This is fake hwclock(8) tool which emulates behavior of original hwclock, but just
saves to or reads from a static file current datetime stamp. By default, it uses
/etc/fakehwclock.sav file, which is small binary file that contains dump of
struct timespec plus some identifying header and padding for future use.
To tell simply: this tool shall not be used on "normal" systems with /dev/rtc0 available (i.e. which contains typically battery powered Real Time Clock). Those which don't (e.g. vanilla Raspberry PI without addons) could use this tool just so their bootup time is not stuck in somewhere deep Unix past (01-01-1970).
Just type make, you'll need at least gcc for this. Code is simple. It shall
not encounter any troubles building it (unless it'll become very outdated in future).
Typing make install will move your distro shipped /sbin/hwclock to a /sbin/hwclock.orig
backup, so you'll not loose it if you in future will need it again. The new binary
will be placed on it's place.
Untill now on don't touch it, typically your distro init scripts (or whatever) will
call it with standard arguments on reboot/shutdown and only then /etc/fakehwclock.sav
will appear. On next boot, init scripts will call it again to obtain value from
that /etc/fakehwclock.sav file which was saved previously, and expected to set
clocks at least point of last shutdown time. Use ntpd to correct clocks after that.
That's it.
The process is automated (provided that your init scripts will call it with correct arguments) and confirmed working for me in Slackware on an VisionFive V1 RISC-V board.
systemd. I dunno how it manages this problem on RTC-less systems, it's huge clusterfuck. I don't want to poke into it if it works or not. You can try and report (funny) results.
Time drifts and other timekeeping/NTP trickery is not supported at the moment. (and probably never will)
Most (if not all) command line arguments of standard hwclock(8) are accepted, but many are simply ignored. The only operations supported by now are:
-r: read/etc/fakehwclock.savand report timestamp it contains in hwclock(8) format,-w: saving system time to/etc/fakehwclock.sav,-s: loading last saved timestamp from/etc/fakehwclock.sav,-u: giving program a hint it shall save as UTC,-l: giving program a hint it shall save as localtime.
Long options such as --show for -r are also supported.
/etc/fakehwclock.sav is binary dump of struct timespec used by kernel in it's
clock_gettime(2) and clock_settime(2) calls. This file shall not be considered portable.