1GPSD(8) GPSD Documentation GPSD(8)
2
6 gpsd - interface daemon for GPS receivers
7
9 gpsd [-b] [-D debuglevel] [-F control-socket] [-f framing] [-G] [-h]
10 [-l] [-n] [-N] [-P pidfile] [-r] [-S listener-port] [-s speed]
11 [-V] [[source-name]...]
12
14 If you have a GPS attached on the lowest-numbered USB port of a Linux
15 system, and want to read reports from it on TCP/IP port 2947, it will
16 normally suffice to do this:
17 gpsd /dev/ttyUSB0
19 For the lowest-numbered serial port:
21 gpsd /dev/ttyS0
23 Change the device number as appropriate if you need to use a different
25 port. Command-line flags enable verbose logging, a control port, and
26 other optional extras but should not be needed for basic operation; the
27 one exception, on very badly designed hardware, might be -b (which
28 see).
29 On Linux systems supporting udev, gpsd is normally started
31 automatically when a USB plugin event fires (if it is not already
32 running) and is handed the name of the newly active device. In that
33 case no invocation is required at all.
34 For your initial tests set your GPS hardware to speak NMEA, as gpsd is
36 guaranteed to be able to process that. If your GPS has a native or
37 binary mode with better performance that gpsd knows how to speak, gpsd
38 will autoconfigure that mode.
39 You can verify correct operation by first starting gpsd and then xgps,
41 the X windows test client.
42 If you have problems, the GPSD project maintains a FAQ to assist
44 troubleshooting.
45
47 gpsd is a monitor daemon that collects information from GPSes,
48 differential-GPS radios, or AIS receivers attached to the host machine.
49 Each GPS, DGPS radio, or AIS receiver is expected to be
50 direct-connected to the host via a USB or RS232C serial device. The
51 serial device may be specified to gpsd at startup, or it may be set via
52 a command shipped down a local control socket (e.g. by a USB hotplug
53 script). Given a GPS device by either means, gpsd discovers the correct
54 port speed and protocol for it.
55 gpsd should be able to query any GPS that speaks either the standard
57 textual NMEA 0183 protocol, or the (differing) extended NMEA dialects
58 used by MKT-3301, iTrax, Motorola OnCore, Sony CXD2951, and
59 Ashtech/Thales devices. It can also interpret the binary protocols used
60 by EverMore, Garmin, Navcom, Rockwell/Zodiac, SiRF, Trimble, and u-blox
61 ANTARIS devices. Under Linux it can read NMEA2000 packets through the
62 kernel CAN socket. It can read heading and attitude information from
63 the Oceanserver 5000 or TNT Revolution digital compasses.
64 The GPS reporting formats supported by your instance of gpsd may differ
66 depending on how it was compiled; general-purpose versions support
67 many, but it can be built with protocol subsets down to a singleton for
68 use in constrained environments. For a list of the GPS protocols
69 supported by your instance, see the output of gpsd -l
70 gpsd effectively hides the differences among the GPS types it supports.
72 It also knows about and uses commands that tune these GPSes for lower
73 latency. By using gpsd as an intermediary, applications avoid
74 contention for serial devices.
75 gpsd can use differential-GPS corrections from a DGPS radio or over the
77 net, from a ground station running a DGPSIP server or a Ntrip
78 broadcaster that reports RTCM-104 data; this will shrink position
79 errors by roughly a factor of four. When gpsd opens a serial device
80 emitting RTCM-104, it automatically recognizes this and uses the device
81 as a correction source for all connected GPSes that accept RTCM
82 corrections (this is dependent on the type of the GPS; not all GPSes
83 have the firmware capability to accept RTCM correction packets). See
84 the section called “ACCURACY” and the section called “FILES” for
85 discussion.
86 Client applications will communicate with gpsd via a TCP/IP port, 2947
88 by default). Both IPv4 and IPv6 connections are supported and a client
89 may connect via either.
