diff --git a/CLAUDE.md b/CLAUDE.md
index 7f24661a4..924255249 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -46,6 +46,7 @@ Apply these when writing or reviewing `.cs` files under `Projects/`.
| Event system | `dev-docs/events.md` |
| Threading model | `dev-docs/threading-model.md` |
| Server lifecycle & bootstrap phases (Configure/ConfigurePrompts/Initialize) | `dev-docs/server-lifecycle.md` |
+| Platform prerequisites (ICU, tzdata, native libs per distro) | `dev-docs/platform-prerequisites.md` |
| Configuration system | `dev-docs/configuration.md` |
| Networking & packets | `dev-docs/networking-packets.md` |
| IP bans, blocklists & allowlists (incl. unblocking a player) | `dev-docs/ip-bans-and-allowlists.md` |
diff --git a/Projects/BuildTool/Prerequisites/NativeLibraryChecker.cs b/Projects/BuildTool/Prerequisites/NativeLibraryChecker.cs
index 8050f6533..95c521c24 100644
--- a/Projects/BuildTool/Prerequisites/NativeLibraryChecker.cs
+++ b/Projects/BuildTool/Prerequisites/NativeLibraryChecker.cs
@@ -32,9 +32,10 @@ public static class NativeLibraryChecker
"Linux",
[
".NET 10 Runtime — https://dotnet.microsoft.com/download/dotnet/10.0",
- "Debian/Ubuntu: sudo apt-get install -y libdeflate0 libargon2-1 libicuNN",
+ "Debian/Ubuntu: sudo apt-get install -y libdeflate0 libargon2-1 libicuNN tzdata",
" (libicuNN varies by release, e.g. libicu76 — run build-tool --check-prereqs there for the exact name)",
- "Fedora/RHEL: sudo dnf install -y libdeflate libargon2 libicu",
+ " (add tzdata-legacy if the shard is configured with an alias such as US/Eastern)",
+ "Fedora/RHEL: sudo dnf install -y libdeflate libargon2 libicu tzdata",
"CentOS: Also requires epel-release and CRB enabled"
]
),
@@ -179,49 +180,25 @@ public static class NativeLibraryChecker
}
///
- /// Libraries the server needs from the system on Linux.
- ///
- /// zstd is absent because ZstdNet bundles libzstd for every RID. liburing is absent because
- /// IORingGroup issues io_uring syscalls directly and imports only libc, libSystem.dylib,
- /// kernel32.dll, kernelbase.dll and ws2_32.dll.
- ///
- /// ICU is here because the server does not set InvariantGlobalization and its runtimeconfig
- /// sets System.Globalization.PredefinedCulturesOnly to false, so it genuinely needs ICU.
- ///
- /// MaxSoVersion bounds the dlopen fallback used when ldconfig cannot answer. It is per library
- /// because the SONAME digit is: libdeflate is .so.0 and libargon2 is .so.1 on the same machine,
- /// while ICU tracks its own release train and was .so.74 on Ubuntu 24.04, .so.76 on Alpine and
- /// .so.77 on Fedora. A single small bound silently reports ICU missing when it is installed.
+ /// Native libraries the server needs from the system on Linux, and the SONAME range to accept
+ /// for each. Rationale and per-distro package names: dev-docs/platform-prerequisites.md.
///
- private static readonly (string Name, int MaxSoVersion)[] _linuxLibraries =
+ private static readonly (string Name, int MinSoVersion, int MaxSoVersion)[] _linuxLibraries =
[
- ("libicuuc", 99),
- ("libdeflate", 9),
- ("libargon2", 9)
+ ("libicuuc", 60, 120),
+ ("libicui18n", 60, 120),
+ ("libdeflate", 0, 9),
+ ("libargon2", 0, 9)
];
private static List CheckLinux(PlatformInfo platform)
{
- // Ask whether the loader can find each library rather than whether a named package is
- // installed. Package names were why the -dev packages were mandated, and no hardcoded name
- // works for ICU anyway: its apt package is release-specific (libicu72, libicu74, ...).
- // ldconfig -p is the loader's own cache, so matching on the "libfoo.so" prefix covers
- // libdeflate.so.0, libargon2.so.1 and libicuuc.so.76 alike.
- //
- // It is only ever a fast *positive* signal. musl's ldconfig exits 0 while producing no
- // usable cache, so trusting a negative from it reports every library missing on Alpine even
- // when all of them are installed. A cache can also be stale or omit LD_LIBRARY_PATH.
- // Anything it does not vouch for gets dlopen'd for real before being called missing.
