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How To Configure A Fossil Server
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How To Configure A Fossil Server

Introduction

A server is not necessary to use Fossil, but a server does help in collaborating with peers. A Fossil server also works well as a complete website for a project. For example, the complete https://www.fossil-scm.org/ website, including the page you are now reading, is just a Fossil server displaying the content of the self-hosting repository for Fossil.

This article is a guide for setting up your own Fossil server.

See "How CGI Works In Fossil" for background information on the underlying CGI technology. See "The Fossil Sync Protocol" for information on the wire protocol used for client/server communication.

Overview

There are basically four ways to set up a Fossil server:
  1. A stand-alone server
  2. Using inetd, xinetd, or stunnel
  3. CGI
  4. SCGI (a.k.a. SimpleCGI)

Each of these can serve either a single repository, or a directory hierarchy containing many repositories with names ending in ".fossil".

Standalone server

The easiest way to set up a Fossil server is to use either the server or the ui commands:

The REPOSITORY argument is either the name of the repository file, or a directory containing many repositories named *.fossil. Both of these commands start a Fossil server, usually on TCP port 8080, though a higher numbered port might also be used if 8080 is already occupied. You can access these using URLs of the form http://localhost:8080/, or if REPOSITORY is a directory, URLs of the form http://localhost:8080/repo/ where repo is the base name of the repository file without the ".fossil" suffix.

There are several key differences between "ui" and "server":

You can omit the REPOSITORY argument if you run one of the above commands from within a Fossil checkout directory to serve that repository: 

$ fossil ui          # or...
$ fossil serve

Note that you can abbreviate Fossil sub-commands, as long as they are unambiguous. "server" can currently be as short as "ser".

As a more complicated example, you can serve a directory containing multiple *.fossil files like so: 

$ fossil server --port 9000 --repolist /path/to/repo/dir

There is an example script in the Fossil distribution that wraps fossil server to produce more complicated effects. Feel free to take it, study it, and modify it to suit your local needs.

See the online documentation for more information on the options and arguments you can give to these commands.

Fossil as an inetd/xinetd service

A Fossil server can be launched on-demand by inetd or xinetd using the fossil http command. To launch Fossil from inetd, modify your inetd configuration file (typically "/etc/inetd.conf") to contain a line something like this: 

80 stream tcp nowait.1000 root /usr/bin/fossil /usr/bin/fossil http /home/fossil/repo.fossil

In this example, you are telling "inetd" that when an incoming connection appears on TCP port "80", that it should launch the binary "/usr/bin/fossil" program with the arguments shown. Obviously you will need to modify the pathnames for your particular setup. The final argument is either the name of the fossil repository to be served, or a directory containing multiple repositories.

If you use a non-standard TCP port on systems where the port-specification must be a symbolic name and cannot be numeric, add the desired name and port to /etc/services. For example, if you want your Fossil server running on TCP port 12345 instead of 80, you will need to add: 

fossil          12345/tcp  #fossil server

and use the symbolic name ('fossil' in this example) instead of the numeral ('12345') in inetd.conf. For details, see the relevant section in your system's documentation, e.g. the FreeBSD Handbook in case you use FreeBSD.

If your system is running xinetd, then the configuration is likely to be in the file "/etc/xinetd.conf" or in a subfile of "/etc/xinetd.d". An xinetd configuration file will appear like this: 

service http
{
  port = 80
  socket_type = stream
  wait = no
  user = root
  server = /usr/bin/fossil
  server_args = http /home/fossil/repos/
}

The xinetd example above has Fossil configured to serve multiple repositories, contained under the "/home/fossil/repos/" directory.

In both cases notice that Fossil was launched as root. This is not required, but if it is done, then Fossil will automatically put itself into a chroot jail for the user who owns the fossil repository before reading any information off of the wire.

Inetd or xinetd must be enabled, and must be (re)started whenever their configuration changes - consult your system's documentation for details.

Using inetd or xinetd is a more complex setup than the "standalone" server, but it has the advantage of only using system resources when an actual connection is attempted. If no-one ever connects to that port, a Fossil server will not (automatically) run. It has the disadvantage of requiring "root" access and therefore may not normally be available to lower-priced "shared" servers on the Internet.

The configuration for stunnel is similar, but it is covered in a separate document.

Fossil as CGI

A Fossil server can also be run from an ordinary web server as a CGI program. This feature allows Fossil to be seamlessly integrated into a larger website. CGI is how the self-hosting fossil repositories are implemented.

To run Fossil as CGI, create a CGI script (here called "repo") in the CGI directory of your web server and having content like this: 

#!/usr/bin/fossil
repository: /home/fossil/repo.fossil

As always, adjust your paths appropriately. It may be necessary to set permissions properly, or to modify an ".htaccess" file or make other server-specific changes. Consult the documentation for your particular web server. In particular, the following permissions are normally required (but, again, may be different for a particular configuration):

Once the script is set up correctly, and assuming your server is also set correctly, you should be able to access your repository with a URL like: http://mydomain.org/cgi-bin/repo (assuming the "repo" script is accessible under "cgi-bin", which would be a typical deployment on Apache for instance).