90 The program accepts the following options:
92 -b
94 Broken-device-safety mode, otherwise known as read-only mode. A few
95 bluetooth and USB receivers lock up or become totally inaccessible
96 when probed or reconfigured; see the hardware compatibility list on
97 the GPSD project website for details. This switch prevents gpsd
98 from writing to a receiver. This means that gpsd cannot configure
99 the receiver for optimal performance, but it also means that gpsd
100 cannot break the receiver. A better solution would be for Bluetooth
101 to not be so fragile. A platform independent method to identify
102 serial-over-Bluetooth devices would also be nice.
103 -D
105 Set debug level. At debug levels 2 and above, gpsd reports incoming
106 sentence and actions to standard error if gpsd is in the foreground
107 (-N) or to syslog if in the background.
108 -F
110 Create a control socket for device addition and removal commands.
111 You must specify a valid pathname on your local filesystem; this
112 will be created as a Unix-domain socket to which you can write
113 commands that edit the daemon's internal device list.
114 -f
116 Fix the framing to the GNSS device. The framing parameter is of the
117 form: [78][ENO][012]. Most GNSS are 8N1. Some Trimble default to
118 8O1. The default is to search for the correct framing.
119 -G
121 This flag causes gpsd to listen on all addresses (INADDR_ANY)
122 rather than just the loop back (INADDR_LOOPBACK) address. For the
123 sake of privacy and security, TPV information is now private to the
124 local machine until the user makes an effort to expose this to the
125 world.
126 -h
128 Display help message and terminate.
129 -l
131 List all drivers compiled into this gpsd instance. The letters to
132 the left of each driver name are the gpsd control commands
133 supported by that driver.
134 -n
136 Don't wait for a client to connect before polling whatever GPS is
137 associated with it. Some RS232 GPSes wait in a standby mode
138 (drawing less power) when the host machine is not asserting DTR,
139 and some cellphone and handheld embedded GPSes have similar
140 behaviors. Accordingly, waiting for a watch request to open the
141 device may save battery power. (This capability is rare in
142 consumer-grade devices). You should use this option if you plan to
143 use gpsd to provide reference clock information to ntpd through a
144 memory-shared segment.
145 -N
147 Don't daemonize; run in foreground. This switch is mainly useful
148 for debugging.
149 -r
151 Use GPS time even with no current fix. Some GPS's have battery
152 powered Real Time Clocks (RTC's) built in, making them a valid time
153 source even before a fix is acquired. This can be useful on a
154 Raspberry Pi, or other device that has no battery powered RTC, and
155 thus has no valid time at startup.
156 -P
158 Specify the name and path to record the daemon's process ID.
159 -S
161 Set TCP/IP port on which to listen for GPSD clients (default is
162 2947).
163 -s
165 Fix the speed to the GNSS device. The default is to autobaud.
166 -V
168 Dump version and exit.
169 Arguments are interpreted as the names of data sources. Normally, a
171 data source is the device pathname of a local device from which the
172 daemon may expect GPS data. But there are three other special source
173 types recognized, for a total of four:
174 Local serial or USB device
176 A normal Unix device name of a serial or USB device to which a
177 sensor is attached. Example: /dev/ttyUSB0.
178 Local PPS device
180 A normal Unix device name of a PPS device to which a PPS source is
181 attached. The device name must start with "/dev/pps" and a local
182 serial or USB GPS device must also be available. Example:
183 /dev/pps0.
184 TCP feed
186 A URI with the prefix "tcp://", followed by a hostname, a colon,
187 and a port number. The daemon will open a socket to the indicated
188 address and port and read data packets from it, which will be
189 interpreted as though they had been issued by a serial device.
190 Example: tcp://data.aishub.net:4006.
191 UDP feed
193 A URI with the prefix "udp://", followed by a hostname, a colon,
194 and a port number. The daemon will open a socket listening for UDP
195 datagrams arriving on the indicated address and port, which will be
196 interpreted as though they had been issued by a serial device.
