---
name: "ppscheck"
section: "8"
platform: "linux"
package: "gpsd"
version: "3.27.5-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/ppscheck"
---

# ppscheck(8)

tool to check a serial port for PPS

## NAME

ppscheck - tool to check a serial port for PPS

## SYNOPSIS

**ppscheck** \[-?\] \[--help\] \[-p\] \[--pps\] \[--version\] \[-h\] \[-V\]

**ppscheck** \[-m\] device

## DESCRIPTION

**ppscheck** watches a specified serial port for transitions that might be PPS. It looks for changes in handshake lines CD, CTS, DSR, and RI by running ioctl(...., TIOCMIWAIT, ...) in a loop. When it sees a state change it emits a timestamped line of output dumping the state of the handshake signals. It’s useful for checking whether a device is emitting PPS.

**ppscheck** can run as a normal user, but that user must have permissions to read the target device.  Running under **sudo** may, or may not, work. Running as root will always work.

To check the first serial port do this:

```
# ppscheck /dev/ttyS0
```

As a side effect, **ppscheck** will try to create the matching /dev/ppsX by setting the tty line discipline (ldisc) to N\_PPS (18).  You should then have a device /dev/pps0.  Note that not all serial devices support ldisc N\_PPS.

You can now use **ppscheck** to see if the KPPS (RFC 2783) interface is working:

```
# ppscheck /dev/pps0
```

**ppscheck** is not intended for routine use, but rather for diagnostic purposes. Once you have verified a particular device can output PPS signals you will never need to use it again on that device.

## OPTIONS

The program accepts the following options:

``-?, `-h, `--help``

Print help message, then exit.

``-m, `--match``

Find PPS device that matches *device*.

``-p, `--pps``

Print active PPS devices, then exit.

``-V, `--version``

Dump version, then exit.

- **-x SEC**`, `**--seconds SEC**

  **Exit after delay of SEC seconds.**

## ARGUMENTS

**The** *device* **argument should be the pathname of a device. Such as** **/dev/ttyS0 or /dev/pps0. It will be the device monitored.**

**For a tty device, each output line is the second and nanosecond parts** **of a timestamp followed by the names of the handshake signals then** **asserted. Off transitions may generate lines with no signals asserted.**

**For a pps device, each output line will contain the assert and clear** **times last detected by KPPS.**

**If you don’t see output within a second, use cgps, xgps, or some** **other equivalent tool to check that your device has a satellite lock and** **is getting 3D fixes before giving up on the possibility of PPS.**

**Check your cable. Cheap DB9 to DB9 cables such as those issued with** **UPSes often carry TXD/RXD/GND only, omitting handshake lines such as** **CD. Suspect this especially if the cable jacket looks too skinny to** **hold more than three leads!**

**Most GPS that have built in USB do not support PPS. When in doubt,** **contact the vendor for confirmation that your device does supply PPS.**

## RETURN VALUES

**0**

**OK**

**1**

**if the device could not be opened, or some other failure**

## SEE ALSO

**[cgps(1)](/cgps/1.md), [xgps(1)](/xgps/1.md), [gpsd(8)](/gpsd/8.md)**

## RESOURCES

**Project web site:**  **\<https://gpsd.io/\>**

## COPYING

**This file is Copyright 2013 by the GPSD project**\
 **SPDX-License-Identifier: BSD-2-clause**

## AUTHOR

**Eric S. Raymond**