Highly Performant & Scalable Ultima Online Server Emulator
https://www.modernuo.com
c-sharpcsharpcsharp-coredotnetdotnet-coreemulatorgplgplv3mmommo-enginemmorpgmmorpg-serveronlinerpgrunuoserverservuoultimaultima-onlineuo
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## Why `PlayerConstructed` is per-instance provenance, and #2574 put it on every crafted item — including potions, arrows and other stackables. Stack operations were written when no item carried provenance of any kind, so they treated two piles of the same graphic as interchangeable. **Merging** keeps the receiving stack's value. Dropping bought potions onto a crafted stack made the whole pile count as crafted; the reverse order erased it. Which one happened was decided by drag direction alone. **Splitting** rebuilds one half in `Mobile.LiftItemDupe`, which copies a fixed list of fields rather than going through `Dupe`/`CopyProperties`. `PlayerConstructed` was not on that list, so dragging part of a pile off stripped the new half. Worth calling out: `[IgnoreDupe]` does **not** govern this path — it only applies to `Dupe()`. Reasoning "the field isn't `[IgnoreDupe]`, so it copies" is wrong here. ## Changes - `Item.CanStackWith` compares `PlayerConstructed`, so crafted and non-crafted never merge into one indistinguishable pile. - `Mobile.LiftItemDupe` copies `PlayerConstructed` onto the remainder, so a split cannot produce halves that disagree about what they are. Refusing to merge is the whole fix. A stack has nowhere to record provenance, so the only coherent behaviour is to keep the two piles apart rather than pick a winner. ## What this deliberately does not do Paths that genuinely **virtualize** an item — pouring from a `PotionKeg`, for one — rebuild it without the flag, and the result is simply treated as not crafted. That is accepted rather than worked around; the alternative is threading provenance through every count-based container, which buys little. The keg stores a `Held` int rather than a stack, so nothing there depends on merging and nothing breaks. `CommodityDeed` is unaffected — it holds the real `Commodity` item rather than a count, so the flag rides along. ## Player-visible effect Crafted potions and arrows will no longer stack with bought or looted ones. That is the intended invariant, and it is the reason the flag can be trusted at all. ## Tests 7 new tests in `Server.Tests`: both merge directions, the matching-provenance case, split copying, and the split/re-merge round trip. `Server.Tests` **822 passing**, `UOContent.Tests` **701 passing**, build clean with 0 warnings. |
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| branding | ||
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| Distribution/Data | ||
| Projects | ||
| tools | ||
| .cursorrules | ||
| .editorconfig | ||
| .gitattributes | ||
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| AGENTS.md | ||
| azure-pipelines.yml | ||
| CLAUDE.md | ||
| CODE_OF_CONDUCT.md | ||
| 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 | ||
| stylecop.json | ||
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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 |
Game logic is single-threaded, so single-core clock speed matters more than core count, and dedicated vCPU matters more than either — burstable or shared plans throttle once credits run out, which is the most common cause of unexplained lag spikes. Save size drives RAM more than player count does.
See dev-docs/server-requirements.md for the reasoning and tuning options.
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