- var ldResult = ProcessRunner.RunCaptured("ldconfig", "-p");
- var cache = ldResult.Success ? ldResult.StandardOutput : null;
-
var results = new List();
var missing = new List();
- foreach (var (name, maxSoVersion) in _linuxLibraries)
+ foreach (var (name, minSoVersion, maxSoVersion) in _linuxLibraries)
{
- var found = cache?.Contains($"{name}.so", StringComparison.Ordinal) == true ||
- CanLoad(name, maxSoVersion);
+ var found = CanLoad(name, minSoVersion, maxSoVersion);
if (!found)
{
@@ -236,6 +213,19 @@ public static class NativeLibraryChecker
});
}
+ var hasTimeZoneData = HasTimeZoneData();
+ if (!hasTimeZoneData)
+ {
+ missing.Add("tzdata");
+ }
+
+ results.Add(new PrerequisiteResult
+ {
+ Name = "tzdata",
+ Passed = hasTimeZoneData,
+ Details = hasTimeZoneData ? "Found" : "Not found — every zone except UTC will throw"
+ });
+
if (missing.Count == 0)
{
return results;
@@ -258,7 +248,7 @@ public static class NativeLibraryChecker
Name = "Install all missing",
Passed = false,
IsWarning = true,
- Details = "Install the runtime libraries. The -dev/-devel packages are not required:",
+ Details = "Install the missing dependencies. The -dev/-devel packages are not required:",
InstallCommand = BuildInstallCommand(platform, missing)
});
@@ -266,18 +256,37 @@ public static class NativeLibraryChecker
}
///
- /// Asks the loader directly, for when ldconfig cannot answer. Mirrors the binding packages'
- /// own probing: the unversioned name first, then libfoo.so.N descending. Bare names go through
- /// the full loader search path, so LD_LIBRARY_PATH and /etc/ld.so.conf.d still apply.
+ /// tzdata is data, not a library, so no loader probe finds it. Asking the runtime rather than
+ /// stat'ing a path keeps TZDIR honoured, and the count is still accurate under
+ /// InvariantGlobalization, which this tool runs with — only display names degrade there.
///
- private static bool CanLoad(string library, int maxSoVersion)
+ private static bool HasTimeZoneData()
+ {
+ try
+ {
+ return TimeZoneInfo.GetSystemTimeZones().Count > 1;
+ }
+ catch
+ {
+ return false;
+ }
+ }
+
+ ///
+ /// Asks the loader directly rather than querying a package database or scanning ldconfig's
+ /// cache, both of which answer a different question and can disagree with what dlopen will do.
+ /// Mirrors the binding packages' own probing: the unversioned name first, then libfoo.so.N
+ /// descending. Bare names go through the full loader search path, so LD_LIBRARY_PATH and
+ /// /etc/ld.so.conf.d still apply.
+ ///
+ private static bool CanLoad(string library, int minSoVersion, int maxSoVersion)
{
if (TryLoadAndFree($"{library}.so"))
{
return true;
}
- for (var soVersion = maxSoVersion; soVersion >= 0; soVersion--)
+ for (var soVersion = maxSoVersion; soVersion >= minSoVersion; soVersion--)
{
if (TryLoadAndFree($"{library}.so.{soVersion}"))
{
@@ -305,14 +314,17 @@ public static class NativeLibraryChecker
{
case PackageManager.Apt:
{
+ // Distinct because the two ICU libraries resolve to the same package, and
+ // ResolveAptIcuPackage shells out, so it is memoized rather than called per name.
var packages = missing.Select(
library => library switch
{
"libdeflate" => "libdeflate0",
"libargon2" => "libargon2-1",
- _ => ResolveAptIcuPackage()
+ "tzdata" => "tzdata",
+ _ => _aptIcuPackage ??= ResolveAptIcuPackage()
}
- );
+ ).Distinct();
return $"sudo apt-get install -y {string.Join(' ', packages)}";
}
@@ -323,9 +335,10 @@ public static class NativeLibraryChecker
{
"libdeflate" => "libdeflate",
"libargon2" => "libargon2",
+ "tzdata" => "tzdata",
_ => "libicu"
}
- );
+ ).Distinct();
return $"sudo dnf install -y {string.Join(' ', packages)}";
}
@@ -334,6 +347,8 @@ public static class NativeLibraryChecker
}
}
+ private static string _aptIcuPackage;
+
///
/// ICU's apt package carries the ABI version in its name and there is no stable alias, so ask
/// apt which one this release actually ships instead of printing a name that rots.
diff --git a/README.md b/README.md
index 1b76ce804..2321fe8e3 100644
--- a/README.md
+++ b/README.md
@@ -87,21 +87,27 @@ dnf install -y dnf-plugins-core
dnf config-manager --set-enabled crb
dnf install -y epel-release
# Prerequisites
-dnf install -y findutils libicu libdeflate libargon2
+dnf install -y findutils libicu libdeflate libargon2 tzdata
```
### Ubuntu, Debian, etc
```shell
apt-get update -y
-apt-get install -y libicu-dev libdeflate0 libargon2-1
+# The ICU runtime package carries the ABI version in its name (libicu74, libicu76, …) and has no
+# stable alias, so match it by pattern rather than pinning a release-specific name.
