libretro/wiki/installer.md

level, order

level	order
setup	100

All installer options

The one-line command finds your setup and its BIOS folder. It downloads only the files that are missing or wrong, and checks each one against its fingerprint before writing it. The options below are for anything else: fewer files (one console, one region, only the cores you have), another folder, an SD card, a check without download, or a run from a script.

Example: --platform retroarch --system sony-playstation --region north-america installs only the PlayStation files, and the North American version where there is one per region.

How the command protects your machine is under What the bootstrap does and Trust boundary. The BIOS folder of each setup is on Get your files.

Options at a glance

Read from the installer's own option list, the one --help prints. The Options table below gives each one in full.

One line

# Linux / macOS / Steam Deck
curl -fsSL https://raw.githubusercontent.com/Abdess/retrobios/main/install.sh | sh

# Windows
irm https://raw.githubusercontent.com/Abdess/retrobios/main/install.ps1 | iex

From a clone, run the installer itself. Nothing beyond the standard library is needed, and Python 3.8 is the floor both bootstraps enforce before handing over:

python install.py

Passing options

The shell bootstrap forwards everything after -s --:

curl -fsSL https://raw.githubusercontent.com/Abdess/retrobios/main/install.sh \
  | sh -s -- --platform retroarch --dest /path/to/sdcard/retroarch/cores/system

--dest is the BIOS folder itself: on a card, retroarch/cores/system for RetroArch on Switch, RetroArch/system on Android.

PowerShell needs another form. iex takes the script text as its own argument, so anything appended to irm ... | iex is read as an argument to iex and rejected with A positional parameter cannot be found. Building a script block from the text and calling it passes the arguments through:

&([scriptblock]::Create((irm https://raw.githubusercontent.com/Abdess/retrobios/main/install.ps1))) `
  --platform retroarch --dest D:\bios

What the installer does

1. Detects the host OS and the platforms installed on it.
2. Fetches install/<platform>.json from the same revision the bootstrap verified the installer against, so the file list and the code reading it always come from one commit.
3. Prints the file count and total size, then a safety notice counting the entries the collection cannot serve, how many of those the platform marks required, and why. At a terminal, it then offers to install everything or to choose systems, cores and regions (see below).
4. Hashes what is already in the destination and reports how many entries are present, verified, or present with the wrong contents.
5. Downloads what is missing or wrong, up to 8 files at a time. At a terminal one line shows the progress, the speed and the time left, while in a log each finished file gets its own line. In an interactive run, a download of 1 GB or more is confirmed first (--yes skips the question).
6. Verifies each download against the declared size, SHA-256 and SHA-1 before it touches the destination, then moves it into place with os.replace so a partial file is never visible. A failed attempt is retried up to three times, after 1, 2 then 4 seconds or the delay a Retry-After header asks. A file of 16 MB or more keeps its partial copy (.<name>.part) when a transfer stops, and the next attempt or the next run requests only the rest. A file already there with other contents is moved aside first, see Files you already had.
7. Copies into standalone emulator directories, only with --standalone-copies.

Some cores read their system data below the frontend's save directory, not below the BIOS folder: Azahar's keys, shared font and NAND files, Citra's sysdata, Dolphin's User tree. The file list marks them root: save, and the run writes them below the save directory, which it names before checking files (5 files read from RetroArch's save directory go to ...). For a RetroArch found by its retroarch.cfg, that is savefile_directory as RetroArch expands it (: for its own folder, ~ for the home), saves/ beside the config when the value is default, empty, or names no folder, and the core's own folder below it when sort_savefiles_enable is on, as it is by default. Without a config, a BIOS folder at its default name (system) puts the save directory beside it (saves, /storage/savefiles on Lakka). --save-dir PATH names the save directory itself. When none of these applies, or when savefiles_in_content_dir or sort_savefiles_by_content_enable keeps saves beside each game, those files are left out and the run says why, like the other entries the list cannot install.

Batocera, KNULLI, Recalbox, RetroBat and RetroDECK write the save directory at each launch, one folder per system (by_system in the file list). Their lists already name each system's folder (gamecube/User/GBA/gba_bios.bin), and the run writes below the saves folder beside the BIOS folder (/userdata/saves, /recalbox/share/saves, ~/retrodeck/saves), never reading a retroarch.cfg that only holds the last launch. EmuDeck's RetroArch config names ~/Emulation/saves/retroarch/saves. RetroPie, ROCKNIX, AmberELEC and EmuELEC keep saves beside each game, and RomM keeps them in the browser: their lists record these files as omitted.

A RetroArch run into an empty folder printed this on 2026-10-21:

Fetching file index for retroarch...
  8069 files (6.5 GB)
  Not installable: 11 files (1 required, not found: 11).

