DMOJ Judge

Contest judge backend for the DMOJ site interface, supporting IO-based, interactive, and signature-graded tasks, with runtime data generators and custom output validators.

See it in action at dmoj.ca!

Supported platforms and runtimes

The judge implements secure grading on Linux and FreeBSD machines.

| | Linux | FreeBSD | | --: | :---: | :-----: | | x64 | ✔ | ✔ | | x86 | ✔ | ¯\\\(ツ)\/¯ | | x32 | ✔ | — | | ARM | ✔ | ❌ |

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

Versions up to and including v3.0.2 also supported grading with pure ptrace without seccomp, which is useful on Linux kernel versions before 4.8.

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++ 11/14/17/20/23 (GCC and Clang)
• C 99/11
• Java 8/25
• Python 2/3
• PyPy 2/3
• Pascal
• Mono C#/F#/VB

The judge can also grade in the languages listed below:

• Ada
• Algol 68
• AWK

Brain\\\\*

• COBOL
• D
• Dart
• Forth
• Fortran
• Go
• Groovy
• Haskell
• INTERCAL
• JavaScript (Node.js and V8)
• Kotlin
• Lean 4
• LLVM IR
• Lua
• NASM
• Objective-C
• OCaml
• Perl
• PHP
• Pike
• Prolog
• Racket
• Ruby
• Rust
• Scala 3
• Chicken Scheme
• sed
• Steel Bank Common Lisp
• Swift
• Tcl
• Turing
• V8 JavaScript
• Zig

Installation

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 Linux distribution with first-class support is the latest Debian, with the default apt versions of all runtimes. This is what we run on dmoj.ca, 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

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 dmoj.ca.

$ git clone --recursive https://github.com/DMOJ/judge-server.git
$ cd judge-server
$ pip install -e .

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

• DMOJTARGETARCH; 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 DMOJTARGETARCH 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 dmoj.ca. 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 https://github.com/DMOJ/judge-server.git
$ cd judge-server/.docker
$ make judge-tier1
$ exec docker run \
    --name judge \
    -p "$(ip addr show dev enp1s0 | perl -ne 'm@inet (.)/.@ and print$1 and exit')":9998:9998 \
    -v /mnt/problems:/problems \
    --cap-add=SYS_PTRACE \
    -d \
    --restart=always \
    dmoj/judge-tier1:latest \
    run -p15001 -s -c /problems/judge.yml \
    "$BRIDGEADDRESS" "$JUDGENAME" "$JUDGE_KEY"

Usage

Running a judge server

$ dmoj --help
usage: dmoj [-h] [-p SERVERPORT] -c CONFIG [-l LOGFILE] [--no-watchdog]
            [-a APIPORT] [-A APIHOST] [-s] [-k] [-T TRUSTED_CERTIFICATES]
            [-e ONLYEXECUTORS | -x EXCLUDEEXECUTORS] [--no-ansi]
            serverhost [judgename] [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 SERVERPORT, --server-port SERVERPORT                         port to connect for the server   -c CONFIG, --config CONFIG                         file to load judge configurations from   -l LOGFILE, --log-file LOGFILE                         log file to use   --no-watchdog         disable use of watchdog on problem directories   -a APIPORT, --api-port APIPORT                         port to listen for the judge API (do not expose to                         public, security is left as an exercise for the                         reverse proxy)   -A APIHOST, --api-host APIHOST                         IPv4 address to listen for judge API   -s, --secure          connect to server via TLS   -k, --no-certificate-check                         do not check TLS certificate   -T TRUSTEDCERTIFICATES, --trusted-certificates TRUSTEDCERTIFICATES                         use trusted certificate file instead of system   -e ONLYEXECUTORS, --only-executors ONLYEXECUTORS                         only listed executors will be loaded (comma-separated)   -x EXCLUDEEXECUTORS, --exclude-executors EXCLUDEEXECUTORS                         prevent listed executors from loading (comma-                         separated)   --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 ONLYEXECUTORS | -x EXCLUDEEXECUTORS]
                [--no-ansi]
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 ONLYEXECUTORS, --only-executors ONLYEXECUTORS                         only listed executors will be loaded (comma-separated)   -x EXCLUDEEXECUTORS, --exclude-executors EXCLUDEEXECUTORS                         prevent listed executors from loading (comma-                         separated)   --no-ansi             disable ANSI output   --skip-self-test      skip executor self-tests

Documentation

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