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The judge component of the DMOJ: Modern Online Judge platform

Project description

DMOJ Judge amd64 Build Status arm64 Build Status FreeBSD Build Status Coverage Slack

Python AGPLv3 contest judge backend for the DMOJ site interface. See it in action at!

A modern online judge and contest platform system, supporting IO-based, interactive, and signature-graded tasks, with runtime data generators and custom output validators.

Supported Platforms and Runtimes

The judge implements secure grading on Linux and FreeBSD machines.

Linux FreeBSD
x86 ¯\_(ツ)_/¯

Versions up to and including v1.4.0 also supported grading on Windows machines.

The DMOJ judge does not need a root user to run on Linux machines: it will run just fine under a normal user.

Supported languages include:

  • C++ 11/14/17/20 (GCC and Clang)
  • C 99/11
  • Java 8/9/10/11/15
  • Python 2/3
  • PyPy 2/3
  • Pascal
  • Perl
  • Mono C#/F#/VB

The judge can also grade in the languages listed below. These languages are less tested and more likely to be buggy.

  • Ada
  • AWK
  • D
  • Dart
  • Fortran
  • Forth
  • Go
  • Groovy
  • Haskell
  • Kotlin
  • Lua
  • NASM
  • Objective-C
  • OCaml
  • PHP
  • Pike
  • Prolog
  • Racket
  • Ruby
  • Rust
  • Scala
  • Chicken Scheme
  • sed
  • Steel Bank Common Lisp
  • Swift
  • Tcl
  • Turing
  • V8 JavaScript
  • Brain****
  • Zig


Installing the DMOJ judge creates two executables in your Python's script directory: dmoj and dmoj-cli. dmoj is used to connect a judge to a DMOJ site instance, while dmoj-cli provides a command-line interface to a local judge, useful for testing problems.

For more detailed steps, read the installation instructions.

Note that the only officially-supported Linux distribution is the latest Debian, with the default apt versions of all runtimes. This is what we run on, and it should "just work". While the judge will likely still work with other distributions and runtime versions, some runtimes might fail to initialize. In these cases, please file an issue.

Stable Build

PyPI version PyPI

We periodically publish builds on PyPI. This is the easiest way to get started, but may not contain all the latest features and improvements.

$ pip install dmoj

Bleeding-Edge Build

This is the version of the codebase we run live on

$ git clone --recursive
$ cd judge-server
$ pip install -e .

Several environment variables can be specified to control the compilation of the sandbox:

  • DMOJ_USE_SECCOMP; set it to no if you're building on a pre-Linux 3.5 kernel to disable seccomp filtering in favour of pure ptrace (slower). This flag has no effect when building outside of Linux.
  • DMOJ_TARGET_ARCH; use it to override the default architecture specified for compiling the sandbox (via -march). Usually this is native, but will not be specified on ARM unless DMOJ_TARGET_ARCH is set (a generic, slow build will be compiled instead).

With Docker

We maintain Docker images with all runtimes we support in the runtimes-docker project.

Runtimes are split into three tiers of decreasing support. Tier 1 includes Python 2/3, C/C++ (GCC only), Java 8, and Pascal. Tier 3 contains all the runtimes we run on Tier 2 contains some in-between mix; read the Dockerfile for each tier for details. These images are rebuilt and tested every week to contain the latest runtime versions.

The script below spawns a tier 1 judge image. It expects the relevant environment variables to be set, the network device to be enp1s0, problems to be placed under /mnt/problems, and judge-specific configuration to be in /mnt/problems/judge.yml. Note that runtime configuration is already done for you, and will be merged automatically into the judge.yml provided.

$ git clone --recursive
$ cd judge-server/.docker
$ make judge-tier1
$ exec docker run \
    --name judge \
    -p "$(ip addr show dev enp1s0 | perl -ne 'm@inet (.*)/.*@ and print$1 and exit')":9998:9998 \
    -v /mnt/problems:/problems \
    --cap-add=SYS_PTRACE \
    -d \
    --restart=always \
    dmoj/judge-tier1:latest \
    run -p15001 -s -c /problems/judge.yml \


Running a Judge Server

$ dmoj --help
usage: dmoj [-h] [-p SERVER_PORT] -c CONFIG [-l LOG_FILE] [--no-watchdog]
            [-a API_PORT] [-A API_HOST] [-s] [-k] [-T TRUSTED_CERTIFICATES]
            [-e ONLY_EXECUTORS | -x EXCLUDE_EXECUTORS] [--no-ansi]
            server_host [judge_name] [judge_key]

Spawns a judge for a submission server.

positional arguments:
  server_host           host to connect for the server
  judge_name            judge name (overrides configuration)
  judge_key             judge key (overrides configuration)

optional arguments:
  -h, --help            show this help message and exit
  -p SERVER_PORT, --server-port SERVER_PORT
                        port to connect for the server
  -c CONFIG, --config CONFIG
                        file to load judge configurations from
  -l LOG_FILE, --log-file LOG_FILE
                        log file to use
  --no-watchdog         disable use of watchdog on problem directories
  -a API_PORT, --api-port API_PORT
                        port to listen for the judge API (do not expose to
                        public, security is left as an exercise for the
                        reverse proxy)
  -A API_HOST, --api-host API_HOST
                        IPv4 address to listen for judge API
  -s, --secure          connect to server via TLS
  -k, --no-certificate-check
                        do not check TLS certificate
                        use trusted certificate file instead of system
  -e ONLY_EXECUTORS, --only-executors ONLY_EXECUTORS
                        only listed executors will be loaded (comma-separated)
                        prevent listed executors from loading (comma-
  --no-ansi             disable ANSI output
  --skip-self-test      skip executor self-tests

Running a CLI Judge

$ dmoj-cli --help
usage: dmoj-cli [-h] -c CONFIG
                [-e ONLY_EXECUTORS | -x EXCLUDE_EXECUTORS]

Spawns a judge for a submission server.

optional arguments:
  -h, --help            show this help message and exit
  -c CONFIG, --config CONFIG
                        file to load judge configurations from
  -e ONLY_EXECUTORS, --only-executors ONLY_EXECUTORS
                        only listed executors will be loaded (comma-separated)
                        prevent listed executors from loading (comma-
  --no-ansi             disable ANSI output
  --skip-self-test      skip executor self-tests


For info on the problem file format and more, read the documentation.

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