Checking existing files...
  0/8069 present (0 verified, 0 wrong hash)

When the manifest leaves entries out (a file the collection cannot supply, or one that failed its hash check), a Not installable: line under the index count says how many and why. --check and the closing report also name the required ones, grouped by system with the emulators that read them, and point at the emulator pages. They do not change the exit code of --check, since no run of the installer can fetch them.

Reading a run

Each line a first install prints, and what it means. The run below is a Batocera install into an empty folder, from the list as published on 2026-10-21. The figures change with each release.

Before the run

The size depends on the platform and changes with each release. The run prints it before downloading, and asks first when the download reaches 1 GB. The installer also measures the free space and refuses before writing anything if there is not enough.

curl or wget, and Python 3.8 or newer, are checked by the command itself: it stops with a message naming what is absent. PowerShell's execution policy does not block the Windows line. The policy governs script files, and the command never writes one.

The first lines

RetroBIOS 8c0e9c762d2f

Detecting platform...
  Found Batocera at /userdata/bios

The code after RetroBIOS identifies the installer: it is the start of the SHA-256 the command checked before running it. The path is the folder it will write to.

The file index and the download

Two phases follow. The first reads what is already in the folder. It takes a few minutes on a memory card, because every file is hashed:

Fetching file index for batocera...
  14481 files (9.1 GB)
  Not installable: 399 files (79 required, not found: 399).

Checking existing files...
  0/14481 present (0 verified, 0 wrong hash)

Not installable counts the files of the list that the collection does not hold. They are named at the end of the run.

On a first install the present count is zero. On a later run it counts what is already there, and only the rest is downloaded. A download of 1 GB or more is confirmed first (Download 9.1 GB to /userdata/bios? [Y/n]).

The second phase downloads what is missing, one line per file:

Downloading 14481 files (9.1 GB)...
  Press Ctrl+C to stop. Running the same command again carries on from here.
  [1/14481] 3do_arcade_saot.bin ok
  [2/14481] 3dobios.zip ok

Ctrl+C is safe at any point. Files already installed stay, and running the command again picks up where it stopped.

The end of the run

Done. 14481 files installed, 0 files already up to date.
Location: /userdata/bios
399 files were not installed: the collection does not hold them, or its copy fails their check.
  Needed to start an emulator (79 files):
    dark-forces (theforceengine): DARK.GOB, SOUNDS.GOB, SPRITES.GOB, TEXTURES.GOB
    dark-forces-ii (openjkdf2): openjkdf2/episode/JK1.gob, openjkdf2/episode/JK1CTF.gob, openjkdf2/episode/JK1MP.gob, openjkdf2/resource/Res1hi.gob, openjkdf2/resource/Res2.gob
    diablo (devilutionx): devilutionx/diabdat.mpq
    doom3 (dhewm3): base/pak000.pk4, base/pak002.pk4, base/pak003.pk4, base/pak004.pk4
    droidworks (openjkdf2): dwCD.GOB, dwHD.GOB, dwMin.GOB, dwStream.GOB
    fallout (fallout1-ce): fallout1-ce/critter.dat, fallout1-ce/master.dat
    fallout2 (fallout2-ce): fallout2-ce/critter.dat, fallout2-ce/master.dat
    fury (fury): fury.grp
    ... and 9 more systems (--check --verbose lists them all)
  Each emulator's page says what these files are: https://abdess.github.io/retrobios/emulators/
To check this later, run the same command with --check.

The word Done and a location are the confirmation. Any other ending (Stopped, Finished with errors, Nothing was installed) means something was left undone, and the run says which case it was.

The lines between Location: and the --check hint name the files of the list that the collection does not hold. Needed to start an emulator gives, for each system, the emulators that read it and the files they cannot start without. On the run above, all 79 belong to games (Dark Forces, Diablo, Doom 3, Tomb Raider and the others): the engine reads them from a copy of the game itself. The other 320 are optional, and the emulators reading them start without them.

A later check

The same command with --check reads the folder and writes nothing:

Checking existing files...
  14481/14481 present (14481 verified, 0 wrong hash)

  All files up to date.

The files the collection does not hold are listed after it again, as long as they are absent from the folder. A number before wrong hash means a file is present with contents the platform does not accept. Running the install again replaces it and keeps the old one, see Files you already had.

