What's the easiest way to make Busybox keep correct time?

[Harald Becker]

Hi Denys!

On 02.09.2014 15:52, Denys Vlasenko wrote:
> $ busybox ntpd --help
> BusyBox v1.22.1 (2014-02-01 19:25:19 CET) multi-call binary.
>
> Usage: ntpd [-dnqNwl] [-S PROG] [-p PEER]...
>
> NTP client/server
>
>      -d    Verbose
>      -n    Do not daemonize
>      -q    Quit after clock is set
>      -N    Run at high priority
>      -w    Do not set time (only query peers), implies -n
>      -l    Run as server on port 123
>      -p PEER    Obtain time from PEER (may be repeated)
>      -S PROG    Run PROG after stepping time, stratum change, and every 11 mins
> ^^^^^^^^^^^^^^^^^^
>      use this to periodically set the hw clock

What about this (from hwclock manpage)?

Automatic Hardware Clock Synchronization By the Kernel

You should be aware of another way that the Hardware Clock is kept 
synchronized in some systems. The Linux kernel has a mode wherein it 
copies the System Time to the Hardware Clock every 11 minutes. This is a 
good mode to use when you are using something sophisticated like ntp to 
keep your System Time synchronized. (ntp is a way to keep your System 
Time synchronized either to a time server somewhere on the network or to 
a radio clock hooked up to your system. See RFC 1305).

This mode (we'll call it "11 minute mode") is off until something turns 
it on. The ntp daemon xntpd is one thing that turns it on. You can turn 
it off by running anything, including hwclock --hctosys, that sets the 
System Time the old fashioned way.

To see if it is on or off, use the command adjtimex --print and look at 
the value of "status". If the "64" bit of this number (expressed in 
binary) equal to 0, 11 minute mode is on. Otherwise, it is off.

If your system runs with 11 minute mode on, don't use hwclock --adjust 
or hwclock --hctosys. You'll just make a mess. It is acceptable to use a 
hwclock --hctosys at startup time to get a reasonable System Time until 
your system is able to set the System Time from the external source and 
start 11 minute mode.


The question is: Does Busybox ntpd activate this 11 minute mode?

--
Harald