<s>
OpenNTPD	B-Application
(	O
also	O
known	O
as	O
OpenBSD	B-Operating_System
NTP	B-Protocol
Daemon	I-Protocol
)	O
is	O
a	O
Unix	B-Operating_System
daemon	I-Operating_System
implementing	O
the	O
Network	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
to	O
synchronize	O
the	O
local	O
clock	O
of	O
a	O
computer	O
system	O
with	O
remote	O
NTP	B-Protocol
servers	I-Protocol
.	O
</s>
<s>
It	O
is	O
also	O
able	O
to	O
act	O
as	O
an	O
NTP	B-Protocol
server	I-Protocol
to	O
NTP-compatible	O
clients	O
.	O
</s>
<s>
OpenBSD	B-Operating_System
NTP	B-Protocol
Daemon	I-Protocol
was	O
initially	O
developed	O
by	O
Alexander	O
Guy	O
and	O
Henning	O
Brauer	O
as	O
part	O
of	O
the	O
OpenBSD	B-Operating_System
project	I-Operating_System
,	O
with	O
further	O
help	O
by	O
many	O
authors	O
.	O
</s>
<s>
Its	O
portable	O
version	O
,	O
like	O
that	O
of	O
OpenSSH	B-Language
,	O
is	O
developed	O
as	O
a	O
child	O
project	O
which	O
adds	O
the	O
portability	O
code	O
to	O
the	O
OpenBSD	B-Operating_System
version	O
and	O
releases	O
it	O
separately	O
.	O
</s>
<s>
The	O
project	O
developers	O
receive	O
some	O
funding	O
from	O
the	O
OpenBSD	B-Operating_System
Foundation	O
.	O
</s>
<s>
The	O
development	O
of	O
OpenNTPD	B-Application
was	O
motivated	O
by	O
a	O
combination	O
of	O
issues	O
with	O
current	O
NTP	O
daemons	B-Operating_System
:	O
difficult	O
configuration	O
,	O
complicated	O
and	O
difficult	O
to	O
audit	O
code	O
,	O
and	O
unsuitable	O
licensing	O
.	O
</s>
<s>
OpenNTPD	B-Application
was	O
designed	O
to	O
solve	O
these	O
problems	O
and	O
make	O
time	B-Protocol
synchronization	I-Protocol
accessible	O
to	O
a	O
wider	O
userbase	O
.	O
</s>
<s>
After	O
a	O
period	O
of	O
development	O
,	O
OpenNTPD	B-Application
first	O
appeared	O
in	O
OpenBSD	B-Operating_System
3.6	O
.	O
</s>
<s>
OpenNTPD	B-Application
is	O
an	O
attempt	O
by	O
the	O
OpenBSD	B-Operating_System
team	O
to	O
produce	O
an	O
NTP	B-Protocol
daemon	I-Protocol
implementation	O
that	O
is	O
secure	O
,	O
simple	O
to	O
audit	O
,	O
trivial	O
to	O
set	O
up	O
and	O
administer	O
,	O
reasonably	O
accurate	O
,	O
and	O
light	O
on	O
system	O
resources	O
.	O
</s>
<s>
As	O
such	O
,	O
the	O
design	O
goals	O
for	O
OpenNTPD	B-Application
are	O
:	O
security	O
,	O
ease	O
of	O
use	O
,	O
and	O
performance	O
.	O
</s>
<s>
Security	O
in	O
OpenNTPD	B-Application
is	O
achieved	O
by	O
robust	O
validity	O
check	O
in	O
the	O
network	O
input	O
path	O
,	O
use	O
of	O
bounded	O
buffer	O
operations	O
via	O
strlcpy	O
,	O
and	O
privilege	O
separation	O
to	O
mitigate	O
the	O
effects	O
of	O
possible	O
security	O
bugs	O
exploiting	O
the	O
daemon	B-Operating_System
through	O
privilege	O
escalation	O
.	O
</s>
<s>
In	O
order	O
to	O
simplify	O
the	O
use	O
of	O
NTP	O
,	O
OpenNTPD	B-Application
implements	O
a	O
smaller	O
set	O
of	O
functionalities	O
than	O
those	O
available	O
in	O
other	O
NTP	O
daemons	B-Operating_System
,	O
such	O
as	O
that	O
provided	O
by	O
the	O
Network	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
Project	O
.	O
</s>
<s>
OpenNTPD	B-Application
is	O
configured	O
through	O
the	O
configuration	O
file	O
,	O
ntpd.conf	O
.	O
</s>
<s>
A	O
minimal	O
number	O
of	O
options	O
are	O
offered	O
:	O
IP	O
address	O
or	O
hostname	O
on	O
which	O
OpenNTPD	B-Application
should	O
listen	O
,	O
a	O
timedelta	O
sensor	O
device	O
to	O
be	O