Files you already had

A file in the BIOS folder whose contents differ from the expected one (another revision, a personal dump) is replaced, but never lost. Just before the verified copy takes its place, the old file is moved to a dated folder beside the BIOS folder, under the same path:

~/.config/retroarch/system/scph5501.bin                    the verified copy
~/.config/retroarch/retrobios-backup/20261022-153000/system/scph5501.bin   yours

A file with the expected contents is never copied, and nothing is kept when nothing is replaced. The end of the run says how many files were kept, their size, the folder, and the command that puts them back:

Kept 1 file you had (512.0 KB), which the collection's copies replaced, in /home/me/.config/retroarch/retrobios-backup/20261022-153000
  To put them back: python3 install.py --restore /home/me/.config/retroarch/retrobios-backup/20261022-153000

--restore FOLDER copies every file of that folder back to its place and leaves the folder as it is, to delete once the emulators start as before. Copying the contents of the dated folder into the folder that holds retrobios-backup does the same by hand. --dry-run --restore FOLDER lists what would go back. --dry-run alone counts the files an install would keep.

The folder is beside the BIOS folder, not inside it, because some emulators find a BIOS by its contents and not by its name. DuckStation, SwanStation and Rustation read every file of the BIOS folder, and BizHawk walks its firmware folder with every subfolder: an old copy anywhere inside could be picked instead of the new one. Only when nothing can be written beside the BIOS folder (a drive root, a parent folder that refuses writes) does retrobios-backup go inside it, and the same --restore puts the files back. A file that cannot be moved aside is not replaced: it stays, and the run reports it as failed with file in place could not be kept aside.

A BIOS folder can sit on a network share other people write to. So a retrobios-backup that is a link is never written through (the backup goes inside the BIOS folder instead), and --restore only takes a folder the installer created, marked by a .retrobios-backup file, without following links found inside it.

On one drive the old file is moved, not copied, so keeping it needs no space beyond what it already used. A link sitting at a file's name is not kept: the file it points to is never touched. Data trees and --standalone-copies keep their replaced files the same way, beside the folder they were in.

Choosing what to install

By default the installer fetches everything the platform runs. At a terminal, after detection, it asks:

RetroArch: 8069 files, 6.5 GB.
  Enter) install everything
  i) only what the installed cores read: 100 files, 44.2 MB
  c) choose systems, cores and regions
  q) quit

i appears for RetroArch, Lakka and RetroPie when cores are found installed, and the line above is a RetroArch with Beetle PSX HW, Snes9x, mGBA, Genesis Plus GX and FCEUmm. It keeps what those cores read and drops the systems none of them emulates, the rule --installed-cores applies.

c walks through three numbered lists, each answered with numbers such as 1,4,7-9, or Enter to keep everything on that axis.

• Systems. The consoles and computers the platform declares. A last entry, other, holds what cores load for systems the platform does not list, such as game engines and extra computers. Choosing systems leaves it out unless it is chosen too, as generate_pack.py --system does.
• Cores. The platform's own BIOS list for the chosen systems is always kept. This narrows only the extra files each emulator core loads beyond it. Asked only when the chosen systems have such files.
• Regions. Asked only when a chosen system has one BIOS per region. The numbers give an order of preference: 2,1 keeps the second region where a file for it exists, and the first one elsewhere.

The run then prints the options that repeat the same choice without questions, for instance --platform retroarch --system sony-playstation --region north-america.

The same choices on the command line:

python install.py --platform retroarch --list-systems
python install.py --platform retroarch --system sony-playstation,nintendo-gba
python install.py --platform retroarch --system sony-playstation --core pcsx_rearmed
python install.py --platform recalbox --region us,eu,jp
python install.py --platform emuelec --no-game-data

Firmware without game data

Some platform lists name the files a game reads beside the firmware its emulator needs (the Doom WADs in EmuELEC's list), and the cores' profiles mark the data files of the games they run category: game_data: MAME's software lists, a game engine's own data. The manifest marks each of these files "category": "game_data", and firmware carries no category.

--no-game-data leaves them out of the install, --check and --dry-run, and names what it left out with its category (ten names, --verbose for all):

  Left out as game data (--no-game-data): 2436 files: ports/doom/doom1.wad, ports/doom2/doom2.wad, ...

It is the cut generate_pack.py --no-game-data makes, and a test holds the two to the same file list. A file list that records no category is refused rather than read as having no game data.

Installed cores

--installed-cores reads the cores a RetroArch already has and installs what they need. The cores are the <name>_libretro.so (.dll, .dylib, _libretro_android.so) files in the libretro_directory of the retroarch.cfg detection found, cores/ beside RetroArch when the setting is unset, a retroarch.cfg next to the system directory for a portable install given with --dest, and the folders RetroPie (/opt/retropie/libretrocores) and Lakka (/usr/lib/libretro, /storage/cores) install into. A core file is named the buildbot's way (mednafen_psx), and the manifest maps each name to the profile its files are filed under (beetle_psx).

