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106 lines
4.2 KiB
XML
106 lines
4.2 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-config-clock" revision="systemd">
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<?dbhtml filename="clock.html"?>
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<title>Configuring the System Clock</title>
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<indexterm zone="ch-config-clock">
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<primary sortas="d-clock">clock</primary>
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<secondary>configuring</secondary></indexterm>
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<para>This section discusses how to configure the
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<command>systemd-timedated</command> system service, which configures
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the system clock and timezone.</para>
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<para>If you cannot remember whether or not the hardware clock is set to UTC,
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find out by running the <userinput>hwclock --localtime --show</userinput>
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command. This will display what the current time is according to the hardware
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clock. If this time matches whatever your watch says, then the hardware clock is
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set to local time. If the output from <command>hwclock</command> is not local
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time, chances are it is set to UTC time. Verify this by adding or subtracting
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the proper amount of hours for the timezone to the time shown by
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<command>hwclock</command>. For example, if you are currently in the MST
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timezone, which is also known as GMT -0700, add seven hours to the local
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time.</para>
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<para><command>systemd-timedated</command> reads <filename>/etc/adjtime</filename>,
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and depending on the contents of the file, sets the clock to either UTC or
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local time.</para>
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<para>Create the <filename>/etc/adjtime</filename> file with the following contents
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if your hardware clock is set to local time:</para>
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<screen><userinput>cat > /etc/adjtime << "EOF"
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<literal>0.0 0 0.0
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0
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LOCAL</literal>
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EOF</userinput></screen>
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<para>If <filename>/etc/adjtime</filename> isn't present at first boot,
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<command>systemd-timedated</command> will assume that hardware clock is
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set to UTC and adjust the file according to that.</para>
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<para>You can also use the <command>timedatectl</command> utility to tell
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<command>systemd-timedated</command> if your hardware clock is set to
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UTC or local time:</para>
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<screen role="nodump"><userinput>timedatectl set-local-rtc 1</userinput></screen>
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<para><command>timedatectl</command> can also be used to change system time and
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time zone.</para>
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<para>To change your current system time, issue:</para>
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<screen role="nodump"><userinput>timedatectl set-time YYYY-MM-DD HH:MM:SS</userinput></screen>
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<para>The hardware clock will also be updated accordingly.</para>
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<para>To change your current time zone, issue:</para>
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<screen role="nodump"><userinput>timedatectl set-timezone TIMEZONE</userinput></screen>
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<para>You can get a list of available time zones by running:</para>
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<screen role="nodump"><userinput>timedatectl list-timezones</userinput></screen>
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<note><para>Please note that the <command>timedatectl</command> command
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doesn't work in the chroot environment. It can only
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be used after the LFS system is booted with systemd.</para></note>
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<sect2>
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<title>Network Time Synchronization</title>
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<para>Starting with version 213, systemd ships a daemon called
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<command>systemd-timesyncd</command> which can be used to
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synchronize the system time with remote NTP servers.</para>
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<para>The daemon is not intended as a replacement for the well
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established NTP daemon, but as a client only implementation
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of the SNTP protocol which can be used for less advanced
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tasks and on resource limited systems.</para>
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<para>Starting with systemd version 216, the
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<command>systemd-timesyncd</command> daemon is enabled by
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default. If you want to disable it, issue the following
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command:</para>
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<screen role="nodump"><userinput>systemctl disable systemd-timesyncd</userinput></screen>
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<para>The <filename>/etc/systemd/timesyncd.conf</filename> file
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can be used to change the NTP servers that
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<command>systemd-timesyncd</command> synchronizes with.</para>
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<para>Please note that when system clock is set to Local Time,
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<command>systemd-timesyncd</command> won't update hardware
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clock.</para>
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</sect2>
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</sect1>
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