used	O
,	O
and	O
the	O
set	O
of	O
servers	O
from	O
which	O
the	O
time	O
will	O
be	O
synchronized	O
.	O
</s>
<s>
The	O
accuracy	O
of	O
OpenNTPD	B-Application
is	O
best-effort	O
;	O
the	O
daemon	B-Operating_System
attempts	O
to	O
be	O
as	O
accurate	O
as	O
possible	O
but	O
no	O
specific	O
accuracy	O
is	O
guaranteed	O
.	O
</s>
<s>
OpenNTPD	B-Application
gradually	O
adjusts	O
the	O
system	O
clock	O
,	O
as	O
seen	O
here	O
in	O
the	O
output	O
of	O
OpenNTPD	B-Application
running	O
on	O
a	O
Linux	B-Application
system	O
:	O
</s>
<s>
OpenNTPD	B-Application
has	O
been	O
criticized	O
as	O
being	O
less	O
accurate	O
than	O
the	O
NTP	B-Protocol
daemon	I-Protocol
produced	O
by	O
the	O
NTP	O
Project	O
(	O
ntp.org	O
)	O
.	O
</s>
<s>
Internally	O
,	O
OpenNTPD	B-Application
does	O
not	O
maintain	O
millisecond	O
accuracy	O
and	O
can	O
vary	O
50-200ms	O
from	O
"	O
real	O
"	O
time	O
because	O
it	O
omits	O
a	O
variety	O
of	O
algorithms	O
that	O
increase	O
accuracy	O
in	O
favour	O
of	O
code	O
simplicity	O
.	O
</s>
<s>
The	O
OpenNTPD	B-Application
project	O
acknowledged	O
the	O
criticism	O
,	O
but	O
stated	O
that	O
the	O
lack	O
of	O
microsecond	O
precision	O
was	O
a	O
design	O
tradeoff	O
that	O
benefited	O
simplicity	O
and	O
security	O
.	O
</s>
<s>
The	O
OpenNTPD	B-Application
design	O
goals	O
state	O
the	O
project	O
's	O
intent	O
is	O
to	O
"[r]each	O
a	O
reasonable	O
accuracy	O
"	O
without	O
sacrificing	O
"	O
secure	O
design	O
for	O
getting	O
that	O
last	O
nanosecond	O
or	O
obscure	O
edge	O
case.	O
"	O
</s>
<s>
In	O
September	O
2004	O
,	O
shortly	O
after	O
the	O
release	O
of	O
OpenNTPD	B-Application
3.6	O
,	O
ntp.org	O
contributor	O
Brad	O
Knowles	O
published	O
an	O
article	O
entitled	O
OpenNTPd	B-Application
Considered	O
Harmful	O
criticizing	O
various	O
aspects	O
of	O
OpenNTPD	B-Application
's	O
implementation	O
of	O
the	O
NTP	O
protocol	O
,	O
as	O
well	O
as	O
the	O
split	O
development	O
model	O
that	O
the	O
project	O
employs	O
,	O
which	O
is	O
also	O
used	O
in	O
the	O
development	O
of	O
OpenSSH	B-Language
and	O
OpenBGPD	B-Application
.	O
</s>
<s>
In	O
December	O
2004	O
,	O
Darren	O
Tucker	O
,	O
the	O
principal	O
developer	O
on	O
the	O
portable	O
branch	O
of	O
OpenNTPD	B-Application
,	O
wrote	O
a	O
detailed	O
response	O
to	O
Knowles	O
,	O
acknowledging	O
some	O
issues	O
as	O
valid	O
,	O
rejecting	O
several	O
others	O
as	O
unwarranted	O
,	O
and	O
considering	O
yet	O
others	O
as	O
misleading	O
.	O
</s>
<s>
Among	O
the	O
more	O
serious	O
issues	O
raised	O
by	O
Knowles	O
was	O
that	O
OpenNTPD	B-Application
servers	O
claimed	O
to	O
be	O
stratum	O
1	O
servers	O
.	O
</s>
<s>
Additionally	O
,	O
the	O
OpenBSD	B-Operating_System
networking	O
FAQ	O
was	O
expanded	O
with	O
a	O
response	O
to	O
Knowles	O
 '	O
initial	O
criticism	O
.	O
</s>
<s>
The	O
current	O
OpenNTPD	B-Application
accuracy	O
claim	O
is	O
,	O
from	O
the	O
2004	O
21C3	O
presentation	O
,	O
"	O
typically	O
50ms	O
"	O
.	O
</s>
<s>
OpenNTPD	B-Application
(	O
and	O
the	O
OpenBSD	B-Operating_System
kernel	O
)	O
ignore	O
leap	O
seconds	O
.	O
</s>
<s>
Care	O
should	O
be	O
taken	O
when	O
using	O
OpenNTPD	B-Application
as	O
a	O
higher-stratum	O
source	O
for	O
other	O
ntpd	B-Protocol
servers	O
,	O
or	O
with	O
high-resolution	O
time	O
requirements	O
that	O
reference	O
Coordinated	O
Universal	O
Time	O
.	O
</s>