197 Example: udp://127.0.0.1:5000.
198 Ntrip caster
200 A URI with the prefix "ntrip://" followed by the name of an Ntrip
201 caster (Ntrip is a protocol for broadcasting differential-GPS fixes
202 over the net). For Ntrip services that require authentication, a
203 prefix of the form "username:password@" can be added before the
204 name of the Ntrip broadcaster. For Ntrip service, you must specify
205 which stream to use; the stream is given in the form "/streamname".
206 An example DGPSIP URI could be "dgpsip://dgpsip.example.com" and a
207 Ntrip URI could be
208 "ntrip://foo:bar@ntrip.example.com:80/example-stream". Corrections
209 from the caster will be send to each attached GPS with the
210 capability to accept them.
211 DGPSIP server
213 A URI with the prefix "dgpsip://" followed by a hostname, a colon,
214 and an optional colon-separated port number (defaulting to 2101).
215 The daemon will handshake with the DGPSIP server and read RTCM2
216 correction data from it. Corrections from the server will be set to
217 each attached GPS with the capability to accept them. Example:
218 dgpsip://dgps.wsrcc.com:2101.
219 Remote gpsd feed
221 A URI with the prefix "gpsd://", followed by a hostname and
222 optionally a colon and a port number (if the port is absent the
223 default gpsd port will be used). The daemon will open a socket to
224 the indicated address and port and emulate a gpsd client,
225 collecting JSON reports from the remote gpsd instance that will be
226 passed to local clients.
227 NMEA2000 CAN data
229 A URI with the prefix "nmea2000://", followed by a CAN devicename.
230 Only Linux socket CAN interfaces are supported. The interface must
231 be configured to receive CAN messages before gpsd can be started.
232 If there is more then one unit on the CAN bus that provides GPS
233 data, gpsd chooses the unit from which a GPS message is first seen.
234 Example: nmea2000://can0.
235 (The "ais:://" source type supported in some older versions of the
237 daemon has been retired in favor of the more general "tcp://".)
238 Additionally, two serial device names have a side effect:
240 /dev/ttyAMA0
242 The UART device on a Raspberry Pi. Has the side effect of opening
243 /dev/pps0 for RFC2783 1PPS data.
244 /dev/gpsd0
246 Generic GPS device 0. Has the side effect of opening /dev/pps0 for
247 RFC2783 1PPS data.
248 Note, however, that if /dev/pps0 is the fake "ktimer" PPS, then
250 /dev/pps1 will be used instead.
251 Internally, the daemon maintains a device pool holding the pathnames of
253 devices and remote servers known to the daemon. Initially, this list is
254 the list of device-name arguments specified on the command line. That
255 list may be empty, in which case the daemon will have no devices on its
256 search list until they are added by a control-socket command (see the
257 section called “GPS DEVICE MANAGEMENT” for details on this). Daemon
258 startup will abort with an error if neither any devices nor a control
259 socket are specified.
260 When a device is activated (i.e. a client requests data from it), gpsd
262 attempts to execute a hook from /etc/gpsd/device-hook with first
263 command line argument set to the pathname of the device and the second
264 to ACTIVATE. On deactivation it does the same passing DEACTIVATE for
265 the second argument.
266 gpsd can export data to client applications in three ways: via a
268 sockets interface, via a shared-memory segment, and via D-Bus. The next
269 three major sections describe these interfaces.
270
272 Clients may communicate with the daemon via textual request and
273 responses over a socket. It is a bad idea for applications to speak the
274 protocol directly: rather, they should use the libgps client library
275 and take appropriate care to conditionalize their code on the major and
276 minor protocol version symbols.
277 The request-response protocol for the socket interface is fully
279 documented in gpsd_json(5).
280
282 gpsd has two other (read-only) interfaces.
