Advanced configuration topics

Adding graphics, custom styling and custom JavaScript

DOMjudge can optionally present country flags, affiliation logos, team pictures and a page-wide banner on the public interface.

You can place the images under the path public/images/ (see the Config checker in the admin interface for the full filesystem path of your installation) as follows:

  • Country flags are shown when the show_flags configuration option is enabled. The flag-icon-css is used for the flag images.

  • Affiliation logos: these will be shown with the teams that are part of the affiliation, if the show_affiliation_logos configuration option is enabled. They can be placed in public/images/affiliations/1234.png where 1234 is the external ID of the affiliation as shown in the DOMjudge interface. There is a separate option show_affiliations that independently controls where the affiliation names are shown on the scoreboard. These logos should be square and be at least 64x64 pixels, but not much bigger.

  • Team pictures: a photo of the team will be shown in the team details page if public/images/teams/456.jpg exists, where 456 is the team’s external ID as shown in the DOMjudge interface. DOMjudge will not modify the photos in any way or form, so make sure you don’t upload photos that are too big, since that will incur a lot of network traffic.

  • Contest Banners: a page-wide banner can be shown on the public scoreboard if that image is placed in public/images/banners/1.png where 1 is the contest’s external ID as shown in the DOMjudge interface. Alternatively, you can place a file at public/images/banner.png which will be used as a banner for all contests. Contest-specific banners always have priority. Contest banners usually are rectangular, having a width of around 1920 pixels and a height of around 300 pixels. Other ratio’s and sizes are supported, but check the public scoreboard to see how it looks.

It is also possible to load custom CSS and/or JavaScript files. To do so, place files ending in .css under public/css/custom/ and/or files ending in .js under public/js/custom/. See the Config checker in the admin interface for the full filesystem path of your installation. Note that there is no guaranteed order in which the files will be loaded, but they will all be loaded after the main DOMjudge CSS and JavaScript files. If you have a lot of custom CSS/JavaScript files in these directories, the response time of DOMjudge might decrease, so it is recommended to only place a few files there.


If you add or remove any of the above files, you need to clear the cache for changes to be detected.

Authentication and registration

Out of the box users are able to authenticate using username and password.

Two other native authentication methods are available:

  • IP Address - authenticates users based on the IP address they are accessing the system from;

  • X-Headers - authenticates users based on some HTTP header values.

Besides this, DOMjudge can be configured with any provider that can set the environment variable REMOTE_USER to an existing username, for example LDAP, SAML, CAS or OpenID connect modules for Apache.

There’s an option to let teams register themselves in the system.

IP Address

To enable the IP Address authentication method, you will need to edit the configuration option auth_methods to include ipaddress.

Once this is done, when a user first logs in their IP address will be associated with their account, and subsequent logins will allow them to log in without authenticating.

If desired, you can edit or pre-fill the IP address associated with an account from the Users page. When using IPv6, ensure that you enter the address in the exact representation as the webserver reports it (e.g. as visible in the webserver logs) - no canonicalization is performed.


To enable the X-Headers authentication method, you will need to edit the configuration option auth_methods to include xheaders.

To use this method, the following HTTP headers need to be sent to the /login URL. This can be done using the squid proxy for example, to prevent teams from needing to know their own log in information but in an environment where IP address based auth is not feasible (multi site over the internet contest).

  • X-DOMjudge-Login - Contains the username

  • X-DOMjudge-Pass - Contains the user’s password, base64 encoded

Squid configuration for this might look like:

acl autologin url_regex ^http://localhost/domjudge/login
request_header_add X-DOMjudge-Login "$USERNAME" autologin
request_header_add X-DOMjudge-Pass "$BASE64_PASSWORD" autologin


DOMjudge supports generic authentication by various existing providers that can authenticate a user and set the REMOTE_USER environment variable to the authenticated username.

Examples of this are several Apache modules: mod LDAP, Shibboleth or Mod Mellon for SAML 2.0, mod Auth CAS, mod OpenID Connect, or mod Kerb for Kerberos.

This does not currently allow for auto-provisioning or self-registration, the users must already exist in DOMjudge and their DOMjudge username must match what is in the REMOTE_USER variable.

