GPSFAKE(1)		      GPSD Documentation		    GPSFAKE(1)

NAME
       gpsfake - test harness for gpsd, simulating a GNSS receiver

SYNOPSIS
       gpsfake [OPTIONS] infile

       gpsfake -h

       gpsfake -V

DESCRIPTION
       gpsfake is a test harness for gpsd and its clients. It opens a pty
       (pseudo-TTY), launches a gpsd instance that thinks the slave side of
       the pty is its GNSS device, and repeatedly feeds the contents of one or
       more test logfiles through the master side to the GNSS receiver. If
       there are multiple logfiles, sentences from them are interleaved in the
       order the files are specified.

       gpsfake does not require root privileges, but will run fine as root.
       It can be run concurrently with a production gpsd instance without
       causing problems, as long as you use the -P option.  Running under sudo
       will cause minor loss of functionality.

       The logfiles may contain packets in any supported format, including in
       particular NMEA, SiRF, TSIP, or Zodiac. Leading lines beginning with #
       will be treated as comments and ignored, except in the following
       special cases.

       These are interpreted directly by gpsfake:

       •   a comment of the form #Serial: [0-9] [78][NOE][12] may be used to
	   set serial parameters for the log - baud rate, word length, stop
	   bits.

       •   a comment of the form #Transport: UDP may be used to fake a UDP
	   source rather than the normal pty.

       •   a comment of the form #Transport: TCP may be used to fake a TCP
	   source rather than the normal pty.

       These are interpreted directly by gpsd:

       •   a comment of the form # Date: yyyy-mm-dd (ISO8601 date format) may
	   be used to set the initial date for the log.

       The gpsd instance is run in foreground. The thread sending fake GNSS
       data to the daemon is run in background.

OPTIONS
       -?, -h, --help
	   Print a usage message and exit.

       -1, --singleshot
	   The logfile is interpreted once only rather than repeatedly. This
	   option is intended to facilitate regression testing.

       -b, --baton
	   Enable a twirling-baton progress indicator on standard error. At
	   termination, it reports elapsed time.

       -c COUNT, --cycle COUNT
	   Sets the delay between sentences in seconds. Fractional values of
	   seconds are legal. The default is zero (no delay).

       -d LVL, --debug LVL
	   Pass a -D option to the daemon: thus -D 4 is shorthand for -o="-D
	   4".

       -g, -G, --gdb, --lldb
	   Use the monitor facility to run the gpsd instance within gpsfake
	   under control of gdb or lldb, respectively. They also disable the
	   timeout on daemon inactivity, to allow for breakpointing. If
	   necessary, the timeout can be reenabled by a subsequent -W or
	   --wait . If xterm and $DISPLAY are available, these options launch
	   the debugger in a separate xterm window, to separate the debugger
	   dialog from the program output, but otherwise run it directly. In
	   the gdb case, -tui is used with xterm but not otherwise, since
	   curses and program output don’t play nicely together. Although lldb
	   lacks an equivalent option, some versions have a 'gui' command.

       -i, --promptme
	   Single-step through logfiles. It dumps the line or packet number
	   (and the sentence if the protocol is textual) followed by "? ".
	   Only when the user keys Enter is the line actually fed to gpsd.

       -l, --linedump
	   Print a line or packet number just before each sentence is fed to
	   the daemon. If the sentence is textual (e.g. NMEA), the text is
	   printed as well. If not, the packet will be printed in hexadecimal
	   (except for RTCM packets, which aren’t dumped at all). This option
	   is useful for checking that gpsfake is getting packet boundaries
	   right.

       -m PROG, --monitor PROG
	   Specify a monitor program (PROG) inside which the daemon should be
	   run. This option is intended to be used with valgrind(1) , gdb(1)
	   and similar programs.

       -n, --nowait
	   Pass -n to the daemon to start the daemon reading the GNSS receiver
	   without waiting for a client (equivalent to -o="-n").

       -o="OPTS", --option="OPTS"
	   Specify options to pass to the daemon. The equal sign (=) and
	   quotes are required so that gpsd options are not confused with
	   gpsfake options. To start the daemon reading the GNSS receiver
	   without waiting for a client use -o="-n" (equivalent to the -n)
	   which passes -n to the gpsd daemon. The option -o="-D 4" passes a
	   -D 4 to the daemon, equivalent to the using -D 4.

       -p, --pipe
	   Sets watcher mode and dump the NMEA and GPSD notifications
	   generated by the log to standard output. This is useful for
	   regression testing.