283 Whenever the daemon recognizes a packet from any attached device, it
285 writes the accumulated state from that device to a shared memory
286 segment. The C and C++ client libraries shipped with GPSD can read this
287 segment. Client methods, and various restrictions associated with the
288 read-only nature of this interface, are documented at libgps(3). The
289 shared-memory interface is intended primarily for embedded deployments
290 in which gpsd monitors a single device, and its principal advantage is
291 that a daemon instance configured with shared memory but without the
292 sockets interface loses a significant amount of runtime weight.
293 The daemon may be configured to emit a D-Bus signal each time an
295 attached device delivers a fix. The signal path is path /org/gpsd, the
296 signal interface is "org.gpsd", and the signal name is "fix". The
297 signal payload layout is as follows:
298 Table 1. Satellite object
300 ┌─────────────────┬────────────────────────────┐
301 │Type │ │
302 │ │ Description │
303 ├─────────────────┼────────────────────────────┤
304 │DBUS_TYPE_DOUBLE │ │
305 │ │ Time (seconds since │
306 │ │ Unix epoch) │
307 ├─────────────────┼────────────────────────────┤
308 │DBUS_TYPE_INT32 │ │
309 │ │ mode │
310 ├─────────────────┼────────────────────────────┤
311 │DBUS_TYPE_DOUBLE │ │
312 │ │ Time uncertainty │
313 │ │ (seconds). │
314 ├─────────────────┼────────────────────────────┤
315 │DBUS_TYPE_DOUBLE │ │
316 │ │ Latitude in │
317 │ │ degrees. │
318 ├─────────────────┼────────────────────────────┤
319 │DBUS_TYPE_DOUBLE │ │
320 │ │ Longitude in │
321 │ │ degrees. │
322 ├─────────────────┼────────────────────────────┤
323 │DBUS_TYPE_DOUBLE │ │
324 │ │ Horizontal │
325 │ │ uncertainty in │
326 │ │ meters, 95% │
327 │ │ confidence. │
328 ├─────────────────┼────────────────────────────┤
329 │DBUS_TYPE_DOUBLE │ │
330 │ │ Altitude in meters. │
331 ├─────────────────┼────────────────────────────┤
332 │DBUS_TYPE_DOUBLE │ │
333 │ │ Altitude │
334 │ │ uncertainty in │
335 │ │ meters, 95% │
336 │ │ confidence. │
337 ├─────────────────┼────────────────────────────┤
338 │DBUS_TYPE_DOUBLE │ │
339 │ │ Course in degrees │
340 │ │ from true north. │
341 ├─────────────────┼────────────────────────────┤
342 │DBUS_TYPE_DOUBLE │ │
343 │ │ Course uncertainty │
344 │ │ in meters, 95% │
345 │ │ confidence. │
346 ├─────────────────┼────────────────────────────┤
347 │DBUS_TYPE_DOUBLE │ │
348 │ │ Speed, meters per │
349 │ │ second. │
350 ├─────────────────┼────────────────────────────┤
351 │DBUS_TYPE_DOUBLE │ │
352 │ │ Speed uncertainty │
353 │ │ in meters per │
354 │ │ second, 95% │
355 │ │ confidence. │
356 ├─────────────────┼────────────────────────────┤
357 │DBUS_TYPE_DOUBLE │ │
358 │ │ Climb, meters per │
359 │ │ second. │
360 ├─────────────────┼────────────────────────────┤
361 │DBUS_TYPE_DOUBLE │ │
362 │ │ Climb uncertainty │
363 │ │ in meters per │
364 │ │ second, 95% │
365 │ │ confidence. │
366 ├─────────────────┼────────────────────────────┤
367 │DBUS_TYPE_STRING │ │
368 │ │ Device name │
369 └─────────────────┴────────────────────────────┘
370
372 gpsd maintains an internal list of GPS devices (the "device pool"). If
373 you specify devices on the command line, the list is initialized with
374 those pathnames; otherwise the list starts empty. Commands to add and
375 remove GPS device paths from the daemon's device list must be written
376 to a local Unix-domain socket which will be accessible only to programs
377 running as root. This control socket will be located wherever the -F
378 option specifies it.
