ModernUO Emulator
6b910ff089
Supersedes #2657 (rebased onto #2662, which the original branch conflicted with). Credit to @MithrilHammer for the diagnosis, the fix and the regression tests; their three commits are kept as authored. Fixes #2656. ## Root cause When a guarding pet's combatant hides or becomes invalid, its AI calls `AcquireFocusMob` to find a new target. A controlled creature with no `ControlTarget` (Guard normally has none) fell out of `HandleControlled` and into the wild-creature scan, where `IsEnemy` treats any player as an enemy. With `FightMode.Closest`, the owner won. The fall-through dates to #2232. RunUO never let a controlled creature reach the wild scan. ## Changes - `AcquireFocusMob`: a controlled creature returns whatever `HandleControlled` decides. Guard uses `FindGuardTarget`, Attack uses its `ControlTarget`, and every other order acquires nothing. - `FindGuardTarget` skips guard allies: the master and creatures the master controls, including controlled summons. Uncontrolled summons (energy vortex, blade spirits) attack their caster, so a guard still defends against them, as in RunUO. - Friendly fire: `BaseAI.OnAggressiveAction` stands a guard down when an ally is the aggressor. `BaseCreature.Combatant` refuses an ally while guarding, because `Mobile.AggressiveAction` assigns the first aggressor as `Combatant` before any retaliation policy runs. The veto sits on `Combatant` rather than `CanBeHarmful`, so what a pet can harm doesn't depend on its current order. An explicit Attack order and bard provocation can still target an ally. ## Tests 16 regression cases in `GuardFriendlyFireTests` (skipped without client map data), including a real `WhiteWyrm` reproduction. `UOContent.Tests`: 1142 passed, 2 skipped, 0 failed on Windows. |
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| tools | ||
| .cursorrules | ||
| .editorconfig | ||
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| AGENTS.md | ||
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| CLAUDE.md | ||
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| CONTRIBUTING.md | ||
| Directory.Build.props | ||
| FAQ.md | ||
| GEMINI.md | ||
| global.json | ||
| LICENSE | ||
| ModernUO.slnx | ||
| publish.cmd | ||
| publish.ps1 | ||
| publish.sh | ||
| README.md | ||
| rider-settings.zip | ||
| Rules.ruleset | ||
| SPONSORS.md | ||
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ModernUO 
Ultima Online Server Emulator for the modern era!
Requirements
Supported Operating Systems
Required Frameworks
All Operating Systems
Windows
Hardware
| Use | vCPU | RAM | Storage |
|---|---|---|---|
| Development / test | 2 dedicated | 2 GB | SSD |
| Small live shard (< 50 concurrent) | 4 dedicated | 4 GB | NVMe |
| Medium (50–200) | 4–8 | 8 GB | NVMe |
| Large (200+) | 8+, high clock | 16 GB+ | NVMe |
See dev-docs/server-requirements.md for more information.
Development
Supported IDEs
Getting Started
- Install prerequisite requirements
- Clone this repository (or download the latest):
git clone https://github.com/modernuo/ModernUO.git
- Open
ModernUO.slnto start developing
Building/Publishing
Interactive Mode (Recommended for new users)
Run ./publish.cmd (Windows) or ./publish.sh (Linux/macOS) with no arguments to launch the guided build tool. It will:
- Check prerequisites (.NET SDK, native libraries)
- Walk you through configuration and platform selection
- Build and publish the server to the
Distributiondirectory - Show deployment instructions for cross-compiled builds
Command Line
./publish.cmd [release|debug] [os] [arch]
os- Supported operating systemsarchx64- Intel/AMD 64-bitarm64- ARM 64-bit
Linux Prerequisites
Fedora, CentOS, RHEL, AlmaLinux, Rocky, etc
dnf upgrade --refresh -y
# RHEL-family distributions (CentOS Stream, AlmaLinux, Rocky, RHEL) need CRB and EPEL enabled.
# Fedora skips this block.
dnf install -y dnf-plugins-core
dnf config-manager --set-enabled crb
dnf install -y epel-release
# Prerequisites
dnf install -y findutils libicu libdeflate libargon2 tzdata
Ubuntu, Debian, etc
apt-get update -y
# The ICU runtime package carries the ABI version in its name (libicu74, libicu76, …) and has no
# stable alias, so match it by pattern rather than pinning a release-specific name.
apt-get install -y '^libicu[0-9]+$' libdeflate0 libargon2-1 tzdata
Only the runtime libraries are needed — the -dev/-devel packages are not. Run
./build-tool --check-prereqs to check the current machine and print the exact packages your
release needs.
zstd is not listed because ZstdNet bundles libzstd for every platform, and liburing is not
listed because IORingGroup issues io_uring syscalls directly.
If the shard's configured time zone is a legacy alias such as US/Eastern, Debian 12 and Ubuntu
24.04 also need tzdata-legacy. See Platform Prerequisites
for what each dependency is for and what breaks without it.
OSX Requirements
brew install icu4c libdeflate argon2
Running the Server
- Follow the publish instructions
- The
Distributiondirectory is portable — copy it to your production server for deployment - Run
ModernUO.exeordotnet ModernUO.dllfrom theDistributiondirectory - On first run, the server will prompt you to configure game data file locations
Troubleshooting / FAQ
- See FAQ
Want to sponsor?
Thank you for supporting us! You can find out how by visiting the sponsors page.
Collaborators
Thanks
- RunUO Team & Community
- Voxpire, the ServUO Team & Community
- Karasho, Jaedan and the ClassicUO Community
Development Tools & Plugins provided with ♥ by
Code Signing Policy
Free code signing provided by SignPath.io, certificate by SignPath Foundation.
This program will not transfer any information to other networked systems unless specifically requested by the user or the person installing or operating it
Teams & Roles
Approvers & Committers: Development Team