NTPFROB

Section: NTPsec (8)
Updated: 2021-02-01
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NAME

ntpfrob - frob the clock hardware

SYNOPSIS

ntpfrob [-A] [-b bump] [-a tick] [-p ppsdev] [-c] [-e] [-r] [-?] [-h]

DESCRIPTION

The ntpfrob program frobs the local clock hardware. It collects several small diagnostic functions into a set that will differ depending on your platform and underlying system calls. Portions of it formerly traveled as tickadj and some undocumented small utilities.

COMMAND LINE OPTIONS

-a tick

: Set the kernel variable tick to the value tick specifies.

-A

: Display the kernel variable tick.

-b bump

: Bump the clock by a specified number of microseconds.

-c

: Compute and display clock jitter.

-d

: display values extracted via adjtimex(2).

-D

: display values extracted via adjtimex(2) forcibly including PPS.

-e

: Measure clock precision.

-j

: Generate a report in self-describing JSON.

-p ppsdev

: Look for PPS pulses on a specified device

-r

: Raw mode. Only applies to the jitter mode, and means the raw clock samples should be emitted to stdout for post analysis.

: Print usage and exit.

-h

: Print usage and exit.

-V

: Print the version string and exit.

USAGE

Documentation for some of these functions is scanty; this is a problem inherited from ancient days along with their code. If you suspect you may need to use them, reading the source code may be wise. If you believe you understand the code in more detail than any of these descriptions, please explain it to the NTPsec maintainers.

Normally this tool reports in an eyeball-friendly unstructured text format. With the -j option (where applicable) it reports JSON records. Note that the -j option should be given before any mode option.

The reporting formats of this tool should be considered unstable; they may change as diagnostics are added or improved. JSON reports will be kept forward-compatible through changes.

Clock tick adjustment

The -A function reads your clock's tick rate in microseconds. The -a function sets it. Both rely on the adjtimex(2) system call. This mode finishes by reporting the tick value and (if available) the tick adjustment value.

The -j option applies to this mode.

Tweaking your tick rate is almost never necessary on hardware new enough to have a fully POSIX.1-2001-conformant Unix.

Clock bump

Sometimes it is diagnostically interesting to perturb your clock to watch how ntpd responds and makes corrections. This option does that.

Clock jitter measurement

The -c option can be used to determine the timing jitter due to the operating system in a gettimeofday() call. For most systems, the dominant contribution to the jitter budget is the period of the hardware interrupt, usually in the range between 10 us and 1 ms. For those systems with microsecond counters, the jitter is dominated only by the operating system.

The -j option applies to this mode. With the -r option, write the raw, unsorted clock samples to standard output for post-analysis. All but the last -j or -r option before the -c mode flag is ignored.

Pulse-per-second check

The -p option shows whether the PPS-API (RFC 2783 kernel PPS interface) finds PPS on a specified device.

Measure clock precision

The -e option measure the resolution of the system clock, watching how the current time changes as we read it repeatedly.

The -j option applies to this mode.

EXIT STATUS

One of the following exit values will be returned:

0 (EXIT_SUCCESS)

: Successful program execution.

1 (EXIT_FAILURE)

: The operation failed or the command invocation was not valid.