379 A device may will also be dropped from the pool if GPSD gets a zero
381 length read from it. This end-of-file condition indicates that the
382 device has been disconnected.
383 When gpsd is properly installed along with hotplug notifier scripts
385 feeding it device-add commands over the control socket, gpsd should
386 require no configuration or user action to find devices.
387 Sending SIGHUP to a running gpsd forces it to close all GPSes and all
389 client connections. It will then attempt to reconnect to any GPSes on
390 its device list and resume listening for client connections. This may
391 be useful if your GPS enters a wedged or confused state but can be
392 soft-reset by pulling down DTR.
393 When gpsd is called with no initial devices (thus, expecting devices to
395 be passed to it by notifications to the control socket), and reaches a
396 state where there are no devices connected and no subscribers after
397 after some devices have been seen, it shuts down gracefully. It is
398 expected that future device hotplug events will reactivate it.
399 To point gpsd at a device that may be a GPS, write to the control
401 socket a plus sign ('+') followed by the device name followed by LF or
402 CR-LF. Thus, to point the daemon at /dev/foo. send "+/dev/foo\n". To
403 tell the daemon that a device has been disconnected and is no longer
404 available, send a minus sign ('-') followed by the device name followed
405 by LF or CR-LF. Thus, to remove /dev/foo from the search list, send
406 "-/dev/foo\n".
407 To send a control string to a specified device, write to the control
409 socket a '!', followed by the device name, followed by '=', followed by
410 the control string.
411 To send a binary control string to a specified device, write to the
413 control socket a '&', followed by the device name, followed by '=',
414 followed by the control string in paired hex digits.
415 Your client may await a response, which will be a line beginning with
417 either "OK" or "ERROR". An ERROR response to an add command means the
418 device did not emit data recognizable as GPS packets; an ERROR response
419 to a remove command means the specified device was not in gpsd's device
420 pool. An ERROR response to a ! command means the daemon did not
421 recognize the devicename specified.
422 The control socket is intended for use by hotplug scripts and other
424 device-discovery services. This control channel is separate from the
425 public gpsd service port, and only locally accessible, in order to
426 prevent remote denial-of-service and spoofing attacks.
427
429 The base User Estimated Range Error (UERE) of GPSes is 8 meters or less
430 at 66% confidence, 15 meters or less at 95% confidence. Actual
431 horizontal error will be UERE times a dilution factor dependent on
432 current satellite position. Altitude determination is more sensitive to
433 variability in ionospheric signal lag than latitude/longitude is, and
434 is also subject to errors in the estimation of local mean sea level;
435 base error is 12 meters at 66% confidence, 23 meters at 95% confidence.
436 Again, this will be multiplied by a vertical dilution of precision
437 (VDOP) dependent on satellite geometry, and VDOP is typically larger
438 than HDOP. Users should not rely on GPS altitude for life-critical
439 tasks such as landing an airplane.
440 These errors are intrinsic to the design and physics of the GPS system.
442 gpsd does its internal computations at sufficient accuracy that it will
443 add no measurable position error of its own.
444 DGPS correction will reduce UERE by a factor of 4, provided you are
446 within about 100mi (160km) of a DGPS ground station from which you are
447 receiving corrections.
448 On a 4800bps connection, the time latency of fixes provided by gpsd
450 will be one second or less 95% of the time. Most of this lag is due to
451 the fact that GPSes normally emit fixes once per second, thus expected
452 latency is 0.5sec. On the personal-computer hardware available in 2005
453 and later, computation lag induced by gpsd will be negligible, on the
454 order of a millisecond. Nevertheless, latency can introduce significant
455 errors for vehicles in motion; at 50km/h (31mi/h) of speed over ground,
456 1 second of lag corresponds to 13.8 meters change in position between
457 updates.