What stays is what a pack built for exactly those cores carries, the rule --target follows too: a platform system stays when an installed core emulates it or reads its files, or when no core of the platform does. A file a core loads stays when that core is installed. Where two cores read one path and want different bytes, the copy of the first installed core in the builder's order is the one installed. The same holds for a file of the platform's own list: where a core's source contradicts the platform and the frontend only checks the path, the core's copy is installed while that core is, and otherwise the platform's answer, read from the first declaring system that stays.

With --dest and no retroarch.cfg beside the folder, nothing names the cores folder: --cores-dir names it, and the refusal prints the command with it.

Batocera, Recalbox and the other distributions ship their cores with the system, so the option is refused there, as it is when no core is found or when the file list predates the mapping: carrying on would install everything while the option asked for less.

A name the platform does not have is refused before anything is downloaded, since carrying on would install something other than what was asked. The refusal suggests the closest names (playstation gives sony-playstation) and the option that lists them all. Names are matched on letters and digits, so --platform "MiSTer FPGA" and --system "Sony PlayStation" are read as the site writes them. A system name that itself contains commas, as Recalbox's msx1,msx2,msxturbor does, is read as one name. The name a platform gives a system itself is accepted too: on Batocera --system psx is sony-playstation and --system gba is nintendo-gba, the names its roms/ folders carry. They come from the platform's own file, and --list-systems prints them beside each system (nintendo-gba (gba)).

The region rule is the one generate_pack.py --region applies, and a test holds the two to the same file list. In each group of regional alternatives the best-ranked match stays. A file declared for every region beats regional files that match nothing asked. When nothing matches, every regional file stays, so no system is left without its BIOS. A file the emulator does not select by region always stays. The manifest records, for each file, the systems that declare it, and for a regional file, its regions and the groups it competes in. The installer reads nothing else.

The questions are asked only when standard input is a terminal. Piped, scripted or run with --no-input, the installer asks nothing and installs what the options name, everything by default.

Options

Option	Effect
--platform NAME	Install for this platform instead of the detected one. Unknown names are refused with the available list
--dest PATH	Destination directory, overriding detection. Without --platform, the file list is the platform detected here: at a terminal the installer asks, Enter taking the one found, and otherwise it uses the one found, RetroArch's when nothing is found, and refuses when several are. The run prints whose list it is. A folder that does not exist is named with the nearest one that does, then created. When more than its last level is missing (a mistyped path), a run at a terminal asks first, and the answer defaults to no
--target NAME	Keep only the files the cores of that hardware target need, and the systems they emulate. An unknown target is refused rather than ignored, since carrying on would install everything. On Batocera, Recalbox, ROCKNIX and Lakka the board is read from the system (batocera.arch, recalbox.arch, HW_DEVICE, LIBREELEC_DEVICE or LIBREELEC_PROJECT) and applied when no --target is given
--every-board	Install the files of every board instead of the one the system names, for a card that moves between devices
--installed-cores	Keep only what the cores already installed read (RetroArch, Lakka, RetroPie). See Installed cores
--cores-dir PATH	The folder RetroArch loads its cores from, for --installed-cores when it is not found. Implies --installed-cores
--save-dir PATH	The frontend's save directory (RetroArch's savefile_directory), for the files some cores read there, when the run cannot find it. The core's own folder is still added below it when the frontend sorts saves by core
--system NAMES	Install only these systems. Comma-separated or repeated. --list-systems prints the names, other included
--core NAMES	Keep the platform's own list and only the extra files these cores load. --list-cores prints the names
--emulator NAMES	Install what these emulators read on the detected platform, and nothing else: their own files and the platform's files of the systems they run. Each emulator page on the site gives this command. --list-emulators prints the names, buildbot names such as mednafen_psx included
--region LIST	Preferred regions, best first (us,eu,jp): keep one BIOS per region where a system has several. Accepts the names and aliases of generate_pack.py --region
--no-game-data	Leave out game data (a game's own files, not firmware) and install the firmware only. What it leaves out is named. See Firmware without game data
--list-systems	Print a platform's systems with the files and size each holds
--list-cores	Print the cores whose extra files a platform installs
--list-emulators	Print every name --emulator accepts, each buildbot name beside the emulator it stands for
--romm-firmware TEMPLATE	RomM: where each platform's firmware goes in the library, as filesystem.structure.firmware in RomM's config.yml says ({platform}/bios for a library laid out as {platform}/roms). Read from config.yml beside the library when it is there. See RomM firmware layout
--no-input	Never ask a question, even at a terminal
--check	Report and exit without writing
--dry-run	Show what would be downloaded, by system and with sizes, without writing anything
--yes, -y	Do not ask before a download of 1 GB or more
--quiet, -q	Print only failures and the final summary. Implies --no-input
--events	Write the run as JSON events on standard output, one object per line, and the usual text on standard error. Implies --no-input. See Machine-readable events
--restore FOLDER	Put back the files a run replaced and kept in FOLDER, a dated folder inside retrobios-backup. Takes no other option but --dry-run and --no-input. See Files you already had
--version	Print the installer's identity, the first 12 hex digits of the SHA-256 the bootstraps pin
--list-platforms	Print the supported platforms and what was detected here
--list-targets	Print the hardware targets a platform publishes, with the core count each carries
--jobs N, -j N	Parallel downloads, 1 to 32, default 8
--verbose, -v	Print per-attempt failures and hash mismatches
--standalone-copies	Also copy into detected standalone emulator directories
--help, -h	Print the option list, a few examples in the form the run was started with, and the address of this page

