fake-hwclock

Some machines don’t have a working realtime clock (RTC) unit, or no driver for the hardware that does exist. fake-hwclock is a simple set of scripts to save the kernel’s current clock periodically (including at shutdown) and restore it at boot so that the system clock keeps at least close to realtime. This will stop some of the problems that may be caused by a system believing it has travelled in time back to 1970, such as needing to perform filesystem checks at every boot.

On top of this, use of NTP is still recommended to deal with the fake clock “drifting” while the hardware is halted or rebooting.

Installed size: 32 KB
How to install: sudo apt install fake-hwclock

fake-hwclock

Control fake hardware clock

[email protected]:~# man fake-hwclock
FAKE-HWCLOCK(8)             System Manager's Manual            FAKE-HWCLOCK(8)

NAME
       fake-hwclock - Control fake hardware clock

SYNOPSIS
       fake-hwclock [ command ] [ force ]

BACKGROUND
       Many  embedded  Linux  systems do not have a functional hardware clock.
       Either they simply don't have a hardware clock at all or  they  have  a
       hardware  clock  but  it is not usable (e.g. because Linux doesn't know
       how to use it or because no battery is present).

       This can lead to time moving backwards to  some  default  value  (often
       1970)  when the system is rebooted. Since lots of software assumes that
       time only moves forward this is a bad thing. NTP can (and should  where
       practical)  be  used  to sync with an external timeserver but it is not
       available early in the boot process and may be  unavailable  for  other
       reasons.

       The design expectation of fake-hwclock is that it will be run very late
       at shutdown and very early at boot. This will ensure that  fsck  has  a
       vaguely  sensible  idea  of system time at boot and won't complain that
       the last-modified time in the filesystem is not hugely in the  past  or
       future. Some users may not worry about this too use case, in which case
       it is possible to modify the init system configuration to  move  things
       earlier/later as appropriate.

DESCRIPTION
       fake-hwclock  sets and queries a fake "hardware clock" which stores the
       time in a file. This program may be run by the system administrator di-
       rectly  but  is  typically run by init (to load the time on startup and
       save it on shutdown) and cron (to save the time hourly).

       If no command is given then fake-hwclock acts as if  the  save  command
       was used.

COMMANDS
       save   Save  the time to the file. As a sanity check, fake-hwclock will
              not move the saved clock backwards to a time/date  earlier  than
              its own release date. Use "force" to over-ride this check.

       load   Load  the time from the file. If force is specified fake-hwclock
              will move the clock either backwards or forwards.  Otherwise  it
              will only move it forwards.

FILES
       /etc/fake-hwclock.data
              The file used to store the time

       /etc/init.d/fake-hwclock
              The init script used to run fake-hwclock on startup and shutdown

       /lib/systemd/system/fake-hwclock.service
              systemd service used to run fake-hwclock on startup and shutdown

       /etc/default/fake-hwclock
              Settings file for the init script.

       /etc/cron.hourly/fake-hwclock
              Cron job used to save the time hourly

ENVIRONMENT VARIABLES
       FILE   set the file used by fake-hwclock

RETURN VALUES
       1 is returned for invalid commands. 0 is returned in all other cases.

BUGS
       This  approach  can  only  provide a crude approximation of what a real
       hardware clock provides. Use of NTP or another method to keep the  time
       in sync is strongly advised.

Debian                          1 October 2014                 FAKE-HWCLOCK(8)