17.1 Adjtimex
HISTORIC
The adjtimex command can be used to counter systematic drift in the system clock. It is tricky to fine tune, and it is recommended that you use the network time protocol (Section 17.6) instead.
The command communicates with the kernel to change the number of ticks
in a day (default is 10000 which corresponds to about 8.64 seconds per
tick) and the frequency (default is 0) of the system clock. In Debian
you can use the command adjtimexconfig to automatically
tune the tick and frequency to match the accuracy of the hardware
clock (assumed to be accurate) and so that the change has effect on
each boot. Alternatively, override the automatic settings by editting
/etc/adjtimex.conf.
I a system where the system clock was losing (very) roughly 1 second per hour. (The hardware clock seemed to lose nearly one second each day.) Not too much on the face of it but considering the machine is rarely rebooted this can become a significant drift. For this machine a tick of 10002 and a frequency of 4000000 set the clock accurately:
On an old 486/DX66 the system clock was gaining about 22 seconds in 24 hours and the hardware clock gaining about 10 seconds in 24 hours. Removing 3 ticks had the dramatic effect of making the system clock pretty accurate.
On yet another computer the system clock was losing about 1 second every hour (16 seconds in 24 hours). Running adjtimexconfig:
should adjust the ticks for the system clock against the hardware
clock which is assumed to be, and generally is, accurate. However,
after 24 hours the system clock was still about 5 seconds slow. The
hwclock was also a few seconds out after a weekend. The parameters in
/etc/adjtimex.conf were:
TICK=10000
FREQ=1653461At 1pm one day the clocks were reset with adjustment:
See how it goes. If it works then update /Path{/etc/adjtimex.conf} to match this.
At 4pm the following day the clock was 10 seconds slow. So reset the clock and try:
Today we avoid all this fidling around by using the network time protocol (NTP) as explained in Section 17.6.
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