left4me/docs/l4d2-server-cvar-reference.md

# L4D2 server cvar reference

Working notes from the 2026-05 research session on best-practice
L4D2 dedicated server settings. Sources cited inline; some findings
verified empirically on the `left4.me` Trixie test server (kernel
6.12.86). This is reference material, not a settled design.

## Quick lookup

| Topic | Recommended |
|---|---|
| Tickrate (stock) | 30 |
| Tickrate (competitive) | 100, requires Tickrate Enabler plugin |
| `sv_pure` | `2` (strict), or `0`/`1` for modded servers |
| `sv_cheats` | `0` (set to 1 only on private practice servers; disables VAC) |
| `sv_consistency` | `0` (allow custom campaigns) or `1` (strict for competitive) |
| `sv_alltalk` | `0` (no cross-team voice), `1` for casual / fun servers |
| `sv_lan` | `0` (internet server) |
| `sv_voiceenable` | `1` |
| `nb_update_frequency` | `0.033` (safe, no plugin), `0.014` with the SM fix plugin. **Cheat-protected — must be set via `sm_cvar`.** |
| `fps_max` | `64` for 30-tick, `0` (uncapped) for higher ticks |

## Network rates

L4D2 default tickrate is **30**. Rates above the corresponding
ceiling are ignored without the
[Tickrate Enabler plugin](https://github.com/SirPlease/Server4Dead-Project/tree/master/Tickrate%20Enabler).

Rule of thumb: `sv_maxrate = tickrate × 1000`.

### 30-tick (stock)

```
sv_minrate              30000
sv_maxrate              30000
sv_mincmdrate           30
sv_maxcmdrate           30
sv_minupdaterate        30
sv_maxupdaterate        30
net_splitpacket_maxrate 30000
fps_max                 64
```

### 60-tick (requires Tickrate Enabler)

```
sv_minrate              60000
sv_maxrate              60000
sv_mincmdrate           60
sv_maxcmdrate           60
sv_minupdaterate        60
sv_maxupdaterate        60
net_splitpacket_maxrate 60000
fps_max                 128
```

### 100-tick (competitive, requires Tickrate Enabler)

```
sv_minrate              100000
sv_maxrate              100000
sv_mincmdrate           100
sv_maxcmdrate           100
sv_minupdaterate        100
sv_maxupdaterate        100
net_splitpacket_maxrate 100000
fps_max                 0
```

### sv_min*rate vs. sv_max*rate

- Locking `min == max` (competitive servers do this) ensures every
  client sends at the tickrate exactly. Strict — kicks clients
  that dip below.
- Leaving a range (e.g. `min=10, max=30` on a 30-tick public
  server) tolerates clients on weak connections or loaded CPUs.
- Setting `sv_mincmdrate=0` means *no enforced minimum* — clients
  could send as few as 1-2 cmds/sec. Bad. Pick a floor that's
  playable (~10 minimum).

## Cheat-protected cvars and `sm_cvar`

Several gameplay-affecting cvars are flagged as "cheat" in L4D2 and
**cannot be set via `server.cfg` unless `sv_cheats 1`** — which
disables VAC and gates achievements. Trying to set them from cfg
silently fails (the value stays at default).

To set them on a real (VAC-protected) server: install SourceMod and
use `sm_cvar <name> <value>` instead of `<name> <value>`. SourceMod
bypasses the cheat protection for *server-side cvar writes only*
(does not grant cheat commands to players).

Cheat-protected cvars worth knowing:
- `nb_update_frequency` — common-infected pathing/state update
  rate (see below).
- `director_*` — most director cvars (AI difficulty, panic events,
  pacing).
- `z_*` — most zombie-behavior cvars.

`sm_cvar` writes go in `cfg/sourcemod/sourcemod.cfg` (auto-execed
by SM on map change) or in any cfg under `cfg/sourcemod/`. SM
re-applies these on every map change — important because
cheat-protected cvars *reset to defaults on map change* even
within the same server session.

## `nb_update_frequency`

Controls how often common infected and witches recalculate their
pathfinding and state. Default `0.1` (10 Hz), independent of
server tickrate.

| Value | Effect |
|---|---|
| `0.1` (default) | Common-infected look choppy regardless of tickrate |
| `0.033` | ~30 Hz updates; smooth, safe without plugin |
| `0.024` | Lowest "safe" without plugin per community testing |
| `0.014` | ~71 Hz; clients with `cl_interp 0` see jittery commons unless the [nb_update_frequency fix plugin](https://forums.alliedmods.net/showthread.php?t=344019) is installed |

Set via `sm_cvar nb_update_frequency 0.033` in
`cfg/sourcemod/sourcemod.cfg` (or any sm-auto-execed cfg). Without
SourceMod, you cannot reliably set this on a VAC-protected server.

If commons still look choppy after lowering `nb_update_frequency`,
try `sm_cvar z_resolve_zombie_collision_multiplier 0.6` (default
`0.25`) — helps commons unstick from each other. Cheat-protected,
same `sm_cvar` mechanism.

## Cvars that DO NOT exist in L4D2 (despite some guides claiming otherwise)

These come up in older guides or are inherited from other Source
games but don't actually exist in L4D2's command set. Verified by
RCON `<cmd>` returning "unknown command":

- `net_maxcleartime` — CSGO/CS:S only.
- `z_resolve_zombie_collision_multiplier` — confirmed unknown in
  current L4D2 builds (verified via RCON 2026-05-14). Some
  community guides list it; it's not in the binary.

If a guide tells you to set one of these in L4D2, the guide is
wrong or out of date.