--check reads the same file list, hashes the destination and exits, with code 1 when a file is missing or does not match and 0 when every one does. Files with a wrong hash are listed first and in full, then the first ten missing ones (--verbose lists them all). --dry-run counts the data trees in its total. Without it, a file already present with the expected hash is left untouched, and one whose contents do not match is re-downloaded and replaced by the verified copy, the old one kept beside the BIOS folder. Files the list does not name are never read, moved or deleted.

Platform detection

Detection reads what the system itself writes, never a guess from a directory name. A machine runs one embedded system, so every rule below is tested. A system built on another one (KOLOS on JELOS, dArkOS on ArkOS, spruceOS on a TrimUI) matches both and is the one meant. Two unrelated systems matching are both named: at a terminal the run asks which one, otherwise it stops and asks for --dest. The run names the system as it names itself, with the file list it gets: Found AmberELEC at /storage/roms/bios (RetroArch files). --list-platforms lists every system below.

Where a system's RetroArch config is named, its system_directory is the folder, ~ being that system's home for RetroArch. The folder in the last column is used when no config sets one. ArkOS and dArkOS keep two configs (64-bit and 32-bit RetroArch), and their "Switch to SD2 for Roms" script rewrites both to /roms2/bios: a second card is followed through them.

Evidence	System	File list	BIOS directory
/etc/os-release OS_NAME=ROCKNIX (or ID=rocknix on images before 2025)	ROCKNIX	ROCKNIX	/storage/roms/bios
/etc/os-release OS_NAME=knulli or /usr/share/knulli/knulli.version	KNULLI	KNULLI	/userdata/bios
/etc/os-release ID=lakka	Lakka	Lakka	/storage/system
/usr/share/batocera/batocera.version	Batocera	Batocera	/userdata/bios
/recalbox/recalbox.version or /usr/bin/recalbox-settings	Recalbox	Recalbox	/recalbox/share/bios
/opt/muos	muOS	RetroArch	system_directory of /opt/muos/share/info/config/retroarch.cfg, else of the default it is copied from: /run/muos/storage/bios, which muOS binds to MUOS/bios on the second card when that card holds one, else the first. Cores are read from that config's libretro_directory (/opt/muos/share/core)
/mnt/mmc/MUOS/	muOS	RetroArch	/mnt/mmc/MUOS/bios
/etc/os-release NAME=AmberELEC (CHAos writes the same)	AmberELEC	AmberELEC	/storage/roms (its list names bios/, ports/ and neogeo/ there)
/usr/bin/batocera-info naming PAN4ELEC, on AmberELEC	PAN4ELEC	AmberELEC	as AmberELEC
/etc/os-release NAME=EmuELEC	EmuELEC	EmuELEC	as AmberELEC
/etc/os-release OS_NAME=JELOS	JELOS	RetroArch	/storage/.config/retroarch/retroarch.cfg, else /storage/roms/bios
/usr/lib/systemd/system/jelos-ready.service, on JELOS	KOLOS	RetroArch	as JELOS
/etc/os-release OS_NAME=UnofficialOS	UnofficialOS	RetroArch	as JELOS
/etc/os-release OS_NAME=ArchR	ArchR	RetroArch	as JELOS
/home/ark and /opt/system, or title=ArkOS in /usr/share/plymouth/themes/text.plymouth	ArkOS	RetroArch	/home/ark/.config/retroarch/retroarch.cfg then retroarch32/retroarch.cfg, else /roms/bios
title=dArkOS in the same file (the dArkOSRE, dArkOSen and ArkOS4Clone images keep it)	dArkOS	RetroArch	as ArkOS
title=RetroOZ in the same file, /opt/.retrooz or /etc/retrooz_version	RetroOZ	RetroArch	/home/odroid/.config/retroarch/retroarch.cfg then retroarch32/retroarch.cfg, else /roms/bios
/mnt/SDCARD/spruce	spruceOS	RetroArch	/mnt/SDCARD/Saves/ra-configs/retroarch-*.cfg, else /mnt/SDCARD/BIOS
/mnt/SDCARD/System/usr/trimui/crossmix-version.txt	CrossMix-OS	RetroArch	/mnt/SDCARD/RetroArch/retroarch.cfg, else /mnt/SDCARD/BIOS
/mnt/SDCARD/.tmp_update/onionVersion/version.txt	Onion	RetroArch	/mnt/SDCARD/RetroArch/.retroarch/retroarch.cfg, else /mnt/SDCARD/BIOS
/mnt/SDCARD/.allium	Allium	RetroArch	as Onion
/mnt/SDCARD/Koriki/version.txt	Koriki	RetroArch	as Onion
/etc/main and /usr/bin/miyooctl	MiyooCFW	RetroArch	/mnt/.retroarch/retroarch.cfg, else /mnt/.retroarch/system
/mnt/plumos-user	plumOS	RetroArch	/mnt/plumos-user/bios, which its launcher appends to every RetroArch run
/etc/os-release ID=plumos without the folder above	plumOS	none	its builds choose a folder per launch: named, not installed to
/usr/trimui	TrimUI	none	no published source names the stock firmware's folder: named, not installed to
/mnt/SDCARD/.system/res or /mnt/sdcard/.system/res	MinUI	none	MinUI, MyMinUI and NextUI give each core its own Bios/<tag>/, a layout not written yet: named, not installed to
/mnt/vendor/bin/dmenu.bin	Anbernic stock firmware	RetroArch	/mnt/mmc/bios

