I think ntpd crashes are because my server lost time. I have ntpd in two server, now I've seen that in one of these ntp crashes and the time of the server is 1 hour forward. That's why ntp crashes: server time goes 1 hour forward and ntp can't resynchronize so it crashes. Now I don't know why my server time goes 1 hour forward. Hwclock --debug says that the time is correct, it is set on UTC, so why sometimes it goes forward? Perhaps a problem in the cmos battery?