faraphel/chrony
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

doc: update comparison with ntpd

Browse source
This commit is contained in:
Miroslav Lichvar 2015-10-14 14:08:21 +02:00
parent da1f7563e9
commit 1924481077
1 changed files with 33 additions and 15 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

48
chrony.texi.in
View file

@ -137,9 +137,9 @@ The `reference' implementation of the Network Time Protocol is the
program @code{ntpd}, available via
@uref{http://www.ntp.org/, The NTP home page}.
One of the main differences between @code{ntpd} and @code{chronyd} is in
the algorithms used to control the computer's clock. Things
@code{chronyd} can do better than @code{ntpd}:
One of the main differences between @code{ntpd} and @code{chronyd} is in how
they control the computer's clock. Things @code{chronyd} can do better than
@code{ntpd}:
@itemize @bullet
@item
@ -159,13 +159,16 @@ longer periods of time.
@item
@code{chronyd} in the default configuration never steps the time to not
upset other running programs. @code{ntpd} can be configured to never
step the time too, but it has to use a different means of adjusting the
clock, which has some
disadvantages.
step the time too, but in that case it has to use a different means of
adjusting the clock (daemon loop instead of kernel discipline), which may
have a negative effect on accuracy of the clock.
@item
@code{chronyd} can adjust the rate of the clock in a larger range, which
allows it to operate even on machines with broken or unstable clock
(e.g. in some virtual machines).
@item
@code{chronyd} is smaller, it uses less memory and it wakes up the CPU only
when necessary, which is better for power saving.
@end itemize
Things @code{chronyd} can do that @code{ntpd} can't:
@ -191,21 +194,36 @@ Things @code{ntpd} can do that @code{chronyd} can't:
@itemize @bullet
@item
@code{ntpd} supports all operating modes from RFC 5905, including
broadcast, multicast and manycast client / server. It supports the
orphan mode and it also supports authentication based on public-key
cryptography described in RFC 5906.
@code{ntpd} supports all operating modes from RFC 5905, including broadcast,
multicast, and manycast server/client. However, the broadcast and multicast
modes are inherently less accurate and less secure (even with authentication)
than the ordinary server/client mode and should generally be avoided.
@item
@code{ntpd} has been ported to more types of computer / operating
system.
@code{ntpd} supports the Autokey protocol (RFC 5906) to authenticate servers
with public-key cryptography. Note that the protocol has been shown to be
insecure and it will be probably replaced with an implementation of the Network
Time Security (NTS) specification.
@item
@code{ntpd} includes drivers for many reference clocks. @code{chronyd}
relies on other programs (e.g. gpsd) to access the data from the
reference clocks.
@code{ntpd} supports the orphan mode, which allows synchronisation to a common
timescale in isolated networks with multiple servers. With @code{chronyd}
there can be only one master and all other computers have to be directly or
indirectly synchronised to it.
@item
@code{ntpd} has been ported to more operating systems.
@item
@code{ntpd} includes a large number of reference clock drivers. @code{chronyd}
relies on other programs (e.g. @code{gpsd}) to access the timing data via the
@code{SHM} or @code{SOCK} driver.
@end itemize
A comparison of NTP implementations that includes more features and also
their performance is on the @uref{http://chrony.tuxfamily.org/comparison.html,
chrony comparison} page.
@node Comparison with timed
@subsection timed
@code{timed} is a program that is part of the BSD networking suite. It