AmberELEC, EmuELEC and KNULLI install the BIOS list they publish themselves. TheRA is not detected: no image or source of its Odroid Go builds is published, so neither its marker files nor its folder could be read.

Batocera, Recalbox, ROCKNIX and Lakka also name the board they were built for, and that board narrows the install unless --target or --every-board says otherwise (see the options above). A board with no core list of its own is named and gets the files of every board. KNULLI names its board in /usr/share/knulli/knulli.arch but publishes no core list per board, so the run says so and installs the files of every board.

Some platforms keep their BIOS in a fixed directory, and that directory is the evidence. They are looked for after the configurations below, for a platform not already found that way.

Evidence	Platform	BIOS directory
/media/fat/MiSTer	MiSTer FPGA	/media/fat/games
C:\RetroBat\bios or %USERPROFILE%\RetroBat\bios	RetroBat	the same
~/Emulation/bios (Linux and macOS)	EmuDeck	the same
~/.var/app/net.retrodeck.retrodeck	RetroDECK	~/retrodeck
/romm/library/bios	RomM	the same
/romm/config/config.yml	RomM	/romm/library/bios, laid out by its firmware template
~/RetroPie/BIOS	RetroPie	the same
%USERPROFILE%\BizHawk\Firmware	BizHawk	the same
EmuHawk.exe or EmuHawkMono.sh in a BizHawk* folder of the home folder or one level down (~/Games/BizHawk-2.11.1), the newest	BizHawk	Firmware beside it

A --dest given without --platform is first read as an SD card: the MinUI family writes the release name as the first line of .system/version.txt at the card root (MinUI-, NextUI-, MyMinUI-), and that line names the file list.

Desktop installs are read from their own configuration, and several can be found on one machine.

Under WSL both sides are searched. The Windows one is reached through its /mnt/<drive> mount: a C:\ path from a rule or a config becomes /mnt/c/..., and the Windows variables the rules use (USERPROFILE, APPDATA, LOCALAPPDATA, ProgramFiles) are read through cmd.exe when WSL does not pass them. A forced --platform retrobat falls back to /mnt/c/RetroBat/bios.

