[system-administrators-guide] systemd was changed couple releases ago to not sync the RTC on shutdown en-US/Configuring_NTP_Using_
commit 95adf27624cb18174f71a586db099257f556a54e
Author: Stephen Wadeley <swadeley(a)redhat.com>
Date: Tue Nov 12 10:03:48 2013 +0100
systemd was changed couple releases ago to not sync the RTC on shutdown
en-US/Configuring_NTP_Using_ntpd.xml
en-US/Configuring_NTP_Using_ntpd.xml | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/en-US/Configuring_NTP_Using_ntpd.xml b/en-US/Configuring_NTP_Using_ntpd.xml
index 3783a66..40b5a20 100644
--- a/en-US/Configuring_NTP_Using_ntpd.xml
+++ b/en-US/Configuring_NTP_Using_ntpd.xml
@@ -17,7 +17,7 @@
Accurate time keeping is important for a number of reasons in IT. In networking for
example, accurate time stamps in packets and logs are required. Logs are used to
investigate service and security issues and so timestamps made on different systems must
be made by synchronized clocks to be of real value. As systems and networks become
increasingly faster, there is a corresponding need for clocks with greater accuracy and
resolution. In some countries there are legal obligations to keep accurately synchronized
clocks. Please see <citetitle
pubwork="webpage">www.ntp.org</citetitle> for more information. In
Linux systems, <systemitem class="protocol">NTP</systemitem> is
implemented by a daemon running in user space. The default <systemitem
class="protocol">NTP</systemitem> user space daemon in &MAJOROSVER;
is <systemitem class="service">chronyd</systemitem>. It must be
disabled if you want to use the <systemitem
class="service">ntpd</systemitem> daemon. See <xref linkend=
"ch-Configuring_NTP_Using_the_chrony_Suite" /> for information on
<application>chrony</application>.
</para>
<para>
- The user space daemon updates the system clock, which is a software clock running
in the kernel. Linux uses a software clock as its system clock for better resolution than
the typical embedded hardware clock referred to as the <quote><firstterm>Real
Time Clock</firstterm></quote> <acronym>(RTC)</acronym>. See the
<filename>rtc(4)</filename> and <filename>hwclock(8)</filename>
man pages for information on hardware clocks. The system clock can keep time by using
various clock sources. Usually, the <firstterm>Time Stamp Counter</firstterm>
(<acronym>TSC</acronym>) is used. The TSC is a CPU register which counts the
number of cycles since it was last reset. It is very fast, has a high resolution, and
there are no interrupts. On system start, the system clock reads the time and date from
the RTC. The time kept by the RTC will drift away from actual time by up to 5 minutes per
month due to temperature variations. Hence the need for the system clock to be constantly
synchroni
zed with external time references and to update the RTC on system shut down. When the
system clock is being synchronized by <systemitem
class="service">ntpd</systemitem>, the kernel will in turn update the
RTC every 11 minutes automatically.
+ The user space daemon updates the system clock, which is a software clock running
in the kernel. Linux uses a software clock as its system clock for better resolution than
the typical embedded hardware clock referred to as the <quote><firstterm>Real
Time Clock</firstterm></quote> <acronym>(RTC)</acronym>. See the
<filename>rtc(4)</filename> and <filename>hwclock(8)</filename>
man pages for information on hardware clocks. The system clock can keep time by using
various clock sources. Usually, the <firstterm>Time Stamp Counter</firstterm>
(<acronym>TSC</acronym>) is used. The TSC is a CPU register which counts the
number of cycles since it was last reset. It is very fast, has a high resolution, and
there are no interrupts. On system start, the system clock reads the time and date from
the RTC. The time kept by the RTC will drift away from actual time by up to 5 minutes per
month due to temperature variations. Hence the need for the system clock to be constantly
synchroni
zed with external time references. When the system clock is being synchronized by
<systemitem class="service">ntpd</systemitem>, the kernel will in
turn update the RTC every 11 minutes automatically.
</para>
</section>