Unable to load extension "accelerator.ext": bin/libstdc++.so.6: version `GLIBCXX_3.4.21' not found

[SefoNotasi]

Hi! I’m trying to use the latest Accelerator version on my Linux L4D2 server
(Ubuntu 24.04 LTS, fresh install), but the extension fails to load on startup:

L 12/06/2025 - 00:26:43: [SM] Unable to load extension "accelerator.ext": bin/libstdc++.so.6: version `GLIBCXX_3.4.21' not found (required by /home/steam/server/left4dead2/addons/sourcemod/extensions/accelerator.ext.so)

I searched thread on AlliedModders and found old messages where people had this issue in 2019,
and they fixed it using the CentOS6 build you posted.
I tried that build as well and it loads correctly, but then Crash Reports say
that I am using an outdated Accelerator version.

So my question is:
What should I do to run the latest Accelerator version on Linux (Ubuntu)?
Is there something I need to install or configure on my system to make it load correctly?

[Kenzzer]

Do not download older builds, stay on latest released binaries. If it fails to load, just open an issue here like you've done and we will attempt to resolve it.

Anyways the issue you're currently facing is two-faced :
First, the version of libstdc++ that valve ships with the l4d2 is too old. I invite you to simply delete the file and let the version from your system to be loaded instead.

The second problem, which you haven't encountered but soon will, even by deleting that file the system is going to load libstdc++ too late. We need to preload that library before booting the server.

Make yourself a custom start script and do the following

#!/bin/bash
export LD_PRELOAD="/path/to/libstdc"
exec ./srcds_run "$@"

Replace /path/to with the actual path to your system's libstdc++.

I realise this might be over your head if you're not super familiar with linux, so here's a quick guide for you and everybody else attempting to load Accelerator on L4D2 servers.

Delete libstdc++ from your server installation

For stability and support reasons, valve ships the srcds with its own libstdc++. This is problematic because it will prevent our extension from working properly.

Navigate to where your server is installed and run the following command
find ./bin -type f -name "libstdc++*" 2>/dev/null

You should get an output similar to this
./bin/libstdc++.so.6
or
./bin/linux64/libstdc++.so.6

Delete all files that are found.

(Optional) Add the 32bits version of libstdc++ to your system

If you're running the 32bits version of the srcds and using a recent linux distro, then there's a good chance the 32bits version of libstdc++ is missing from your system. Let's download it right now by performing the following commands

sudo dpkg --add-architecture i386
sudo apt update
sudo apt install libstdc++6:i386

Make a custom launch script for your server

Now that we've deleted the libstdc++ provided by valve, we want the libstdc++ of our system to be loaded instead. Let's locate the libstdc++ by running the following command :

find /usr/lib /usr/lib64 /lib /lib64 -type f -name "libstdc++*" 2>/dev/null

This should produce an output similar to this :

/usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.30
/usr/lib/i386-linux-gnu/libstdc++.so.6.0.30

If you're running the 64 bits version of the srcds, copy the path with the '64' if you're running the 32 bits version then copy the other path.

DO NOT COPY THE PATHS FROM THIS POST, ACTUALLY RUN THE COMMAND

Now that we know where our libstdc++ is, let's create a custom launch script called custom_srcds_run.

#!/bin/bash
export LD_PRELOAD="/path/to/libstdc++.so.x.x.x"
exec ./srcds_run "$@"

(Replace srcds_run by srcds64_run if running 64 bits)

Now launch the server the same way you would normally

./custom_srcds_run -game <game> +map <map> +maxplayers X