hwclock

hwclock is an administration tool for the time clocks. It can display the Hardware Clock time and set the Hardware Clock. Run the command with sudo before it, or by root user, as it can be executed only by the superuser.

Command Syntax

Under Linux bash, use the following format,

hwclock [function] [option...]

Parameter

Parameter	Description
function:
-h, --help	Show help text and exit.
-r, --show	Read hardware clock and print result.
--set	Set the RTC to the time given with –date.
-s, --hctosys	Set the system time from the hardware clock.
-w, --systohc	Set the hardware clock from the current system time.
--systz	Set the system time based on the current timezone.
--adjust	Adjust the RTC to account for systematic drift since the clock was last set or adjusted.
--getepoch	Print out the kernel's hardware clock epoch value.
--setepoch	Set the kernel's hardware clock epoch value to the value given with –epoch.
--predict	Predict RTC reading at time given with –date.
-V, --version	Display version information and exit.
option:
-u, --utc	The hardware clock is kept in UTC.
--localtime	The hardware clock is kept in local time.
-f, --rtc <file>	Special /dev/... file to use instead of default.
--directisa	Access the ISA bus directly instead of /dev/rtc.
--badyear	Ignore RTC's year because the BIOS is broken.
--date <time>	Specifies the time to set the hardware clock to.
--epoch <year>	Specifies the year which is the beginning of the hardware clock's epoch value.
--noadjfile	Do not access /etc/adjtime; this requires the use of either --utc or –localtime.
--adjfile <file>	Specifies the path to the adjust file; the default is /etc/adjtime.
--test	Do not update anything, just show what would happen.
-D, --debug	Debugging mode.

Example

Show the help information of hwclock command.

admin@193:/$ sudo hwclock -h
Usage:
 hwclock [function] [option...]

Functions:
 -h, --help           show this help text and exit
 -r, --show           read hardware clock and print result
     --set            set the RTC to the time given with --date
 -s, --hctosys        set the system time from the hardware clock
 -w, --systohc        set the hardware clock from the current system time
     --systz          set the system time based on the current timezone
     --adjust         adjust the RTC to account for systematic drift since
                        the clock was last set or adjusted
     --getepoch       print out the kernel's hardware clock epoch value
     --setepoch       set the kernel's hardware clock epoch value to the
                        value given with --epoch
     --predict        predict RTC reading at time given with --date
 -V, --version        display version information and exit

Options:
 -u, --utc            the hardware clock is kept in UTC
     --localtime      the hardware clock is kept in local time
 -f, --rtc <file>     special /dev/... file to use instead of default
     --directisa      access the ISA bus directly instead of /dev/rtc
     --badyear        ignore RTC's year because the BIOS is broken
     --date <time>    specifies the time to which to set the hardware clock
     --epoch <year>   specifies the year which is the beginning of the
                        hardware clock's epoch value
     --noadjfile      do not access /etc/adjtime; this requires the use of
                        either --utc or --localtime
     --adjfile <file> specifies the path to the adjust file;
                        the default is /etc/adjtime
     --test           do not update anything, just show what would happen
 -D, --debug          debugging mode

Display hardware clock time.

admin@193:/$ sudo hwclock --show
Thu Jan 11 21:51:15 2001  -0.719120 seconds