gpsd (GPS Daemon)

gpsd is a service daemon that reads data from GPS/GNSS receivers and makes it available to multiple clients over a local socket. Applications such as Chrony (NTP), navigation software, and location-aware tools query gpsd rather than the device directly, allowing multiple programs to share a single GPS receiver simultaneously.

gpsd is pre-installed on Shani OS. Not active by default — enable it when a GPS receiver is connected.

---

Supported Hardware

gpsd works with virtually any GPS receiver that presents as a serial device:

• USB GPS dongles — appear as /dev/ttyUSB0 or /dev/ttyACM0
• Serial GPS modules — appear as /dev/ttyS0 or /dev/ttyAMA0
• NMEA-over-Bluetooth — appear as /dev/rfcomm0

Identify your device after plugging it in:

# USB devices
lsusb

# New serial devices (watch for new entries after plugging in)
ls /dev/tty{USB,ACM}*

# Check kernel messages for the assigned device node
dmesg | tail -20

---

Enable & Configure

Specify the Device

Edit /etc/default/gpsd (or /etc/gpsd depending on packaging):

# Device the GPS receiver is connected to
DEVICES="/dev/ttyUSB0"

# Options passed to gpsd
GPSD_OPTIONS="-n"    # -n: don't wait for a client to poll — start reading immediately

# Start gpsd on boot
START_DAEMON="true"

sudo systemctl enable --now gpsd
systemctl status gpsd

Socket Activation (Default)

gpsd on Arch uses socket activation — it starts on demand when a client connects. Enable the socket unit instead:

sudo systemctl enable --now gpsd.socket

---

Status & Testing

# Interactive GPS monitor — shows satellite view, fix status, lat/lon/alt
gpsd -N -D 2 /dev/ttyUSB0   # run in foreground for testing

# cgps — ncurses client showing position and satellite data
cgps -s

# gpsmon — lower-level protocol monitor
gpsmon

# Raw NMEA sentences from the device
cat /dev/ttyUSB0

cgps output key fields:

| Field | Meaning | |-------|---------| | Status | NO FIX / 2D FIX / 3D FIX | | Latitude / Longitude | Position in decimal degrees | | Altitude | Height above sea level | | Speed | Ground speed | | Satellites Used | Number of satellites contributing to the fix |

A 3D fix requires at least 4 satellites. Getting a first fix (TTFF) outdoors typically takes 30–90 seconds on a cold start.

---

Using GPS as a Time Source (Chrony)

A GPS receiver provides highly accurate time via the PPS (Pulse Per Second) signal. Pair gpsd with Chrony to use GPS as an NTP reference:

# /etc/chrony.conf — add these lines
refclock SHM 0 offset 0.5 delay 0.2 refid GPS
refclock SOCK /var/run/chrony.ttyUSB0.sock refid PPS

sudo systemctl restart chronyd
chronyc sources -v   # GPS should appear as a source

PPS requires hardware support from the GPS module. Most consumer USB GPS dongles do not expose PPS — check your hardware specs.

---

Firewall

gpsd listens on localhost:2947 by default. If you need LAN access (e.g., to share one GPS across multiple machines):

# Edit /etc/default/gpsd and add -G to listen on all interfaces:
GPSD_OPTIONS="-n -G"

sudo firewall-cmd --add-port=2947/tcp --permanent
sudo firewall-cmd --reload

---

Troubleshooting

| Issue | Solution | |-------|----------| | cgps shows NO FIX | Move outdoors — GPS requires clear sky view; cold start takes up to 90 seconds | | Device not found | Check ls /dev/ttyUSB*; add your user to the uucp group for non-root access: sudo usermod -aG uucp $USER | | gpsd not reading device | Try running in foreground: sudo gpsd -N -D 5 /dev/ttyUSB0 — look for permission or baud rate errors | | ModemManager interfering | ModemManager probes serial devices and can disrupt GPS. Add a udev rule to ignore it: sudo tee /etc/udev/rules.d/99-gpsd.rules <<< 'ATTRS{idVendor}=="XXXX", ATTRS{idProduct}=="YYYY", ENV{ID_MM_DEVICE_IGNORE}="1"' (replace with your device's IDs from lsusb) | | Multiple clients can't connect | gpsd handles multiple clients natively — no configuration needed; verify gpsd is running with systemctl status gpsd |