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Half-Life: Decay Installation for SP and Online Co-op Guide
By Miyumi
This guide aims to provide an updated (2015) guide on how to successfully install and play Half-Life: Decay in Singleplayer and Online Co-op on the PC.
Most of the guides I encountered were very informative but they were published back in 2010 with some dating back 2008, since then, the Steam Client had undergone several updates and changes that makes the old guides outdated.

Image from Wikipedia[en.wikipedia.org]

Half-Life: Decay[half-life.wikia.com] is a first-person action shooter by Gearbox Software and Valve and serves as the third official expansion to the critically acclaimed 1998 game Half-Life. Unlike its predecessors (or even the main game), Half-Life: Decay is exclusive to the PS2 and the first in the Half-Life franchise to be designed for co-operative play.

Although Gearbox Software successfully created a port of the game for a PC release, it never saw the light of day "due to powers beyond Gearbox's control" thus prompting some dedicated fans to take matters in their own hands. A Fan made port was released in 2008 and is made available at Half-Life Creations Website[decay.half-lifecreations.com]

Patrick Deupree, a developer and member of the Gearbox team that made Half-Life: Decay, had this to say:
Originally posted by Patrick Deupree:
I work for Gearbox and did most of the coding for the Decay work we did on the PS2. First I'd like to say that there is no interest or desire on our part to fox this project. Everyone here thinks it would be great to see this ported to Source.

We even had a port of the game ready on HL1 for the PC, but due to powers beyond our control, were unable to release it at the time. So it's always been of interest to us to see Decay make it to the PC since, as someone else here has mentioned, it does deliver a part of the Half-Life storyline so it's always been a shame to prevent a large portion of the Half-Life players out there from seeing that part of the story.
When this mod is done I will probably fire it up with a friend of mine that never had the chance to play Half-Life on the PS2. It's been a while since I played through Decay (though I certainly played through it quite a bit while we were working on it). -Patrick Deupree (Originally posted on the VERC)
From the Valve Developer Community Wiki
Installation Guide and Singleplayer
Half-Life: Decay was made for Co-op so anyone wanting to play singleplayer must constantly switch between both characters by pressing the “G” Key on their keyboard. The bot controlling the other character is just basic AI and is only capable of defending itself and nothing else, movement must be made by the players themselves.

You must have Half-Life (not Half-Life: Source) installed in your Steam Library and directory.


Download the fan made port of Half-Life: Decay (the file name should be decay_eng.exe)
File: Half-Life: Decay Fan Created Port[decay.half-lifecreations.com]

Double click decay_eng.exe and follow the installation wizard. If asked to Choose where your Half-Life directory is, simply choose “common” from the 'Steam account:' dropbox field in the installer.

'Half-Life' should appear under 'Game folder to install Decay to:'

After this, a new folder called 'decay' should show up on your Steam Directory INSIDE your Half-Life folder.

Run Half-Life and from the main menu, click 'Change game' (if you can't find 'Change game' in your Half-Life menu, see STEP 5) and choose Decay. The game should now be available for Singleplayer.

STEP 5: (OPTIONAL: Follow this if 'Change game' is not in your Half-Life Menu)

Go to: \Steam\steamapps\common\Half-Life\valve\resource\GameMenu.res, open it with notepad and paste the entire code from this guide (not the CS 1.6):
Change Game from Main Menu Guide.[github.com]

STEP 6: How to start a Singleplayer Game
Click 'Play Decay' and select dy_accident1 in the map options. All other maps are locked and can only be unlocked by playing through the game.

It should look like this:
Setting Up Dedicated Server and Online Co-op
Follow STEP 1, 2 and 3 on the Installation Guide and Singleplayer section as seen above. Disregard if you've already done the above steps.

Make a folder called 'dedicated server' anywhere you want.
ex. C:\dedicated server

STEP 3: Setting up a Dedicated Server
Download SteamCMD and then unpack its contents preferably on its own separate folder to keep things clean.

Double click Steamcmd.exe (it should have a Steam Icon). A command prompt will appear and will attempt to update. Just let it do its thing and wait until it finishes updating.

After the update, you should now see the command line “Steam>”
Now type the following commands IN ORDER:
  • login anonymous
  • force_install_dir C:\dedicated server (or wherever you created your dedicated server folder earlier)
  • app_update 90 validate
The first attempt will ALWAYS FAIL! Don't panic and proceed to STEP 6 =)

After it FAILS to download the first time, just type app_update 90 to validate it again. This time, it should finish downloading all the proper files.

COPY (not cut), your 'decay' folder from your Half-Life directory (Steam\SteamApps\common\Half-Life), into your dedicated server folder (c:\dedicated server)
Note: Be sure to copy the entire folder and not just the contents

Inside your 'dedicated server' folder, double click an exe file called 'hlds.exe' (should have a red Half-Life (Lambda) icon). It will open a GUI where you can setup your own server.

