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diff --git a/chapter07/clock.xml b/chapter07/clock.xml new file mode 100644 index 000000000..0dbdc7eaf --- /dev/null +++ b/chapter07/clock.xml @@ -0,0 +1,104 @@ +<?xml version="1.0" encoding="ISO-8859-1"?> +<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" + "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [ + <!ENTITY % general-entities SYSTEM "../general.ent"> + %general-entities; +]> + +<sect1 id="ch-scripts-clock"> + <?dbhtml filename="clock.html"?> + + <title>Configuring the system clock</title> + + <indexterm zone="ch-scripts-clock"> + <primary sortas="d-clock">clock</primary> + <secondary>configuring</secondary></indexterm> + + <para>This section discusses how to configure the + <command>systemd-timedated</command> system service, which configures + system clock and timezone.</para> + + <para>If you cannot remember whether or not the hardware clock is set to UTC, + find out by running the <userinput>hwclock --localtime --show</userinput> + command. This will display what the current time is according to the hardware + clock. If this time matches whatever your watch says, then the hardware clock is + set to local time. If the output from <command>hwclock</command> is not local + time, chances are it is set to UTC time. Verify this by adding or subtracting + the proper amount of hours for the timezone to the time shown by + <command>hwclock</command>. For example, if you are currently in the MST + timezone, which is also known as GMT -0700, add seven hours to the local + time.</para> + + <para><command>systemd-timedated</command> reads <filename>/etc/adjtime</filename>, + and depending on the contents of the file, it sets the clock to either UTC or + local time.</para> + + <para>Create the <filename>/etc/adjtime</filename> file with the following contents + if your hardware clock is set to local time:</para> + +<screen role="nodump"><userinput>cat > /etc/adjtime << "EOF" +<literal>0.0 0 0.0 +0 +LOCAL</literal> +EOF</userinput></screen> + + <para>If <filename>/etc/adjtime</filename> isn't present at first boot, + <command>systemd-timedated</command> will assume that hardware clock is + set to UTC and adjust the file according to that.</para> + + <para>You can also use the <command>timedatectl</command> utility to tell + <command>systemd-timedated</command> if your hardware clock is set to + UTC or local time:</para> + +<screen role="nodump"><userinput>timedatectl set-local-rtc 1</userinput></screen> + + <para><command>timedatectl</command> can also be used to change system time and + time zone.</para> + + <para>To change your current system time, issue:</para> + +<screen role="nodump"><userinput>timedatectl set-time YYYY-MM-DD HH:MM:SS</userinput></screen> + + <para>Hardware clock will also be updated accordingly.</para> + + <para>To change your current time zone, issue:</para> + +<screen role="nodump"><userinput>timedatectl set-timezone TIMEZONE</userinput></screen> + + <para>You can get list of available time zones by running:</para> + +<screen role="nodump"><userinput>timedatectl list-timezones</userinput></screen> + + <note><para>Please note that <command>timedatectl</command> command can + be used only on a system booted with systemd.</para></note> + + <sect2> + <title>Network Time Synchronization</title> + + <para>Starting with version 213, systemd ships a daemon called + <command>systemd-timesyncd</command> which can be used to + synchronize the system time with remote NTP servers.</para> + + <para>The daemon is not intended as a replacement for the well + established NTP daemon, but as a client only implementation + of the SNTP protocol which can be used for less advanced + tasks and on resource limited systems.</para> + + <para>Starting with systemd version 216, the + <command>systemd-timesyncd</command> daemon is enabled by + default. If you want to disable it, issue the following + command:</para> + +<screen role="nodump"><userinput>systemctl disable systemd-timesyncd</userinput></screen> + + <para>The <filename>/etc/systemd/timesyncd.conf</filename> file + can be used to change the NTP servers that + <command>systemd-timesyncd</command> synchronizes with.</para> + + <para>Please note that when system clock is set to Local Time, + <command>systemd-timesyncd</command> won't update hardware + clock.</para> + + </sect2> + +</sect1> |