<s>
The	O
Network	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
daemon	B-Operating_System
(	O
ntpd	B-Protocol
)	O
is	O
an	O
operating	B-Operating_System
system	I-Operating_System
program	I-Operating_System
that	O
maintains	O
the	O
system	B-Operating_System
time	I-Operating_System
in	O
synchronization	O
with	O
time	B-Protocol
servers	I-Protocol
using	O
the	O
Network	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
(	O
NTP	O
)	O
.	O
</s>
<s>
The	O
ntpd	B-Protocol
program	O
is	O
an	O
operating-system	O
daemon	O
that	O
sets	O
and	O
maintains	O
a	O
computer	O
system	O
's	O
system	B-Operating_System
time	I-Operating_System
in	O
synchronization	O
with	O
Internet-standard	O
time	B-Protocol
servers	I-Protocol
.	O
</s>
<s>
It	O
is	O
a	O
complete	O
implementation	O
of	O
the	O
Network	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
(	O
NTP	O
)	O
version	O
4	O
,	O
but	O
retains	O
compatibility	O
with	O
versions	O
1	O
,	O
2	O
,	O
and	O
3	O
as	O
defined	O
by	O
RFC	O
1059	O
,	O
RFC	O
1119	O
,	O
and	O
RFC	B-Protocol
1305	I-Protocol
,	O
respectively	O
.	O
</s>
<s>
ntpd	B-Protocol
performs	O
most	O
computations	O
in	O
64-bit	O
floating	B-Algorithm
point	I-Algorithm
arithmetic	I-Algorithm
and	O
uses	O
64-bit	O
fixed	O
point	O
operations	O
only	O
when	O
necessary	O
to	O
preserve	O
the	O
ultimate	O
precision	B-General_Concept
,	O
about	O
232	O
picoseconds	O
.	O
</s>
<s>
While	O
ordinary	O
workstations	O
and	O
networks	O
cannot	O
achieve	O
the	O
ultimate	O
precision	B-General_Concept
,	O
future	O
processors	O
and	O
networks	O
may	O
require	O
it	O
.	O
</s>
<s>
xntpd	O
is	O
the	O
Network	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
version	O
three	O
(	O
1992	O
)	O
daemon	B-Operating_System
software	O
.	O
</s>
<s>
The	O
name	O
of	O
the	O
software	O
changed	O
back	O
to	O
"	O
ntpd	B-Protocol
"	O
for	O
version	O
four	O
because	O
the	O
inventor	O
of	O
NTP	O
,	O
Dave	O
Mills	O
,	O
decided	O
that	O
something	O
probably	O
should	O
not	O
remain	O
"	O
experimental	O
"	O
for	O
about	O
twenty	O
years	O
in	O
the	O
absence	O
of	O
dramatic	O
change	O
.	O
</s>
<s>
ntpd	B-Protocol
uses	O
a	O
single	O
configuration-file	O
to	O
run	O
the	O
daemon	B-Operating_System
in	O
server	O
and/or	O
client	O
modes	O
.	O
</s>
<s>
Other	O
important	O
files	O
include	O
the	O
drift	O
file	O
,	O
which	O
ntpd	B-Protocol
uses	O
to	O
correct	O
for	O
hardware-clock	O
skew	O
in	O
the	O
absence	O
of	O
a	O
connection	O
to	O
a	O
more	O
accurate	O
upstream	O
time-server	O
.	O
</s>
<s>
chrony	B-Application
chronyd	B-Application
implements	O
the	O
NTP	O
protocol	O
and	O
can	O
act	O
as	O
either	O
a	O
client	O
or	O
a	O
server	O
.	O
</s>
<s>
BusyBox	B-Application
,	O
since	O
version	O
1.16.2	O
,	O
has	O
included	O
an	O
SNTP	O
client	O
and	O
server	O
based	O
on	O
OpenNTP	B-Application
.	O
</s>
