O
6	O
file	B-Application
system	I-Application
servers	O
)	O
named	O
as	O
follows	O
:	O
</s>
<s>
auth	O
(	O
authentication	B-Application
server	I-Application
)	O
:	O
Receives	O
requests	O
and	O
passwords	O
from	O
programs	O
and	O
gives	O
them	O
an	O
ID	O
,	O
which	O
changes	O
the	O
privileges	O
of	O
the	O
program	O
.	O
</s>
<s>
crash	B-General_Concept
(	O
crash	B-General_Concept
server	O
)	O
:	O
Handles	O
all	O
fatal	O
errors	O
.	O
</s>
<s>
fifo	B-Operating_System
(	O
FIFO	B-Operating_System
translator	O
)	O
:	O
Implements	O
named	O
pipes	O
.	O
</s>
<s>
new-fifo	O
(	O
new	O
FIFO	B-Operating_System
server	O
)	O
:	O
An	O
alternate	O
server	O
for	O
named	O
pipes	O
.	O
</s>
<s>
firmlink	O
(	O
the	O
firmlink	O
translator	O
)	O
:	O
Implements	O
firmlinks	O
‒	O
"	O
half-way	O
between	O
a	O
symbolic	B-Application
link	I-Application
and	O
a	O
hard	B-Application
link	I-Application
"	O
.	O
</s>
<s>
fwd	O
(	O
forward	O
server	O
)	O
:	O
Forwards	O
requests	O
to	O
other	O
servers	O
,	O
used	O
by	O
fifo	B-Operating_System
and	O
symlink	B-Application
servers	O
.	O
</s>
<s>
ifsock	O
(	O
server	O
for	O
sockets	O
interface	O
)	O
:	O
Helps	O
with	O
UNIX	B-Protocol
domain	I-Protocol
socket	I-Protocol
addresses	O
.	O
</s>
<s>
init	B-Operating_System
(	O
init	B-Operating_System
server	O
)	O
:	O
Basic	O
system	O
booting	B-Operating_System
and	O
configuration	O
.	O
</s>
<s>
magic	O
(	O
magic	O
server	O
)	O
:	O
Signals	O
that	O
a	O
name	O
lookup	O
must	O
be	O
resolved	O
internally	O
by	O
a	O
process	B-Operating_System
when	O
the	O
result	O
involves	O
the	O
process	B-Operating_System
's	O
state	O
.	O
</s>
<s>
null	O
(	O
null	O
server	O
)	O
:	O
Implements	O
/dev/null	B-Operating_System
and	O
/dev/zero	O
.	O
</s>
<s>
pflocal	O
(	O
pflocal	O
server	O
)	O
:	O
Implements	O
UNIX	B-Protocol
domain	I-Protocol
sockets	I-Protocol
.	O
</s>
<s>
proc	O
(	O
process	B-Operating_System
server	O
)	O
:	O
Assigns	O
PIDs	B-Operating_System
and	O
manages	O
process-level	O
actions	O
.	O
</s>
<s>
symlink	B-Application
(	O
symbolic	B-Application
link	I-Application
translator	O
)	O
:	O
Implements	O
symbolic	B-Application
links	I-Application
for	O
filesystems	B-Application
that	O
do	O
n't	O
support	O
them	O
.	O
</s>
<s>
The	O
ext2	B-Application
filesystem	B-Application
translator	O
.	O
</s>
<s>
It	O
receives	O
disk	O
blocks	O
from	O
the	O
microkernel	B-Operating_System
and	O
gives	O
files	O
and	O
directories	O
to	O
the	O
applications	O
.	O
</s>
<s>
The	O
translator	O
for	O
the	O
ISO	B-Application
9660	I-Application
filesystem	B-Application
.	O
</s>
<s>
See	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
.	O
</s>
<s>
Translator	O
for	O
the	O
BSD	O
filesystem	B-Application
of	O
the	O
same	O
name	O
,	O
UFS	B-Operating_System
.	O
</s>
<s>
File	B-Protocol
transfer	I-Protocol
protocol	I-Protocol
filesystem	B-Application
translator	O
.	O
</s>
<s>
The	O
servers	O
collectively	O
implement	O
the	O
POSIX	O
API	B-Application
,	O
with	O
each	O
server	O
implementing	O
a	O
part	O
of	O
the	O
interface	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
various	O
filesystem	B-Application
servers	O
each	O
implement	O
the	O
filesystem	B-Application
calls	O
.	O
</s>
<s>
The	O
storage	O
server	O
will	O
work	O
as	O
a	O
wrapping	O
layer	O
,	O
similar	O
to	O
the	O
block	O
layer	O
of	O
Linux	B-Operating_System
.	O
</s>
<s>
The	O
equivalent	O
of	O
VFS	B-Application
of	O
Linux	B-Operating_System
is	O
achieved	O
by	O
libdiskfs	O
and	O
libpager	O
libraries	O
.	O
</s>
<s>
Hurd-based	O
GNU	B-Application
distributions	I-Application
include	O
:	O
</s>