Evidence	Platform	BIOS directory
HKCU\SOFTWARE\RetroBat LatestKnownInstallPath, which RetroBat.exe writes on every start (read through reg.exe under WSL)	RetroBat	that folder + \bios, before the fixed folders above
~/.config/EmuDeck/settings.sh (Linux and macOS)	EmuDeck	emulationPath + /bios
%APPDATA%\EmuDeck\settings.ps1, else %USERPROFILE%\EmuDeck\settings.ps1	EmuDeck	$emulationPath + \bios, C:\Emulation\bios when it names none (a network install: the $VolName share + \Emulation\bios)
~/.var/app/net.retrodeck.retrodeck/config/retrodeck/retrodeck.json	RetroDECK	paths.rd_home_path, falling back to the pre-migration retrodeck.cfg and its rdhome. A folder RetroDECK moved on its own is followed: files for bios/ go to paths.bios_path, files for roms/ to paths.roms_path, and the run names the new place
~/.var/app/org.libretro.RetroArch/config/retroarch/retroarch.cfg	RetroArch (Flatpak)	system_directory
~/snap/retroarch/current/.config/retroarch/retroarch.cfg	RetroArch (Snap)	system_directory
~/.config/retroarch/retroarch.cfg	RetroArch (native)	system_directory
~/Library/Application Support/RetroArch/config/retroarch.cfg	RetroArch (macOS)	system_directory. At default, ~/Documents/RetroArch/system (portable, Steam build included: Application Support/RetroArch/system)
retroarch.cfg beside retroarch.exe (C:\RetroArch-Win64, C:\RetroArch, Program Files\RetroArch)	RetroArch (Windows)	system_directory. At default or without a config, system beside the exe
%APPDATA%\RetroArch\retroarch.cfg	RetroArch (Windows)	system_directory, read when the exe folder has no config
%ProgramFiles(x86)%\Steam\steamapps\common\RetroArch\retroarch.cfg	RetroArch (Steam)	system_directory
%LOCALAPPDATA%\Packages\1e4cf179-f3c2-404f-b9f3-cb2070a5aad8_*\LocalState	RetroArch (UWP/MSIX package)	system_directory of the retroarch.cfg there, ~ meaning that folder. By default LocalState\system
LaunchBox Data\Emulators.xml	RetroArch (portable)	the system directory that entry points at
LaunchBox Data\Emulators.xml naming EmuHawk.exe	BizHawk (portable)	Firmware beside EmuHawk.exe
$BIZHAWK_DATA_HOME, or $XDG_DATA_HOME/emuhawk-monort-<version> (Nix package)	BizHawk (Unix)	Firmware under it

system_directory is read the way RetroArch expands it: a leading ~ is the home directory, a leading : is the application directory, and default means system next to the application. The LaunchBox installation is located through its Start menu shortcut, the only record of where its installer was pointed.

Android has one frontend with a shared BIOS directory, and the app-private directories of the standalone emulators are unreachable from outside the app under scoped storage.

Evidence	Platform	BIOS directory
<shared storage>/Android/data/<package>/files/retroarch.cfg	RetroArch (Android)	system_directory
/data/data/<package>/files/retroarch.cfg	RetroArch (Android)	system_directory
<shared storage>/Android/data/<package>/files/RetroArch/	RetroArch (Android, Google Play build)	<shared storage>/Android/data/<package>/files/RetroArch/system
<shared storage>/RetroArch/	RetroArch (Android, retroarch.com build)	<shared storage>/RetroArch/system

The packages are com.retroarch.aarch64, com.retroarch and com.retroarch.ra32, the flavours the frontend publishes. The first two are published both on Google Play and on retroarch.com, and the two builds keep their folders in different places (see Android). Both config paths are unreadable from Termux on Android 11 and later, so the directories themselves are what answers on current devices.

ES-DE and LaunchBox are reported when present and nothing is written to them: they reference emulators rather than owning a BIOS directory. ES-DE is looked up at $ESDE_APPDATA_DIR or ~/ES-DE, the two locations its own getAppDataDirectory resolves.

When no platform is found but standalone emulators are (an ES-DE setup with DuckStation and PCSX2, for one), the installer fills their own BIOS folders: the folders of the standalone copies list that exist on the machine, with the files that list names, taken from the EmuDeck file list and then RetroArch's. At a terminal it asks first. --check and --dry-run work as for a platform. With --system, --core, --emulator, --region or --target the run asks for a platform as before, since those name a platform's lists.

When a platform named with --platform is not found on the machine, the destination falls back to the directory its detection looks for: /userdata/bios for Batocera, /recalbox/share/bios for Recalbox, /storage/system for Lakka, ~/retrodeck for RetroDECK, ~/Emulation/bios for EmuDeck (C:\Emulation\bios on Windows), /storage/roms/bios for ROCKNIX, /userdata/bios for KNULLI, /storage/roms for AmberELEC and EmuELEC, /media/fat/games for MiSTer, ~/RetroPie/BIOS for RetroPie, /romm/library/bios for RomM, C:\RetroBat\bios for RetroBat, and RetroArch's own default system directory for RetroArch. BizHawk has no such folder: it reads Firmware beside its executable wherever the archive was extracted, so a forced --platform bizhawk that finds no install stops and asks for --dest. MinUI, NextUI and MyMinUI keep their files on the SD card, which the installer reads from a computer it is mounted on: a forced --platform minui stops and asks for the card's root as --dest, and a --dest that is a folder inside such a card (its Bios/) is refused with the root to name instead. On Android a forced --platform retroarch falls back to <shared storage>/RetroArch/system instead, a home directory there belonging to Termux rather than to the frontend. Pass --dest to say where instead of relying on that.

With nothing detected, the installer lists the platforms and asks. With several detected, it asks which one. Both prompts need a terminal: piped into a script with no platform to install for, it prints the manual invocation, in the form the run was started with (the one-line command for a one-liner user), and exits 1.

