22.5. UTC, Timezones, and DST

As NTP is entirely in UTC (Universal Time, Coordinated), Timezones and DST (Daylight Saving Time) are applied locally by the system. The file /etc/localtime is a copy of, or symlink to, a zone information file from /usr/share/zoneinfo. The RTC may be in localtime or in UTC, as specified by the 3rd line of /etc/adjtime, which will be one of LOCAL or UTC to indicate how the RTC clock has been set. Users can easily change this setting using the check box System Clock Uses UTC in the system-config-date graphical configuration tool. See Chapter 2, Date and Time Configuration for information on how to use that tool. Running the RTC in UTC is recommended to avoid various problems when daylight saving time is changed.
The operation of ntpd is explained in more detail in the man page ntpd(8). The resources section lists useful sources of information. See Section 22.19, “Additional Resources”.