Fossil: Serving via SCGI

Fossil SCM

There is an alternative to running Fossil as a standalone HTTP server, which is to run it in SimpleCGI (a.k.a. SCGI) mode, which uses the same fossil server command as for HTTP service. Simply add the --scgi command-line option and the stand-alone server will speak the SCGI protocol rather than raw HTTP.

This can be used with a web server such as nginx which does not support Fossil’s CGI mode.

A basic nginx configuration to support SCGI with Fossil looks like this:

    location /code/ {
        include scgi_params;
        scgi_param SCRIPT_NAME "/code";
        scgi_pass localhost:9000;
    }

The scgi_params file comes with nginx, and it simply translates nginx internal variables to scgi_param directives to create SCGI environment variables for the proxied program; in this case, Fossil. Our explicit scgi_param call to define SCRIPT_NAME adds one more variable to this set, which is necessary for this configuration to work properly, because our repo isn’t at the root of the URL hierarchy. Without it, when Fossil generates absolute URLs, they’ll be missing the /code part at the start, which will typically cause 404 errors.

The final directive simply tells nginx to proxy all calls to URLs under /code down to an SCGI program on TCP port 9000. We can temporarily set Fossil up as a server on that port like so:

    $ fossil server /path/to/repo.fossil --scgi --localhost --port 9000 &

The --scgi option switches Fossil into SCGI mode from its default, which is stand-alone HTTP server mode. All of the other options discussed in that linked document — such as the ability to serve a directory full of Fossil repositories rather than just a single repository — work the same way in SCGI mode.

The --localhost option is simply good security: we’re using nginx to expose Fossil service to the outside world, so there is no good reason to allow outsiders to contact this Fossil SCGI server directly.

Giving an explicit non-default TCP port number via --port is a good idea to avoid conflicts with use of Fossil’s default TCP service port, 8080, which may conflict with local uses of fossil ui and such.

We characterized the SCGI service start command above as “temporary” because running Fossil in the background like that means it won’t start back up on a reboot of the server. A simple solution to that is to add that command to /etc/rc.local on systems that have it. However, you might want to consider setting Fossil up as an OS service instead, so that you get the benefits of the platform’s service management framework:

We go into more detail on nginx service setup with Fossil in our Debian/Ubuntu specific guide. Then in a later article that builds upon that, we show how to add TLS encryption to this basic SCGI + nginx setup on Debian type OSes.

Return to the top-level Fossil server article.