Set up the respective module to authenticate incoming users for the URL path of your installation. Then, in webapp/config/packages/security.yaml change the main section of your source tree to add a remote_user key after form_login that looks like this:

    pattern: ^/
        login_path: login
        check_path: login
        csrf_token_generator: security.csrf.token_manager
        use_referer: true
        provider: domjudge_db_provider

And re-run the “make install” command to deploy this change. Or alternatively remove the entire var/cache/prod/ directory when editing security.yaml on an already deployed location.

If the thus authenticated user is not found in DOMjudge, the application will present the standard username/password login screen as a fallback.

Changing the User password hashing cost

The hashing cost can be changed in webapp/config/packages/security.yaml, change the encoder section:


algorithm: ‘bcrypt’ cost: 7

For bcrypt (current encoder) each increase in cost will double the time per password.

See the Symfony docs for more info on this subject.


Teams can be allowed to self-register with the system. To enable it, go to the team category you want the self-registered teams to become part of and enable self-registration for that category. The option will be shown on the login screen if it has been enabled for at least one category. When multiple categories are set to allow, teams can choose one of them during registration. You can assign the respective categories to the contest(s) these teams may participarte in.

During registration, teams can also specify their affiliation, if the global configuration option ‘show affiliations’ is enabled.


DOMjudge supports executable archives (uploaded and stored in ZIP format) for configuration of languages, special run and compare programs. The archive must contain an executable file named build or run. When deploying a new (or changed) executable to a judgehost build is executed once if present (inside the chroot environment that is also used for compiling and running submissions). Afterwards an executable file run must exist (it may have existed before), that is called to execute the compile, compare, or run script. The specific formats are detailed below.

Executables may be changed via the web interface in an online editor or by uploading a replacement zip file. Changes apply immediately to all further uses of that executable.

Programming languages

Compilers can be configured by creating or selecting/editing an executable in the web interface. When compiling a set of source files, the run executable is invoked with the following arguments: destination file name, memory limit (in kB), main (first) source file, other source files. For more information, see for example the executables c or java_javac_detect in the web interface. For many common languages compile scripts are already included.

Interpreted languages and non-statically linked binaries (for example, Python or Java) can in also be used, but require that all runtime dependencies are added to the chroot environment. For details, see the section Creating a chroot environment.

Interpreted languages do not generate an executable and in principle do not need a compilation step. However, to be able to use interpreted languages (also Python and Java), during the compilation step a script must be generated that will function as the executable: the script must run the interpreter on the source. See for example pl and java_javac_detect in the list of executables.

Special run and compare programs

To allow for problems that do not fit within the standard scheme of fixed input and/or output, DOMjudge has the possibility to change the way submissions are run and checked for correctness.

The back end script that handles the running and checking of submissions, calls separate programs for running submissions and comparison of the results. These can be specialised and adapted to the requirements per problem. For this, one has to create executable archives as described above. Then the executable must be selected in the special_run and/or special_compare fields of the problem (an empty value means that the default run and compare scripts should be used; the defaults can be set in the global configuration settings). When creating custom run and compare programs, we recommend re-using wrapper scripts that handle the tedious, standard part. See the boolfind example for details.

Compare programs

Compare scripts/programs should follow the Output Validators format DOMjudge uses the default output validator from the problem package format as its default.

Note that DOMjudge only supports a subset of the functionality described there. In particular, the calling syntax is:

/path/to/compare_script/run <> <testdata.ans> <feedbackdir> <compare_args> < <program.out>;

where testdata.ans are the jury reference input and output files, feedbackdir the directory containing the judging response files judgemessage.txt and judgeerror.txt, compare_args a list of arguments that can set when configuring a contest problem, and program.out the team’s output. The validator program should not make any assumptions on its working directory.

For more details on writing and modifying a compare (or validator) script, see the boolfind_cmp example and the comments at the top of the file

Run programs

Special run programs can be used, for example, to create an interactive problem, where the contestants’ program exchanges information with a jury program and receives data depending on its own output. The problem boolfind is included as an example interactive problem, see doc/examples/boolfind.pdf for the description.

The calling syntax is:

/path/to/run_script/run <> <testdata.ans> <feedbackdir> <run args> < <program.out>;

Usage is similar to compare programs. DOMjudge wraps the run program to handle bi-directional communication between the run program and the contestants’ program. Anything you write to stdout is forwarded to the contestants’ program, anything the contestants’ program writes is forwarded to your stdin.

See the validate.h file in the boolfind_run executable for some convenience functions you might want to use when implementing your own run program.


