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Synchronizing Time on Linux Servers

The most recommended approach for servers is to use NTP to ensure the time is always accurate and synchronized with external sources. Below we cover the recommended method to perform this configuration.

Section titled “Using chrony (Recommended for More Accurate Synchronization)”

chrony is often used on virtual machines or in environments with variable network time. It is common in RHEL/CentOS 7+ and some Ubuntu and Debian installations.

  1. Install chrony (if necessary):

    • Debian/Ubuntu: sudo apt update && sudo apt install chrony
    • RHEL/CentOS/Fedora: sudo dnf install chrony or sudo yum install chrony

  2. Start and Enable the Service:

    Terminal window
    sudo systemctl enable --now chronyd
    # or chrony for Debian/Ubuntu

  3. Check the Synchronization:

    Terminal window
    chronyc tracking

    Look for a Reference ID and a Stratum different from zero. The System time will show the offset.

Set Timezone

Section titled “Set Timezone”

First, set the correct timezone, as this affects the system clock.

  1. List Timezones:

    Terminal window
    timedatectl list-timezones | grep 'America/Sao_Paulo'

    (Replace with the desired timezone)

  2. Set the Timezone:

    Terminal window
    sudo timedatectl set-timezone 'America/Sao_Paulo'

  3. Verify that the time is correct:

    Terminal window
    date

Synchronize the Hardware Clock (CMOS/BIOS)

Section titled “Synchronize the Hardware Clock (CMOS/BIOS)”

The Linux server maintains two clocks: the System Clock (software) and the Hardware/BIOS Clock (CMOS, battery-backed). After fixing the system clock, synchronize it with the hardware clock so the time remains correct after a reboot.

Terminal window
sudo hwclock -w  # Writes System time (soft) to the Hardware (hard)