## Security and integrity

```
sv_cheats       0
sv_pure         2             # force Steam-only files (strictest)
sv_consistency  1             # enforce file hashes for critical files
                              # (set 0 if hosting custom campaigns)
sv_lan          0             # internet server
```

Launch the server with `-secure` to enable VAC. `sv_cheats 1`
requires `-insecure` (no VAC) — only acceptable on private
practice servers.

`sv_pure 2` breaks many workshop maps/mods. Use `sv_pure 0` or `1`
for modded servers.

## Player limits

```
# Co-op / Scavenge
sv_maxplayers           4
sv_visiblemaxplayers    4

# Versus
sv_maxplayers           8
sv_visiblemaxplayers    8
```

## Voice

```
sv_voiceenable  1
sv_alltalk      0   # 1 = cross-team voice (casual / fun servers)
```

## Recommended plugins (SourceMod ecosystem)

| Plugin | Purpose |
|---|---|
| MetaMod:Source + SourceMod | Required foundation for most of the below |
| [Tickrate Enabler](https://github.com/SirPlease/Server4Dead-Project/tree/master/Tickrate%20Enabler) | Unlock >30 tick servers |
| [Little Anti-Cheat](https://github.com/J-Tanzanite/Little-Anti-Cheat) | Aimbot / angle-cheat detection |
| SMAC | Secondary AC layer (older but still works) |
| [ZoneMod](https://github.com/SirPlease/L4D2-Competitive-Rework) | Competitive Versus ruleset (full bundle: ZoneMod + MatchMode + Confogl-style plugins) |
| `l4d2_TKStopper` | Teamkill / griefing control |
| `l4d_sb_fix` | Survivor bot behavior fixes |
| [nb_update_frequency fix](https://forums.alliedmods.net/showthread.php?t=344019) | Eliminates client-side jitter at very low `nb_update_frequency` values |

## MetaMod:Source / SourceMod versioning

- Stable branches are pinned in URL paths: `1.10`, `1.11`, `1.12`,
  etc. There is no "latest stable" alias URL — you pick the
  branch.
- Within a branch, the `mmsource-latest-linux` and
  `sourcemod-latest-linux` text files contain the current build's
  filename, e.g. `mmsource-1.12.0-git1219-linux.tar.gz`. Curl the
  pointer file, then curl the actual tarball.
- AM bumps stable every ~2-3 years. When 1.13 (or later) is
  declared stable, update the `MM_BRANCH=1.12` / `SM_BRANCH=1.12`
  pins in the seeded Sourcemod overlay script.
- L4D2 has no special branch — it uses whatever the current
  stable supports. L4D2's engine is so stable that SM 1.11 and
  1.12 both work.

Watch for stable announcements at
[Metamod:Source news](https://www.sourcemm.net/) and
[SourceMod releases](https://github.com/alliedmodders/sourcemod/releases).

## Empirically-verified kernel quirk (relevant if you tweak the helpers)

Idmapped bind mounts on kernel 6.12 (Trixie) **do** propagate
through plain `mount --bind` re-binds. Verified end-to-end on
`left4.me` during the 2026-05-15 build-time-idmap refactor: a
sandbox process inside a re-bound idmapped mount can write files,
and those writes land on disk with the idmap-translated uid.

This contradicts some published claims (including a generic
research-agent summary) that idmaps don't propagate through plain
re-bind on this kernel. Our use case is `mount --bind --map-users
src staging` → systemd-run with `BindPaths=staging:/overlay` (a
plain re-bind into the unit's namespace). It works.

The `--map-users <a>:<b>:<count>` direction is **on-disk uid
first**, then in-mount uid. The util-linux man page calls these
`<inner>:<outer>` which is confusing — `<inner>` means "the
filesystem's native uid" (on disk) and `<outer>` means "the uid
exposed outward through the mount." Empirically verified; do not
trust the man page's word choice.

## Launch parameters (reference)

Typical srcds invocation:

```
./srcds_run -console -game left4dead2 -secure -autoupdate \
    +maxplayers 8 -port 27015 +exec server.cfg +log on
```

- `-secure` enables VAC. Don't run public servers without it.
- `-autoupdate` keeps the server patched automatically.
- `+exec server.cfg` runs your config on startup.
- `-tickrate <N>` sets the engine tickrate (requires Tickrate
  Enabler for `N > 30`).

## Sources

Primary references used for the recommendations above:

- [L4D2-Competitive-Rework server.cfg](https://github.com/SirPlease/L4D2-Competitive-Rework/blob/master/cfg/server.cfg)
- [L4D2 Dedicated Server Guide (Steam Community)](https://steamcommunity.com/sharedfiles/filedetails/?id=276173458)
- [L4D2 Dedicated Server Network Tweaks (Steam Discussions)](https://steamcommunity.com/app/550/discussions/1/1839063537784156851/)
- [SirPlease/Server4Dead-Project — Tickrate Enabler](https://github.com/SirPlease/Server4Dead-Project/tree/master/Tickrate%20Enabler)
- [Valve Developer Community — L4D2 console commands](https://developer.valvesoftware.com/wiki/List_of_Left_4_Dead_2_console_commands_and_variables)
- [AlliedModders — nb_update_frequency fix (Experimental)](https://forums.alliedmods.net/showthread.php?t=344019)
- [Source Multiplayer Networking — Valve Developer Community](https://developer.valvesoftware.com/wiki/Source_Multiplayer_Networking)
- [Required Versions (SourceMod wiki)](https://wiki.alliedmods.net/Required_Versions_(SourceMod))
- [MetaMod:Source news](https://www.sourcemm.net/)