458 The time reporting of the GPS system itself has an intrinsic accuracy
460 limit of 14 nanoseconds, but this can only be approximated by
461 specialized receivers using that send the high-accuracy PPS
462 (Pulse-Per-Second) over RS232 to cue a clock crystal. Most GPS
463 receivers only report time to a precision of 0.01s or 0.001s, and with
464 no accuracy guarantees below 1sec.
465 If your GPS uses a SiRF chipset at firmware level 231, reported UTC
467 time may be off by the difference between whatever default leap-second
468 offset has been compiled in and whatever leap-second correction is
469 currently applicable, from startup until complete subframe information
470 is received. Firmware levels 232 and up don't have this problem. You
471 may run gpsd at debug level 4 to see the chipset type and firmware
472 revision level.
473 There are exactly two circumstances under which gpsd relies on the
475 host-system clock:
476 In the GPS broadcast signal, GPS time is represented using a week
478 number that rolls over after 2^10 or 2^13 weeks (about 19.6 years, or
479 157 years), depending on the spacecraft. Receivers are required to
480 disambiguate this to the correct date, but may have difficulty due to
481 not knowing time to within half this interval, or may have bugs. Users
482 have reported incorrect dates which appear to be due to this issue.
483 gpsd uses the startup time of the daemon detect and compensate for
484 rollovers while it is running, but otherwise reports the date as it is
485 reported by the receiver without attempting to correct it.
486 If you are using an NMEA-only GPS (that is, not using SiRF or Garmin or
488 Zodiac binary mode), gpsd relies on the system clock to tell it the
489 current century. If the system clock returns an invalid value near
490 zero, and the GPS does not emit GPZDA at the start of its update cycle
491 (which most consumer-grade NMEA GPSes do not) then the century part of
492 the dates gpsd delivers may be wrong. Additionally, near the century
493 turnover, a range of dates as wide in seconds as the accuracy of your
494 system clock may be referred to the wrong century.
495
497 gpsd can provide reference clock information to ntpd, to keep the
498 system clock synchronized to the time provided by the GPS receiver.
499 On Linux, gpsd includes support for interpreting the PPS pulses emitted
501 at the start of every clock second on the carrier-detect lines of some
502 serial GPSes; this pulse can be used to update NTP at much higher
503 accuracy than message time provides. You can determine whether your GPS
504 emits this pulse by running at -D 5 and watching for carrier-detect
505 state change messages in the logfile. In addition, if your kernel
506 provides the RFC 2783 kernel PPS API then gpsd will use that for extra
507 accuracy.
508 Detailed instructions for using GPSD to set up a high-quality time
510 service can be found among the documentation on the GPSD website.
511
513 On operating systems that support D-BUS, gpsd can be built to broadcast
514 GPS fixes to D-BUS-aware applications. As D-BUS is still at a pre-1.0
515 stage, we will not attempt to document this interface here. Read the
516 gpsd source code to learn more.
517
519 gpsd, if given the -G flag, will listen for connections from any
520 reachable host, and then disclose the current position. Before using
521 the -G flag, consider whether you consider your computer's location to
522 be sensitive data to be kept private or something that you wish to
523 publish.
524 gpsd must start up as root in order to open the NTPD shared-memory
526 segment, open its logfile, and create its local control socket. Before
527 doing any processing of GPS data, it tries to drop root privileges by
528 setting its UID to "nobody" (or another configured userid) and its
529 group ID to the group of the initial GPS passed on the command line —
530 or, if that device doesn't exist, to the group of /dev/ttyS0.
531 Privilege-dropping is a hedge against the possibility that carefully
533 crafted data, either presented from a client socket or from a subverted
534 serial device posing as a GPS, could be used to induce misbehavior in
535 the internals of gpsd. It ensures that any such compromises cannot be
536 used for privilege elevation to root.
537 The assumption behind gpsd's particular behavior is that all the tty
539 devices to which a GPS might be connected are owned by the same
540 non-root group and allow group read/write, though the group may vary
541 because of distribution-specific or local administrative practice. If
542 this assumption is false, gpsd may not be able to open GPS devices in
543 order to read them (such failures will be logged).
