Note: if using modern Ubuntu or Debian 32-bit, first do: sudo apt-get install lib32gcc1

wget -c http://storefront.steampowered.com/download/hldsupdatetool.bin || exit
chmod +x hldsupdatetool.bin || exit
./hldsupdatetool.bin || exit
 
test -e go || cat <<EOL > go
export RDTSC_FREQUENCY=2500.000000
cd left4dead2
./srcds_run l4d -autoupdate +hostport 27015 +ip 0.0.0.0 +exec server.cfg
EOL
chmod +x go
 
mkdir -p left4dead2/left4dead2/cfg
ln -s left4dead2/left4dead2/cfg/server.cfg .
ln -s left4dead2/left4dead2/motd.txt .
ln -s left4dead2/left4dead2/host.txt .
 
cat <<EOL > server.cfg
hostname "ZOMBONI 9003"
rcon_password "XXXXX"
z_difficulty "advanced"
sv_region 0
sv_gametypes "coop, versus, survival, scavenge"
sv_allow_lobby_connect_only 0
EOL
 
echo './steam -command update -game left4dead2 -dir .' > update
chmod +x update
 
./update ; ./update

Get steam:

wget http://storefront.steampowered.com/download/hldsupdatetool.bin
chmod +x hldsupdatetool.bin
./hldsupdatetool.bin

Install:

./steam -command update -game left4dead2 -dir .

Three useful files:

left4dead2/left4dead2/cfg/server.cfg -- Server config (doesn't exist by default)
left4dead2/left4dead2/motd.txt -- Message of the day (either text, or a URL to a page)
left4dead2/left4dead2/host.txt -- Banner for the server (a URL to HTML that fills banner-like dimensions)

Launch script:

export RDTSC_FREQUENCY=2500.000000
cd left4dead2
./srcds_run l4d -autoupdate +hostport 28015 +ip 0.0.0.0 +exec server.cfg

Sample server.cfg (locks the server down to so it can only be requested directly (see below)):

hostname "ZOMBONI 9003"
rcon_password "XXXXX"
z_difficulty "advanced"
sv_region 0
sv_gametypes "coop, versus, survival, scavenge"
sv_allow_lobby_connect_only 0

By default, the server will be open to all comers. The "sv_allow_lobby_connect_only 0" in the server config above prevents this. To allow YOU to use it, use the "mm_dedicated_force_servers" console command before hitting "go" in the game lobby. This command supports IP addresses only (no hostnames). Example:

mm_dedicated_force_servers 100.102.104.106:27015

To avoid having to type this, you can add a key bind to your game to set it. Edit "steamapps\common\left 4 dead 2\left4dead2\cfg\config.cfg" and add the line:

bind "F12" "mm_dedicated_force_servers 100.102.104.106:27015"

Then, in game, just hit F12 any time to make the game use your server.

Script to update the addons list when new addons are introduced ("remake-addonlist.pl"):

#!/usr/bin/perl
 
use strict;
 
my $addonlist = "left4dead2/left4dead2/addonlist.txt";
my $addondir  = "left4dead2/left4dead2/addons";
 
rename($addonlist,"$addonlist.old");
open FP, "> $addonlist" or die "$addonlist: $!\n";
 
print FP <<EOL;
"AddonList"
{
EOL
 
my $n=0;
 
print "Writing addon list...\n";
for (glob("$addondir/*.vpk")) {
        s#.*/##;
        print FP qq(  "$_" "1"\n);
        print "- $_\n";
        $n++;
}
 
print FP "}\n";
close FP;
 
print "Wrote $n addons.\n";