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[FATAL ERROR: Could not find system resources]

This message is associated with two situations

  • Broken installations
  • Prolog is embedded in a C/C++/Java/... application

On calling PL_initialise(), SWI-Prolog searches for a saved-state holding the Prolog predicates that make up the system (or your application). If it fails, it will print the message above and exit.

First, it checks the command line argument --home=Dir. If this option is lacking it will try to identify the running executable. If successful (which requires passing argv[0] from main() on Unix and nothing special on Windows) and the executable contains a state at the end, it is loaded.

Second, it tries to locate the SWI-Prolog home directory. For this, it first checks the environment variable SWI_HOME_DIR. If it exists and points to something that looks like the home-directory it uses this directory. If not, it assumes this executable is installed in the bin directory of the installation (Unix: bin/_architecture_). On Windows, it also looks for the folder from which libswipl.dll was loaded, again expecting this to be the bin directory of the Prolog home. Finally, it will use the compiled-in installation directory. It expects the system state in the file boot.prc in the home directory.

This poses problems for embedded applications that do not have a saved-state associated (see the swipl-ld program), are not installed in the same directory as the SWI-Prolog executable and SWI-Prolog is installed as binary package (the compiled-in default is wrong).


On Windows, it suffices to leave libswipl.dll in the installation tree (i.e., do not copy it elsewhere) and add the bin directory of the installation tree to %PATH%.

A cross-platform and robust solution is to use putenv() to put an appropriate path into the environment before calling PL_initialise().

        putenv("SWI_HOME_DIR=C:\\Program Files\\swipl");
        if ( PL_initialise(argc, argv) )

In the final version of your application you link the saved-state to the executable (using swipl-ld or cat (Unix)) and comment the putenv() call.

Finding the home directory

You can find SWI-Prolog's notion of home from within Prolog using

?- current_prolog_flag(home, Home).
Home = '...'

Or from the shell (for scripting/configuration) using one of the the commands below. The first just prints the home directory, the second dumps a shell script that sets variables that describe the Prolog configuration.

swipl --home

swipl --dump-runtime-variables