But, since we gave –test it will not really make the change, but it will still execute the command without any issues. The –systz option will change the system timezone accordingly. When you change things using hwclock, using –test option, you can execute the command without really making any changes. i.e number of seconds since 1969 UTC of recent adjustment Line 2 is the same value that you see in the 1st line, 2nd value.The three values in the 1st line represents 1) systematic drift rate in seconds per day, 2) number of seconds since 1969 UTC of recent adjustment 3) just 0.The /etc/adjtime file has the following three lines. The /etc/adjtime file is used by the hwclock –adjust option to control the adjustment. When the system starts, it takes the time from the hardware clock. (and thus is presumably not running on an Alpha now). This copy of hwclock was built for a machine other than Alpha

The kernel keeps an epoch value for the Hardware Clock only on an Alpha machine. When you try to run this on a on Alpha machine, you’ll get the following error machine. Note: On alpha machines you can use getepoch to view the epoch, setepoch to set the epoch.

Time read from Hardware Clock: 0 15:23:20 Last calibration done at 1375975224 seconds after 1969 Last drift adjustment done at 1375975224 seconds after 1969 The following shows exactly what it does when we copy hardware time to system time. Not adjusting drift factor because it has been less than a day since the last calibration. Time elapsed since reference time has been 0.009002 seconds. Time read from Hardware Clock: 0 15:16:37 Last calibration done at 1375974983 seconds after 1969Īssuming hardware clock is kept in UTC time. Last drift adjustment done at 1375974983 seconds after 1969 The following shows exactly what it does when we copy system time to hardware time. When you pass –debug option to the hwclock, it displays some debug information, which shows exactly what hwclock command does. While testing this, if you’ve messed-up your system time, you can use the date command examples to set it to correct date and time. –hctosys stands for “hardware clock to system”, which copies the time from hardware clock to system clock. I like to use –hctosys as it is easy to remember. Note: Both -s and –hctosys option does the same. When your hardware clock shows the correct date and time, but not your system clock, you can use -s option as shown below to copy the hardware time to system time as shown below. You can also take the output of the date command, and pass it to the –set and –date option as shown below. Please note that it will use the local time by default. You can also set both date and time at the same time as shown below. Please note that if you don’t specify the time, it will be set to 12:00:00 AM. The following will set the date to Aug 11th, 2013. Instead of copying the system date and time to the hardware clock, you can also manually set the value using –set and –date option as shown below. Set Hardware Clock Date and Time Manually –systohc stands for “system to hardware clock”, which copies the time from system to hardware clock. I like to use –systohc as it is easy to remember. Note: Both -w and –systohc option does the same. This is the typical use of the hwclock command. So, use the hwclock command as shown below to set the hardware clock same as system clock. You really want to make sure your hardware clock has the same date and time as the system clock.Īs you see currently there is a difference between the system clock and hardware clock time. This in example, there is around 10 mins difference between them. But, the date command gets the date and time from the clock managed from Linux kernel. Note: The output of the date command might be same as the output of the hwclock command (actually it should be the same). You can also use option -r, or –show to display the date and time. This is the same date and time that you’ll see from the BIOS screen.

Just type hwclock, which will display the date and time of your system’s hardware clock. However, when the system is up and running, you can still view and set the hardware date and time using Linux hwclock command as explained in this tutorial. You can change the date and time of the hardware clock from the BIOS. Hardware clock is also called as BIOS clock. Hardware clock runs even when you shutdown your system. The clock that is managed by Linux kernel is not the same as the hardware clock.

Set alarm time on dclock linux