+apt-get install -y '^libicu[0-9]+$' libdeflate0 libargon2-1 tzdata
```
-Only the runtime libraries are needed — the `-dev`/`-devel` packages are not. ICU is the exception
-on Debian and Ubuntu, where the runtime package carries the ABI version in its name (`libicu74`,
-`libicu76`, …) and there is no stable alias, so `libicu-dev` is the version-independent way to pull
-it in. Run `./build-tool --check-prereqs` to print the exact packages your release needs.
+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 no longer listed because ZstdNet bundles `libzstd` for every platform.
+`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](dev-docs/platform-prerequisites.md)
+for what each dependency is for and what breaks without it.
## OSX Requirements
```shell
diff --git a/dev-docs/platform-prerequisites.md b/dev-docs/platform-prerequisites.md
new file mode 100644
index 000000000..3e76d3b47
--- /dev/null
+++ b/dev-docs/platform-prerequisites.md
@@ -0,0 +1,159 @@
+# Platform Prerequisites
+
+OS-level dependencies ModernUO needs at runtime, why each one is required, and what breaks without
+it. This page is about software packages, not hardware sizing.
+
+Run `./build-tool --check-prereqs` from the repository root to check the current machine. It prints
+the exact install command for the detected distribution.
+
+## What is required
+
+| Dependency | Platform | Why |
+|---|---|---|
+| .NET 10 Runtime | all | — |
+| ICU (`libicuuc`, `libicui18n`) | Linux, macOS | The runtime refuses to start without it; see below |
+| tzdata | Linux | Time zone lookups; see below |
+| `libdeflate` | all | `LibDeflate.Bindings` |
+| `libargon2` | all | `Argon2.Bindings` (password hashing) |
+| VC++ Redistributable v14 | Windows | Native bindings |
+
+Not required, despite appearances:
+
+- **zstd** — `ZstdNet` bundles `libzstd` for every RID.
+- **liburing** — `IORingGroup` issues `io_uring` syscalls directly. It imports only `libc`,
+ `libSystem.dylib`, `kernel32.dll`, `kernelbase.dll` and `ws2_32.dll`.
+- **`-dev` / `-devel` packages** — see "Runtime packages only" below.
+
+## Install
+
+```sh
+# Debian / Ubuntu (ICU has no stable package alias, so match it by pattern)
+sudo apt-get install -y '^libicu[0-9]+$' libdeflate0 libargon2-1 tzdata
+
+# Fedora / RHEL
+sudo dnf install -y libdeflate libargon2 libicu tzdata
+
+# Alpine
+apk add --no-cache libdeflate argon2-libs icu-libs tzdata
+
+# macOS
+brew install icu4c libdeflate argon2
+```
+
+CentOS additionally needs EPEL and CRB:
+
+```sh
+sudo dnf install -y epel-release epel-next-release && sudo dnf config-manager --set-enabled crb
+```
+
+## Runtime packages only
+
+Only the runtime packages are needed. The `-dev`/`-devel` packages are **not** required.
+
+They used to be, because .NET's `DllImport` probing looks for the unversioned `libfoo.so`, and on
+Linux that bare symlink ships only in the development package. The runtime package ships the
+versioned SONAME (`libdeflate.so.0`, `libargon2.so.1`). The binding packages now probe the versioned
+names as well, so the runtime package is sufficient.
+
+Anything still documenting `libicu-dev` or `libdeflate-dev` as a requirement is out of date.
+
+## ICU
+
+`Directory.Build.props` sets `InvariantGlobalization=false`, so ICU is mandatory. Without it the
+runtime does **not** throw — it `FailFast`s:
+
+```
+Couldn't find a valid ICU package installed on the system. Please install libicu (or icu-libs)
+using your package manager and try again.
+```
+
+That is `SIGABRT` (exit 134) and it cannot be caught. Note the process **starts cleanly and aborts
+later**, at whatever line first touches a culture, so the crash rarely points at the cause.