Put the following entries:
Game = Decay
Server name = (whatever you want your server to be called)
Map = dy_accident1
Network = Internet
Max. players = 3 (no more no less)
UDP Port = 27015
RCON Password = (whatever you want it to be)
Check “Secure (Valve Anti-Cheat)” -or not, your call

Click 'Start Server' and your server should now be up and running, all we have to do now is set up the map cycle order.

STEP 10:
Under the 'Main' tab, double click Map Cycle and enter the maps in this order:

STEP 11:
Run Half-Life and from the main menu, click 'Change game' (if you can't find 'Change game' in your Half-Life menu, see STEP 5 on the SINGLEPLAYER section above) and choose Decay.

Click 'Find Servers' (you should, if you followed the Steps correctly, find your newly set up Server there)

If you're the host, the server should appear in both your Internet Tab and your LAN tab. For your friends, it will appear only on their Internet Tab (unless you're in the same network, in that case, it will also appear on his/her LAN tab)
Server not showing up on Friend's Internet Tab?
If you've followed the guide to the letter and was able to setup a dedicated server and you yourself see the server but your friends don't, then that means you need to do some Port Forwarding with your router but that's a matter outside my guide's scope.

This should not be a problem when you and your friends are playing in LAN.
Steam Library Icon and Name Fix
A 'new' game with no Icon should have appeared in your Steam Library called 'Decay'.

This is a Shortcut made by Steam for you to quickly access Half-Life: Decay.

If you want to give the shortcut an Icon and rename it to Half-Life: Decay, simply download this file: HL Decay Icon Patch

Unzip it and copy paste the contents to: "Steam\SteamApps\common\Half-Life\decay"

Your half-life/decay folder should look something like this:
Taken with DiamonD Half-Life Final mod Weapon and hand models.

Thanks to Azrak for helping me test this out.
Thanks to soulsynapse and ♥ Sora ♥ for helping me set up my Rounter Ports

Credit to DarkIce for his excellent Complete Lost Packs Guide where I found out about Half-Life: Decay and several other great mods to improve your Half-Life (1) experience.

Credit to 'y0ursource' for his very helpful SteamCMD and Dedicated Server Guide[github.com].

Credit to 'MaxKorz' for his Change Game from Main Menu Guide.[github.com]

Credit to 'kamilo' for his Steam Icon fix

Credit and a big thank you to the guys at Half-Life Creations[decay.half-lifecreations.com]for porting this game to the pc. Again, thank you for all your hard work!
Other Related Contents
Shameless self-promotion
If you're interested, also see my:

1. Curator's Page: Miyumi's Review Corner
2. Half-Life Review
3. Half-Life: Opposing Force Review
4. Half-Life: Blue Shift Review
5. Black Mesa Review
agrastiOs Jun 11 @ 3:05am 
From jack_x in the game's ModDB page:
Is stuff like the text in the options menu being messed up? There is an easy fix:
1) Go to where your Half-Life directory is and from there go to valve/resource. Copy the file that's called gameui_english.txt.
2) Back from the root of your Half-Life directory, this time go to decay/resource and erase the gameui_english.txt file that's already there. Now paste the other gameui_english.txt that you copied before here.
3) While still in the decay/resource directory, open the new gameui_english.txt file if you want to make slight changes that were in the original file. Find the line that defines GameUI_GameMenu_CreateServer and on that same line replace "Create server" with "Play Decay". Similarly, find the line that defines GameUI_CreateServer and on that same line replace "Create Server" with "Choose Mission...".
Brandmaniac λ Jun 9 @ 3:13am 
does couch split screen co-op work
MapleCrepês Jun 8 @ 1:52pm 
(i am paying on the anniversary edition of HL)
to anyone who sees this, there's NO need to paste the entire GameMenu.res code from the link, or it messes up the menu.

simply find the section titled #GameUI_GameMenu_ChangeGame (for me it's 17 in the file), and add two forward slashes (//) in front of "notsteam", "notsingle", and "notmulti" . it should look like this:

"label" "#GameUI_GameMenu_ChangeGame"
"command" "OpenChangeGameDialog"
//"notsteam" "1"
//"notsingle" "1"
//"notmulti" "1"
"HelpText" "#GameUI_MainMenu_Hint_ChangeGame"

then you're done! :)
roccocan Apr 27 @ 5:09am 
nvm i got it
roccocan Apr 27 @ 5:07am 
what checkbox with E
Timmy Majungatholus™ Apr 26 @ 2:08am 
I'm stuck at Step 5
I always get the message "Please use force_install_dir before logon!"
Please Help
Bad at names man Mar 20 @ 4:39am 
no of course it doesnt work for black mesa its on a completely different engine????
Fuzz409 Jan 27 @ 4:43pm 
and it will use steam networking
Fuzz409 Jan 27 @ 4:43pm 
ignore all this, to play with freinds just click "Play Game" and checkmark the box that says "E", then it will appear in the internet tab
SpatialRug Jan 18 @ 2:37am 
Does it work also for black mesa?