On Tue Jul 11 09:30:12 2017, kunschikov@gmail.com wrote:
>       We are using CentOS as base system and can't switch to BSD.

=> I said BSDs because it was invented for 4.3 BSD in 1993
(and I used this system at that time). Note adjtime() is supported
by Linux too (cd http://man7.org/linux/man-pages/man3/adjtime.3.html)

> I am not
> sure which signal can be sent to the dhclient in order to recalculate
> sleep/wake timestamps. Select can be canceled on signal reception but after
> that dhclient is going to sleep again till the next date, which is
> calculated not from current time, but from the scheduled one.

=> you can send a signal to the process (but avoid to kill it).
select takes a relative time so if you are lucky it is recomputed
with the "new" current time.

> I am solving this problem by replacing gettimeofday() with
> clock_gettime(CLOCK_MONOTONIC_RAW,..) for dhclient. LD_PRELOAD with
> gettimofday()# replacement library does the trick.  #Proper solution will
> require modification of the dhclient scheduler.

=> you solution deals with the problem at its root (not increasing
gettimeofday). I am not sure it is correct to modify the scheduler:
the assumption the current time is increasing is not so crazy...

> Thanks for quick reply.

=> can we close the ticket?