+
+### Why invariant mode is not an option
+
+`InvariantGlobalization=true` would remove the ICU dependency, but it changes behaviour in ways that
+corrupt data silently. Measured on .NET 10 with the repository's settings:
+
+| Behaviour | With ICU | Invariant mode |
+|---|---|---|
+| `new CultureInfo("de-DE")` | real culture | succeeds, returns invariant data |
+| de-DE decimal separator | `,` | `.` |
+| `1234.5` as de-DE | `1.234,5` | `1,234.5` |
+| `string.Compare("a", "B", InvariantCulture)` | `-1` (linguistic) | `31` (ordinal) |
+| sort `[b, A, a, B]` | `a, A, b, B` | `A, B, a, b` |
+| `FindSystemTimeZoneById("Eastern Standard Time")` on Linux | resolves | `TimeZoneNotFoundException` |
+| UTF-8 round-trip of non-ASCII | unaffected | unaffected |
+
+The dangerous row is the first. Because `Directory.Build.props` also sets
+`PredefinedCulturesOnly=false`, constructing a culture in invariant mode **succeeds** instead of
+throwing `CultureNotFoundException`, and hands back an object populated with invariant data. Number
+parsing and formatting then produce wrong values with no error, and culture-sensitive sort order
+silently becomes ordinal.
+
+Encoding is not affected — UTF-8 round-trips correctly in both modes.
+
+### Version floor
+
+The runtime accepts `libicuuc.so.60` and above (`MinICUVersion` in `pal_icushim.c`). The prerequisite
+checker enforces the same floor, so a host carrying only an older ICU is reported missing rather than
+passing and then aborting at startup. RHEL/CentOS 7 ships ICU 50 and is affected.
+
+ICU tracks its own release train, so the SONAME digit varies widely by distribution — `.so.74` on
+Ubuntu 24.04, `.so.76` on Alpine, `.so.77` on Fedora, `.so.78` on openSUSE. There is no stable
+package alias on Debian and Ubuntu, which is why the checker resolves the name via `apt-cache`
+instead of hardcoding one.
+
+Only `libicuuc` and `libicui18n` are used; those are the two names
+`libSystem.Globalization.Native.so` loads. `libicudata` arrives as a dependency of `libicuuc`, and
+`libicuio`/`libicutu`/`libicutest` are never referenced. Every distribution ships all of them in a
+single package, so installing ICU at all satisfies both.
+
+## tzdata
+
+The event scheduler resolves configured zone IDs through `TimeZoneInfo`, which reads
+`/usr/share/zoneinfo` on Linux. This is separate from ICU: it is data, not a library, so no loader
+probe finds it, and slim container images routinely omit it.
+
+Without tzdata every lookup except `UTC` throws:
+
+```
+TimeZoneNotFoundException: The time zone ID 'America/New_York' was not found on the local computer.
+```
+
+`TimeZoneInfo.GetSystemTimeZones()` returns 1 entry instead of ~419, and `TimeZoneInfo.Local` falls
+back to UTC.
+
+### There is no per-zone subset
+
+Distributions do not package individual zones — it is one `tzdata` package, about 2 MB installed for
+the full set. Subsetting is not worth pursuing.
+
+The one split that does exist is **`tzdata-legacy`** on Debian 12 and Ubuntu 24.04, which carries the
+deprecated aliases. With plain `tzdata` alone:
+
+| Zone ID | `tzdata` | `tzdata-legacy` |
+|---|---|---|
+| `America/New_York` | present | — |
+| `Europe/Kyiv` | present | — |
+| `EST5EDT` | present | — |
+| `US/Eastern` | **missing** | present |
+| `Asia/Calcutta` | **missing** | present |
+
+So a shard configured with a legacy alias such as `US/Eastern` throws on a current Debian or Ubuntu
+even though tzdata is installed. Either install `tzdata-legacy` or switch the configured value to the
+canonical ID (`America/New_York`, `Asia/Kolkata`).
+
+`TZDIR` is honoured if the data lives somewhere non-standard.
+
+## How the check works
+
+`--check-prereqs` asks the loader directly — `NativeLibrary.TryLoad` on the unversioned name, then
+`libfoo.so.N` descending through the accepted range.
+
+It deliberately does not consult a package database or `ldconfig -p`. Both answer a different
+question than "will `dlopen` succeed":
+
+- Package queries need a hardcoded name, which does not exist for ICU.
+- `ldconfig`'s cache can be stale, omits `LD_LIBRARY_PATH`, and carries no version information to
+ enforce the ICU floor against. On musl it exits successfully while producing nothing usable.