544 In order to fend off inadvertent denial-of-service attacks by port
546 scanners (not to mention deliberate ones), gpsd will time out inactive
547 client connections. Before the client has issued a command that
548 requests a channel assignment, a short timeout (60 seconds) applies.
549 There is no timeout for clients in watcher or raw modes; rather, gpsd
550 drops these clients if they fail to read data long enough for the
551 outbound socket write buffer to fill. Clients with an assigned device
552 in polling mode are subject to a longer timeout (15 minutes).
553
555 If multiple NMEA talkers are feeding RMC, GLL, and GGA sentences to the
556 same serial device (possible with an RS422 adapter hooked up to some
557 marine-navigation systems), a 'TPV' response may mix an altitude from
558 one device's GGA with latitude/longitude from another's RMC/GLL after
559 the second sentence has arrived.
560 gpsd may change control settings on your GPS (such as the emission
562 frequency of various sentences or packets) and not restore the original
563 settings on exit. This is a result of inadequacies in NMEA and the
564 vendor binary GPS protocols, which often do not give clients any way to
565 query the values of control settings in order to be able to restore
566 them later.
567 When using SiRF chips, the VDOP/TDOP/GDOP figures and associated error
569 estimates are computed by gpsd rather than reported by the chip. The
570 computation does not exactly match what SiRF chips do internally, which
571 includes some satellite weighting using parameters gpsd cannot see.
572 Autobauding on the Trimble GPSes can take as long as 5 seconds if the
574 device speed is not matched to the GPS speed.
575 Generation of position error estimates (eph, epv, epd, eps, epc) from
577 the incomplete data handed back by GPS reporting protocols involves
578 both a lot of mathematical black art and fragile device-dependent
579 assumptions. This code has been bug-prone in tbe past and problems may
580 still lurk there.
581 AIDVM decoding of types 16-17, 22-23, and 25-26 is unverified.
583 GPSD presently fully recognizes only the 2.1 level of RTCM2 (message
585 types 1, 3, 4, 5, 6, 7, 9, 16). The 2.3 message types 13, 14, and 31
586 are recognized and reported. Message types 8, 10-12, 15-27, 28-30
587 (undefined), 31-37, 38-58 (undefined), and 60-63 are not yet supported.
588 The ISGPS used for RTCM2 and subframes decoder logic is sufficiently
590 convoluted to confuse some compiler optimizers, notably in GCC 3.x at
591 -O2, into generating bad code.
592 Devices meant to use PPS for high-precision timekeeping may fail if
594 they are specified after startup by a control-socket command, as
595 opposed to on the daemon's original command line. Root privileges are
596 dropped early, and some Unix variants require them in order to set the
597 PPS line discipline. Under Linux the POSIX capability to set the line
598 discipline is retained, but other platforms cannot use this code.
599 USB GPS devices often do not identify themselves through the USB
601 subsystem; they typically present as the class 00h (undefined) or class
602 FFh (vendor-specific) of USB-to-serial adapters. Because of this, the
603 Linux hotplug scripts must tell gpsd to sniff data from every
604 USB-to-serial adapter that goes active and is known to be of a type
605 used in GPSes. No such device is sent configuration strings until after
606 it has been identified as a GPS, and gpsd never opens a device that is
607 opened by another process. But there is a tiny window for non-GPS
608 devices not opened; if the application that wants them loses a race
609 with GPSD its device open will fail and have to be retried after GPSD
610 sniffs the device (normally less than a second later).
611
613 /dev/ttyS0
614 Prototype TTY device. After startup, gpsd sets its group ID to the
615 owning group of this device if no GPS device was specified on the
616 command line does not exist.
617 /etc/gpsd/device-hook
619 Optional file containing the device activation/deactivation script.
620 Note that while /etc/gpsd is the default system configuration
621 directory, it is possible to build the GPSD source code with
622 different assumptions. See above for further details on the
623 device-hook mechanism.