       -P PORT, --port PORT
	   Sets the daemon’s listening port to PORT.

       -q, --quiet
	   Tell gpsfake to suppress normal progress output and thus act in a
	   quiet manner.

       -r STR, --clientinit STR
	   Specify an initialization command to use in pipe mode. The default
	   is ?WATCH={"enable":true,"json":true}.

       -s SPEED, --speed SPEED
	   Sets the baud rate for the slave tty. The default is 4800.

       -S, --slow
	   Tells gpsfake to insert realistic delays in the test input rather
	   than trying to stuff it through the daemon as fast as possible.
	   This will make the test(s) run much slower, but avoids flaky
	   failures due to machine load and possible race conditions in the
	   pty layer.

       -t, --tcp
	   Forces the test framework to use TCP rather than pty devices.
	   Besides being a test of TCP source handling, this may be useful for
	   testing from within chroot jails where access to pty devices is
	   locked out.

       -T, --sysinfo
	   Makes gpsfake print some system information and then exit.

       -u, --udp
	   Forces the test framework to use UDP rather than pty devices.
	   Besides being a test of UDP source handling, this may be useful for
	   testing from within chroot jails where access to pty devices is
	   locked out.

       -v, --verbose
	   Enable verbose progress reports to stderr. Use multiple times to
	   increase verbosity. It is mainly useful for debugging gpsfake
	   itself.

       -w SEC, --wait SEC
	   Set the timeout on daemon inactivity, in seconds. The default
	   timeout is 60 seconds, and a value of 0 suppresses the timeout
	   altogether.	Note that the actual timeout is longer due to internal
	   delays, typically by about 20 seconds.

       -x, --predump
	   Dump packets as gpsfake gathers them. It is mainly useful for
	   debugging gpsfake itself.

       The last argument(s) must be the name of a file or files containing the
       data to be cycled at the device. gpsfake will print a notification each
       time it cycles.

       Normally, gpsfake creates a pty for each logfile and passes the slave
       side of the device to the daemon. If the header comment in the logfile
       contains the string "UDP", packets are instead shipped via UDP port
       5000 to the address 192.168.0.1.255. You can monitor the packet with
       tcpdump this way:

	   tcpdump -s0 -n -A -i lo udp and port 5000

MAGIC COMMENTS
       Certain magic comments in test load headers can change the conditions
       of the test. These are:

       Serial
	   May contain a serial-port setting such as 4800 7N2 - baud rate
	   followed by 7 or 8 for byte length, N or O or E for parity and 1 or
	   2 for stop bits. The test is run with those settings on the slave
	   port that the daemon sees.

       Transport
	   Values 'TCP' and 'UDP' force the use of TCP and UDP feeds
	   respectively (the default is a pty).

       Delay-Cookie
	   Must be followed by two whitespace-separated fields, a delimiter
	   character and a numeric delay in seconds. Instead of being broken
	   up by packet boundaries, the test load is split on the delimiters.
	   The delay is performed after each feed. Can be useful for imposing
	   write boundaries in the middle of packets.

CUSTOM TESTS
       gpsfake is a trivial wrapper around a Python module, also named
       gpsfake, that can be used to fully script sessions involving a gpsd
       instance, any number of client sessions, and any number of fake GPSes
       feeding the daemon instance with data from specified sentence logs.

       Source and embedded documentation for this module is shipped with the
       gpsd development tools. You can use it to torture test either gpsd
       itself or any gpsd-aware client application.

       Logfiles for the use with gpsfake can be retrieved using gpspipe,
       gpscat, or cgps from the gpsd distribution, or any other application
       which is able to create a compatible output.

ENVIRONMENT
   WRITE_PAD
       For unknown reasons gpsfake may sometimes time out and fail. Set the
       WRITE_PAD environment value to a larger value to avoid this issue. A
       starting point might be "WRITE_PAD = 0.005". Values as large os 0.200
       may be required.

   GPSD_HOME
       If gpsfake exits with "Cannot execute gpsd: executable not found." the
       environment variable GPSD_HOME can be set to the path where gpsd can be
       found. (instead of adding that folder to the PATH environment variable

RETURN VALUES
       0
	   on success.

       1
	   on failure

SEE ALSO
       gpsd(8), gps(1), gpspipe(1), gpscat(1), cgps(1), tcpdump(1), gdb(1),
       lldb(1), valgrind(1)

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

GPSD, Version 3.26.1		  2025-05-15			    GPSFAKE(1)