ReHLDS is a reverse-engineered, bug-fixed rewrite of the Half-Life dedicated server engine, maintained by the rehlds GitHub organisation. It is a drop-in replacement for the engine binary: same directory layout, same cvars, same mods. What you get is a large pile of fixed engine bugs, real anti-exploit protections against the classic HL crash packets, faster networking, and cvars that plain HLDS simply does not have. There is no serious reason to run stock HLDS on a public server in 2026.

1. Start from a working HLDS install

ReHLDS replaces files inside an existing App 90 install — it is not a full server. If you do not have one yet, do the SteamCMD install first and make sure the vanilla server boots to a map.

2. Get the right build

Download the latest ReHLDS release archive from the project's GitHub releases page. The archive contains both platforms; you want the Linux directory. Do not mix a Linux engine_i486.so with Windows swds.dll files from a different release — engine and Metamod ABI expectations are tied to the build.

The Linux files that matter:

engine_i486.so
hlds_linux        (the launcher ReHLDS ships)
libstdc++.so.6    (only if the archive contains one — usually you keep the system one)

3. Back up, then copy

cd /home/steam/hlds
cp engine_i486.so engine_i486.so.valve.bak
cp hlds_linux hlds_linux.valve.bak
cp /path/to/rehlds/engine_i486.so ./engine_i486.so
cp /path/to/rehlds/hlds_linux ./hlds_linux
chmod +x hlds_linux hlds_run

Both files go in the server root (next to hlds_run), never inside cstrike/. Copying engine_i486.so into cstrike/ is a classic mistake — the server keeps running the Valve engine and you spend an hour wondering why version shows no ReHLDS version: line.

4. Start the server

cd /home/steam/hlds
./hlds_run -game cstrike -strictportbind -ip 0.0.0.0 -port 27015 \
  +map de_dust2 +maxplayers 20 +sv_lan 0

The startup output looks the same as Valve's (Protocol version, Exe version and Exe build lines) and does not name ReHLDS, so do not judge by it. The check in the next step is the one that counts.

5. Verify it is actually running

In the server console:

version

ReHLDS prints a line starting ReHLDS version: with its version number, followed by Build date and Build from lines. A stock HLDS prints only the Protocol version, Exe version and Exe build lines. That single command is the whole verification — do not trust the file timestamp, trust the command.

6. ReHLDS-specific cvars worth setting

Put these in cstrike/server.cfg. They are the reason people install ReHLDS in the first place:

// optional behaviour fixes, not packet filters:
// stops fast leg animation on players with attached models (can lag at low cl_updaterate)
sv_rehlds_attachedentities_playeranimationspeed_fix 1
// per-client game clock, reduces lag when one map runs a long time
sv_rehlds_local_gametime 1
// do not send mapcycle.txt to clients (they never use it; this is the default)
sv_rehlds_send_mapcycle 0
// send in-game downloads in full 1024-byte fragments, ignoring the client's cl_dlmax
sv_rehlds_force_dlmax 1
// hardening
sv_filterban 1
sv_rcon_maxfailures 5
sv_rcon_minfailures 5
sv_rcon_minfailuretime 30

Enable them one at a time, restart, and watch the log. Some hardening cvars interact badly with old plugins that send hand-built messages — if the server starts crashing right after you turn a batch on, see crash after enabling ReHLDS security cvars.

7. Rebuild the rest of the stack in order

ReHLDS on its own is only the engine. The order that works:

1. ReHLDS (engine) — you are here.
2. ReGameDLL_CS — replaces cstrike/dlls/cs.so, the game logic.
3. Metamod-r — the plugin loader, pointed at from liblist.gam.
4. AMX Mod X — loaded by Metamod.
5. ReAPI — only useful once ReHLDS and ReGameDLL are both in place.

Do not install ReAPI before ReGameDLL. ReAPI hooks functions that only exist in ReGameDLL; without it the module refuses to load or the server dies at map start.

Common errors

• version shows no ReHLDS version: line — the engine was not replaced. You copied engine_i486.so to the wrong directory, or you are launching a different hlds_linux (check with ps aux | grep hlds and look at the path).
• Segmentation fault immediately at startup — mismatched binaries: a 64-bit build of something in the chain, or a Metamod version that predates the ReHLDS API. Confirm with file engine_i486.so; it must say ELF 32-bit LSB shared object, Intel 80386. If it says x86-64, you downloaded the wrong archive.
• Host_Error: Couldn't get DLL API from ./cstrike/dlls/cs.so — your ReGameDLL build is older or newer than the ReHLDS engine's expected interface. Update both to the current releases; see ReGameDLL/ReHLDS incompatibility.
• Metamod plugins show bad load after the switch — you are on classic Metamod with an old ABI. Move to Metamod-r, or read the bad load fix.

Rolling back

Because you backed up the originals, rollback is two commands:

cd /home/steam/hlds
cp engine_i486.so.valve.bak engine_i486.so
cp hlds_linux.valve.bak hlds_linux

Restart, run version, and confirm the ReHLDS version: line is gone. Keep those .bak files — they are the only trivially available copy of the Valve engine once you have overwritten it, short of re-running app_update 90 validate (which, usefully, also restores them).

Verification checklist

• version prints a ReHLDS version: line.
• The server reaches a map and accepts a client connection.
• meta list (if Metamod is installed) shows every plugin as RUN.
• The log has no repeating warnings on map change.

If all four hold, you are on ReHLDS. Next: the full modern stack, or compile it yourself with the Docker build guide.