It is recommended to configure the local desktop printing of team workstations where ever possible: this has the most simple interface and allows teams to print from within their editor.

If this is not feasible, DOMjudge includes support for printing via the DOMjudge web interface: the DOMjudge server then needs to be able to deliver the uploaded files to the printer. It can be enabled via the print_command configuration option in the administrator interface. Here you can enter a command that will be run to print the files. The command you enter can have the following placeholders:

  • [file]: the location on disk of the file to print.

  • [original]: the original name of the file.

  • [language]: the ID of the language of the file. Useful for syntax highlighting.

  • [username]: the username of the user who is printing.

  • [teamname]: the teamname of the user who is printing.

  • [teamid]: the team ID of the user who is printing.

  • [location]: the location of the user’s team.

[language], [teamname], [teamid] and [location] can be empty. Placeholders will be shell-escaped before passing them to the command. The standard output of the command will be shown in the web interface. If you also want to show standard error, add 2>&1 to the command.

For example, to send the first 10 pages of the file to the default printer using enscript and add the username in the page header, you can use this command:

enscript -b [username] -a 0-10 -f Courier9 [file] 2>&1

Multiple judgedaemons per machine

You can run multiple judgedaemons on one multi-CPU or multi-core machine, dedicating one CPU core to each judgedaemon using Linux cgroups.

To that end, add extra unprivileged users to the system, i.e. add users domjudge-run-X (where X runs through 1,2,3,...) with useradd as described in the section Building and installing.

You can then start each of the judgedaemons with:

judgedaemon -n X

to bind it to core X and user domjudge-run-X. If you use systemd, then edit the unit file and add more judgedaemons there.

Although each judgedaemon process will be bound to one single CPU core, shared use of other resources such as disk I/O might still have effect on run times.

Multi-site contests

This manual assumed you are running a singe-site contest; that is, the teams are located closely together, probably in a single physical location. In a multi-site or distributed contest, teams from several remote locations use the same DOMjudge installation. An example is a national contest where teams can participate at their local institution.

One option is to run a central installation of DOMjudge to which the teams connect over the internet. It is here where all submission processing and judging takes place. Because DOMjudge uses a web interface for all interactions, teams and judges will interface with the system just as if it were local. Still, there are some specific considerations for a multi-site contest.

Network: there must be a relatively reliable network connection between the locations and the central DOMjudge installation, because teams cannot submit or query the scoreboard if the network is down. Because of traversing an unsecured network, you should consider HTTPS for encrypting the traffic. If you want to limit teams’ internet access, it must be done in such a way that the remote DOMjudge installation can still be reached.

Team authentication: the IP-based authentication will still work as long as each team workstation has a different public IP address. If some teams are behind a NAT-router and thus all present themselves to DOMjudge with the same IP-address, another authentication scheme must be used (e.g. PHP sessions).

Judges: if the people reviewing the submissions will be located remotely as well, it’s important to agree beforehand on who-does-what, using the submissions claim feature and how responding to incoming clarification requests is handled. Having a shared chat/IM channel may help when unexpected issues arise.

Scoreboard: by default DOMjudge presents all teams in the same scoreboard. Per-site scoreboards can be implemented either by using team categories or team affiliations in combination with the scoreboard filtering option.

As an alternative, each site can run their own DOMjudge installation, and each site will have a local scoreboard with their own teams. It is possible to create a merged scoreboard out of these individual installations with the console command scoreboard:merge. You need to know for each site which contest ID to use, and the IDs of the team categories you want to include (comma separated). You can then run it like this:

webapp/bin/console scoreboard:merge 'Combined Scoreboard Example' \ 3 \ 2,3  \ 3

Clearing the PHP/Symfony cache

Some operations require you to clear the PHP/Symfony cache. To do this, execute the webapp/bin/console (see the Config checker in the admin interface for the full filesystem path of your installation) binary with the cache:clear subcommand:

webapp/bin/console cache:clear

Note that this is different than clearing the scoreboard cache.

Sending errors to Sentry

DOMjudge has the possibility to send any errors to Sentry. First, create an organization and project in Sentry and copy the Sentry DSN. Then create the file webapp/.env.local and add to it the setting SENTRY_DSN=<dsn> where <dsn> is the Sentry DSN you copied. Then clear the cache for this change to take effect. Now all errors should appear in Sentry automatically.