On the internet there are time servers that provide the correct time. Your local network may provide such a server but most people need to access an NTP server via the internet. To set the time automatically you need access to an NTP server. ![]() The protocol used to set the time is the Network Time Protocol or NTP. This is done by the script /etc/init.d/hwclock.sh. Modern Debian releases (2.2 and onwards) automatically save the system time to hardware clock on proper shutdowns, and set the system clock from hardware clock when they boot up. To write the current system time to the hardware clock so that it can be recovered on subsequent restarts of the system, correct the system time as above, then use the command hwclock -systohc to save it to hardware (see the hwclock manual page for more options). See also the time-admin program in gnome-system-tools package. Most desktop environments provide a date/time configuration utility. When the system boots, it has no concept of absolute time and will populate the system time with the date and time read from the hardware clock, thus to ensure that the time set using date is kept across reboots it has to be saved to the hardware clock. software clock) but has no effect on the underlying hardware clock (aka. ![]() Note, using the date command only sets the runtime system time (aka. The above two commands set the system date to second of November, 1998, and system time to eight minutes past nine, PM. ![]() The -set argument examples below is specified in the ISO 8601 standard's extended format as YYYY-MM-DD for Year-Month-DayOfMonth, and time of day HH:MM:SS using 24 hour clock. You can read the man page of date, or use the example below for one possible and very useful format. However, when using the -set argument date accepts the date and time in many formats. When setting the system time manually using date directly, the required time specification format may be confusing (by POSIX convention has to be MMDDhhmmYYYY). To see the time in the UTC timezone, use the command date -utc (or shorthand date -u). To see the time on a Debian GNU/Linux system, use the command date, without arguments it will show system time respecting the currently defined timezone. Hardware clock and system time when dual booting.Furthermore, it also displays the currently configured time zone of the system (which is UTC by default in our images). The timedatectl allows displaying the current time, both, the system clock and the hardware clock. Note: To let one of the RTCs retain the time even when no power is applied to the system, put a backup battery in the respective holder on the carrier board. Traditionally, on power off, the system clock will get stored into the hardware clock by a shutdown script. You can display the current time, set a hardware clock to a specified time, set a hardware clock to the system time, and set the system time from the hardware clock. The system clock will not get stored into the hardware clock on shutdown.Īlternatively, there is the tool hwclock for accessing one of the hardware clocks directly. When using the timedatectl utility, the time will get stored into the hardware clock immediately when setting a new date or time. Our images use systemd-timedated and the timedatectl command since V2.1 and sytemd-timesyncd since V2.4 to synchronize time with a remote Network Time Protocol (NTP) server. ![]() From that point onward the system clock is used to track time. At boot time, the hardware clock is read and used to set the system clock. The second clock is called the ‘ system clock/tick’ or ' kernel clock' and is maintained by the operating system. This is the battery-backed clock that keeps time even when the system is shut down. Two clocks are important in Linux: a ‘ hardware clock’, also known as RTC, CMOS or BIOS clock. This article describes how to use a Real-Time Clock (RTC) on Embedded Linux. Is this page helpful? Real-Time Clock / RTC (Linux) Purpose
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