9.5. Configuring the system clock

This section discusses how to configure the systemd-timedated system service, which configures the system clock and timezone.

If you cannot remember whether or not the hardware clock is set to UTC, find out by running the hwclock --localtime --show 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 hwclock 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 hwclock. For example, if you are currently in the MST timezone, which is also known as GMT -0700, add seven hours to the local time.

systemd-timedated reads /etc/adjtime, and depending on the contents of the file, sets the clock to either UTC or local time.

Create the /etc/adjtime file with the following contents if your hardware clock is set to local time:

cat > /etc/adjtime << "EOF"
0.0 0 0.0

If /etc/adjtime isn't present at first boot, systemd-timedated will assume that hardware clock is set to UTC and adjust the file according to that.

You can also use the timedatectl utility to tell systemd-timedated if your hardware clock is set to UTC or local time:

timedatectl set-local-rtc 1

timedatectl can also be used to change system time and time zone.

To change your current system time, issue:

timedatectl set-time YYYY-MM-DD HH:MM:SS

The hardware clock will also be updated accordingly.

To change your current time zone, issue:

timedatectl set-timezone TIMEZONE

You can get a list of available time zones by running:

timedatectl list-timezones


Please note that the timedatectl command doesn't work in the chroot environment. It can only be used after the LFS system is booted with systemd.

9.5.1. Network Time Synchronization

Starting with version 213, systemd ships a daemon called systemd-timesyncd which can be used to synchronize the system time with remote NTP servers.

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.

Starting with systemd version 216, the systemd-timesyncd daemon is enabled by default. If you want to disable it, issue the following command:

systemctl disable systemd-timesyncd

The /etc/systemd/timesyncd.conf file can be used to change the NTP servers that systemd-timesyncd synchronizes with.

Please note that when system clock is set to Local Time, systemd-timesyncd won't update hardware clock.