If ntpd is started with the "-x" flag it means slewing is disabled. This means that it won't use the kernel's frequency adjustment support (via the adjtimex syscall) to manage the time. Instead, it just uses the 'adjtime' call in libc to adjust the clock offset. This has an underlying effect in the kernel of increasing or decreasing the frequency of the clock, but notable does not adjust the 'maxerror' variable inside the kernel. So, the kernel just adds 500us of maxerror once a second, and once that crosses a threshold of 16 sec (after about 8h 53m), the clock gets the "STA_UNSYNC" flag set and crashes Kudu.