624
626 By setting the environment variable GPSD_SHM_KEY, you can control the
627 key value used to create the shared-memory segment used for
628 communication with the client library. This will be useful mainly when
629 isolating test instances of gpsd from production ones.
630
632 The official NMEA protocol standards for NMEA0183 and NMEA2000 are
633 available from the National Marine Electronics Association, but are
634 proprietary and expensive; the maintainers of gpsd have made a point of
635 not looking at them. The GPSD project website links to several
636 documents that collect publicly disclosed information about the
637 protocol.
638 gpsd parses the following NMEA sentences: RMC, GGA, GLL, GSA, GSV, VTG,
640 ZDA, GBS, HDT, DBT, GST. It recognizes these with either the normal GP
641 talker-ID prefix, or with the GN prefix used by GLONASS, or with the II
642 prefix emitted by Seahawk Autohelm marine navigation systems, or with
643 the IN prefix emitted by some Garmin units, or with the EC prefix
644 emitted by ECDIS units, or with the SD prefix emitted by depth
645 sounders, or with the HC and TI prefix emitted by some Airmar
646 equipment. It recognizes some vendor extensions: the PGRME emitted by
647 some Garmin GPS models, the OHPR emitted by Oceanserver digital
648 compasses, the PTNTHTM emitted by True North digital compasses, the
649 PMTK omitted by some San Jose Navigation GPSes, and the PASHR sentences
650 emitted by some Ashtech GPSes.
651 Note that gpsd JSON returns pure decimal degrees, not the hybrid
653 degree/minute format described in the NMEA standard.
654 Differential-GPS corrections are conveyed by the RTCM protocols. The
656 applicable standard for RTCM-104 V2 is RTCM Recommended Standards for
657 Differential GNSS (Global Navigation Satellite) Service RTCM Paper
658 136-2001/SC 104-STD. The applicable standard for RTCM-104 V3 is RTCM
659 Standard 10403.1 for Differential GNSS Services - Version 3 RTCM Paper
660 177-2006-SC104-STD. Ordering instructions for the RTCM standards are
661 accessible from the website of the Radio Technical Commission for
662 Maritime Services under "Publications".
663 AIS is defined by ITU Recommendation M.1371, Technical Characteristics
665 for a Universal Shipborne Automatic Identification System Using Time
666 Division Multiple Access. The AIVDM/AIVDO format understood by this
667 program is defined by IEC-PAS 61162-100, Maritime navigation and
668 radiocommunication equipment and systems. A more accessible description
669 of both can be found at AIVDM/AIVDO Protocol Decoding, on the
670 references page of the GPSD project website.
671 Subframe data is defined by IS-GPS-200E, GLOBAL POSITIONING SYSTEM WING
673 (GPSW) SYSTEMS ENGINEERING & INTEGRATION, INTERFACE SPECIFICATION
674 IS-GPS-200 Revision E. The format understood by this program is defined
675 in Section 20 (Appendix II) of the IS-GPS-200E, GPS NAVIGATION DATA
676 STRUCTURE FOR DATA, D(t)
677 JSON is specified by RFC 7159, The JavaScript Object Notation (JSON)
679 Data Interchange Format.
680 The API for PPS time service is specified by RFC 2783, Pulse-Per-Second
682 API for UNIX-like Operating Systems, Version 1.0
683
685 gpsdctl(8), gps(1), libgps(3), gpsd_json(5), libgpsmm(3), gpsprof(1),
686 gpsfake(1), gpsctl(1), gpscat(1),
687
689 Authors: Eric S. Raymond, Chris Kuethe, Gary Miller. Former authors
690 whose bits have been plowed under by code turnover: Remco Treffcorn,
691 Derrick Brashear, Russ Nelson. This manual page by Eric S. Raymond
692 <esr@thyrsus.com>.
693The GPSD Project 9 Aug 2004 GPSD(8)