To serve multiple repositories from a directory using CGI, use the "directory:" tag in the CGI script rather than "repository:". You might also want to add a "notfound:" tag to tell where to redirect if the particular repository requested by the URL is not found: 

#!/usr/bin/fossil
directory: /home/fossil/repos
notfound: http://url-to-go-to-if-repo-not-found/

Once deployed, a URL like: http://mydomain.org/cgi-bin/repo/XYZ will serve up the repository "/home/fossil/repos/XYZ.fossil" (if it exists).

Additional options available to the CGI script are documented in the source code. As of 2017-07-02, the available options are described at main.c lines 1777 through 1824.

Fossil as SCGI

The fossil server command, described above as a way of starting a stand-alone web server, can also be used for SCGI. Simply add the --scgi command-line option and the stand-alone server will interpret and respond to the SimpleCGI or SCGI protocol rather than raw HTTP. This can be used in combination with a webserver (such as Nginx) that does not support CGI. A typical Nginx configuration to support SCGI with Fossil would look something like this: 

location /demo_project/ {
    include scgi_params;
    scgi_pass localhost:9000;
    scgi_param SCRIPT_NAME "/demo_project";
    scgi_param HTTPS "on";
}

Note that Fossil requires the SCRIPT_NAME variable in order to function properly, but Nginx does not provide this variable by default, so it is necessary to provide the SCRIPT_NAME parameter in the configuration. Failure to do this will cause Fossil to return an error.

All of the features of the stand-alone server mode described above, 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.

For security, it is probably a good idea to add the --localhost option to the fossil server command to prevent Fossil from accepting off-site connections. One might also want to specify the listening TCP port number, rather than letting Fossil choose one for itself, just to avoid ambiguity. A typical command to start a Fossil SCGI server would be something like this: 

fossil server $REPOSITORY --scgi --localhost --port 9000

Securing a repository with TLS

Fossil's built-in HTTP server (e.g. "fossil server") does not support TLS, but there are multiple ways to protect your Fossil server with TLS. All of this is covered in a separate document, Using TLS-Encrypted Communications with Fossil.

Managing Server Load

A Fossil server is very efficient and normally presents a very light load on the server. The Fossil self-hosting server is a 1/24th slice VM at Linode.com hosting 65 other repositories in addition to Fossil (and including some very high-traffic sites such as http://www.sqlite.org and http://system.data.sqlite.org) and it has a typical load of 0.05 to 0.1. A single HTTP request to Fossil normally takes less than 10 milliseconds of CPU time to complete, so requests can be arriving at a continuous rate of 20 or more per second, and the CPU can still be mostly idle.

However, there are some Fossil web pages that can consume large amounts of CPU time, especially on repositories with a large number of files or with long revision histories. High CPU usage pages include /zip, /tarball, /annotate and others. On very large repositories, these commands can take 15 seconds or more of CPU time. If these kinds of requests arrive too quickly, the load average on the server can grow dramatically, making the server unresponsive.

Fossil provides two capabilities to help avoid server overload problems due to excessive requests to expensive pages:

  1. An optional cache is available that remembers the 10 most recently requested /zip or /tarball pages and returns the precomputed answer if the same page is requested again.

  2. Page requests can be configured to fail with a "503 Server Overload" HTTP error if an expensive request is received while the host load average is too high.

Both of these load-control mechanisms are turned off by default, but they are recommended for high-traffic sites.

The webpage cache is activated using the fossil cache init command-line on the server. Add a -R option to specify the specific repository for which to enable caching. If running this command as root, be sure to "chown" the cache database (which is a separate file in the same directory and with the same name as the repository but with the suffix changed to ".cache") to give it write permission for the userid of the webserver.

To activate the server load control feature visit the Admin → Access setup page in the administrative web interface; in the "Server Load Average Limit" box enter the load average threshold above which "503 Server Overload" replies will be issued for expensive requests. On the self-hosting Fossil server, that value is set to 1.5, but you could easily set it higher on a multi-core server.

The maximum load average can also be set on the command line using commands like this: 

fossil set max-loadavg 1.5
fossil all set max-loadavg 1.5

The second form is especially useful for changing the maximum load average simultaneously on a large number of repositories.

Note that this load-average limiting feature is only available on operating systems that support the "getloadavg()" API. Most modern Unix systems have this interface, but Windows does not, so the feature will not work on Windows. Note also that Linux implements "getloadavg()" by accessing the "/proc/loadavg" file in the "proc" virtual filesystem. If you are running a Fossil instance inside a chroot() jail on Linux, you will need to make the "/proc" file system available inside that jail in order for this feature to work. On the self-hosting Fossil repositories, this was accomplished by adding a line to the "/etc/fstab" file that looks like: 

chroot_jail_proc /home/www/proc proc ro 0 0

The /home/www/proc pathname should be adjusted so that the "/proc" component is in the root of the chroot jail, of course.

To see if the load-average limiter is functional, visit the /test_env page of the server to view the current load average. If the value for the load average is greater than zero, that means that it is possible to activate the load-average limiter on that repository. If the load average shows exactly "0.0", then that means that Fossil is unable to find the load average (either because it is in a chroot() jail without /proc access, or because it is running on a system that does not support "getloadavg()") and so the load-average limiter will not function.