hwclock with alpine on macOS

[nobeh]

I am having issues with default alpine image when trying to use hwclock:

$ docker run --rm --privileged -it alpine /bin/sh

with kernel messages:

# dmesg | grep clock
[    0.000000] clocksource: arch_sys_counter: mask: 0xffffffffffffff max_cycles: 0x588fe9dc0, max_idle_ns: 440795202592 ns
[    0.000000] sched_clock: 56 bits at 24MHz, resolution 41ns, wraps every 4398046511097ns
[    0.025177] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275000 ns
[    0.030039] PTP clock support registered
[    0.038209] clocksource: Switched to clocksource arch_sys_counter
[    0.073485] rtc-pl031 40002000.rtc: setting system clock to 2025-01-16T10:17:43 UTC (1737022663)
[    0.144051] clk: Disabling unused clocks

which leads to failing hwclock:

# hwclock -s
hwclock: can't open '/dev/misc/rtc': No such file or directory

because it seems that there's no RTC set for the image:

# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
arch_sys_counter
/ # cat /sys/devices/system/clocksource/clocksource0/available_clocksource
arch_sys_counter

and there is not RTC in /dev:

# ls /dev/
autofs         fuse           loop2          nbd3           random         ublk-control   vdc
binder         hwbinder       loop3          net            shm            urandom        vhost-net
btrfs-control  kmsg           mqueue         null           stderr         userfaultfd    vhost-vsock
console        loop-control   nbd0           ppp            stdin          vda            vndbinder
fd             loop0          nbd1           ptmx           stdout         vdb            zero
full           loop1          nbd2           pts            tty            vdb1           zram0

My setup:

$  docker info
...
  Kernel Version: 6.12.9-orbstack-00297-gaa9b46293ea3
 Operating System: OrbStack
 OSType: linux
 Architecture: aarch64
 CPUs: 10
 Total Memory: 15.66GiB
 Name: orbstack

🐞 ? This work in Docker but not with OrbStack. Anyone might have had similar issues?

[nobeh]

Why and the context?

To ensure the clock sync on MacOS -- docker/for-mac#2076 (comment)

[kdrag0n]

We don't use RTC. OrbStack always keeps the clock synced.