BLT4L is a part clean-room, part-line-by-line rewrite of BLT, the PAYDAY 2 Better Lua injecTor, for Linux. It is compatibile with all BLT mods, presents the same API, and uses the same LUA base.

BLT4L is presently not maintained, much of the work and research that was done to get BLT4L working has gone in to SuperBLT which can run all of your BLT mods (and more!).

• Roman Hargrave - Initial work, code, translations from BLT4WIN
• Campbell Suter - BLT2 updates, and maintenance
• Leonard König - C++ cleanup, linker work
• Ozymandias117 - Fixed subhook on 64-bit platforms
• James Wilkinson - BLT LUA (and BLT)

You can install BLT4L in a few different ways. The quickest way is to clone this repository, and run install.sh. This will work best on Debian, or a Debian derivative, such as SteamOS, as it can help you install missing dependecies.

If you're on Arch Linux (or a derivative like Manjaro), you can install the AUR package blt4l. This package uses the new launcher script, works with or without the Steam runtime, and will automatically install the base Lua if it's not present.

You can also find prebuilt copies under the releases tab, or if you want to debug or modify BLT4L, you can build it manually.

• openssl (libssl-dev on some ubuntu systems - 18.04 in particular)
• curl4-openssl (gnutls is NOT supported)
• zlib
• cmake
• a build tool chain (most distros have one preinstalled, or available in a build-essentials package)

• libc++dev
• clang (3.8+)

$ git clone https://github.com/blt4linux/blt4l.git
$ cd blt4l
$ git submodule init
$ git submodule update
$ mkdir build 
$ cd build
$ cmake -DUSE_LIBCXX=1 .. 
$ make

Note: If you opted to not install the extra prerequisites for custom asset-loading, then you can remove the variable -DUSE_LIBCXX=1 from the cmake command.

You should find the hook in your build folder, named libblt_loader.so. You will need to set LD_PRELOAD for the PAYDAY2 process to find the loader.

Next, you will need to copy a LUA mod base to your PAYDAY 2 folder (or whatever working directory you intend to run PAYDAY 2 in). There is a symlink to the BLT LUA mod base (from the BLT4WIN submodule) under lua/mods.

If you set everyting up correctly, you should be up and running with the BLT mod API in PAYDAY 2.

Because our hook writes to executable sections of payday2, SELinux doesn't like us (and it shouldn't). In order to add an SELinux exception for the BLT Hook, you must do the following:

Run Payday2 with libblt_loader.so (It will crash, and SELinux will log the error)

$ sudo ausearch -c 'payday2_release' --raw | audit2allow -M my-payday2-hook
$ sudo semodule -i my-payday-hook.pp

By default, any Lua error (outside of a pcall block) will immediately crash the game, and generate a error.txt file (found in mods/logs) containing the backtrace.

In some situations, it might be useful to continue the game running despite the errors. In that case, set the BLT_CRASH environment variable to CONTINUE. This can be done by prepending BLT_CRASH=CONTINUE to the game launch arguments in Steam.

BLT4L contains some additional Lua functions not present in windows PAYDAY.

The first set of these are in the vm table, and are functions copied from Lua 5.1 that are missing or have different behaviour in PAYDAY:

• vm.dofile
• vm.loadfile
• vm.load
• vm.loadstring (loadstring seems to be present in current versions, however)
• vm.pcall
• vm.xpcall

The Linux version of PAYDAY is also missing a couple of key Lua APIs that are commonly used by mods.

The first thing here is the SystemFS API. Many mods rely on this to save and load files. While BLT4L has added in some of these functions, it is very hard to determine the return types of some functions. Mods should use the Lua io table wherever possible.

Many of the DB functions are missing - in particular, DB:create_entry is missing, which is how mods usually load custom assets (models, textures, etc) into the game. Work is (slowly) being done to reverse-engineer and reimplement this by @RomanHargrave and @ZNixian, however due to the difficulty of this task this will probably take a long time. As a result of this, custom heist/weapon/mask mods will not work (anything that goes into mod_overrides will still work, however).

If you find any other Lua functions that are missing in BLT4L, please open an issue.