Standalone copies

Some files are read by a standalone emulator from its own data directory rather than from the platform's BIOS tree. --standalone-copies copies them there after the install, and only then: without the flag nothing is written outside the selected tree, apart from the files kept in retrobios-backup.

The manifest carries the list, fifteen entries on the six platforms that declare them (Batocera, EmuDeck, Recalbox, RetroArch, RetroBat, RetroDECK):

Files	Copied to
prod.keys, title.keys	yuzu, eden, citron, suyu and Ryujinx key directories
Citra/sysdata/aes_keys.txt, Citra/sysdata/boot9.bin	Azahar sysdata
scph*.bin	DuckStation bios
ps2-*.bin	PCSX2 bios, native and Flatpak
GC/USA/IPL.bin, GC/EUR/IPL.bin, GC/JAP/IPL.bin, dsp_rom.bin, dsp_coef.bin	Dolphin, per region for the IPL
PPSSPP/ppge_atlas.zim	PPSSPP PSP/SYSTEM
dc/dc_boot.bin, dc/dc_nvmem.bin	Flycast data, native and Flatpak

An entry names one file or a glob, and one entry carries no file at all: when an RPCS3 configuration directory is present it prints that PS3UPDAT.PUP is installed through RPCS3's own File menu, since that firmware is an installer to run rather than a file to copy.

Targets are per OS, WSL falling back to the Linux ones. A directory that does not exist is skipped rather than created, so nothing is copied for an emulator that is not installed. A destination that is already a symbolic link is replaced by the file rather than written through: a write through the link would land outside the folder the user opted into. The summary counts each copy as copied, skipped (folder absent) or failed, and names every failure. A run without the flag lists the emulator folders of this list that exist on the machine, and says nothing when there are none.

RomM firmware layout

RomM 5.4 places each platform's firmware where filesystem.structure.firmware in its config.yml says, relative to the library: bios/{platform} by default, the layout of the pack. A library laid out as {platform}/roms makes RomM stop until config.yml declares its templates, and RomM suggests firmware: "{platform}/bios" for it.

The installer reads that value from config.yml in the config folder beside the library, /romm/config/config.yml inside the container, and places each file accordingly: with {platform}/bios, psx/scph5501.bin goes to library/psx/bios/scph5501.bin. --dest still names the library's bios folder, whose parent is the library. Run from the host of a container, where config.yml sits elsewhere, --romm-firmware gives the same value. A library laid out as {platform}/roms with no template found is refused rather than filled in the wrong place, and the message gives the command.

Android

Android reports itself as Linux, so the runtime is named from its own variables instead: ANDROID_ROOT and ANDROID_DATA, which Termux inherits, with /system/build.prop covering a shell started without them.

Detection then looks for each installed RetroArch package. Its retroarch.cfg is read from the app external files directory and then from the internal one, the order the frontend itself follows (RetroArch v1.22.2, UserPreferences.java:36-89), and a system_directory it names is used as written. Left at default, it resolves against <storage>/RetroArch (platform_unix.c:1670-1697), where <storage> depends on the build (MainMenuActivity.java:182-183):

Build	Packages	<storage>
Google Play	com.retroarch, com.retroarch.aarch64	<shared storage>/Android/data/<package>/files
retroarch.com	com.retroarch, com.retroarch.aarch64, com.retroarch.ra32	<shared storage>

The two builds share their package ids (pkg/android/phoenix/build.gradle:46-95), so the build is told by what it wrote. The version code the launcher records in retroarch.cfg (bundle_assets_extract_version_current) is below 1609632000 for a Google Play build and the build time in seconds for the others (build.gradle:42, 168-175). Without a readable config, a RetroArch folder under Android/data/<package>/files is the Google Play build, and <shared storage>/RetroArch is the retroarch.com build, the Google Play build never asking for shared storage (MainMenuActivity.java:199-202). When nothing tells them apart, the run names both folders and asks for --dest. The Google Play folder sits in Android/data, which Termux cannot write on Android 11 and later: the run then names it, as it does for Flycast below.

Two Android emulators keep their BIOS elsewhere. DraStic reads /data/data/com.dsemu.drastic/files/DraStic/system, private to the app, and Flycast reads Android/data/com.flycast.emulator/files/data in shared storage, which Android 11 and later keep from other apps. No app can write the first without root, and Termux cannot write the second on Android 11 and later. When either emulator is installed and its folder is out of reach, the run names it and the files that are not copied. Where the Flycast folder is writable (Android 10 and earlier), it is a standalone copy target.

Under scoped storage the two RetroArch config paths are unreadable from Termux on Android 11 and later, so on current devices the folders are what answers. Running termux-setup-storage once is what makes the shared one reachable:

pkg install python
termux-setup-storage
curl -fsSL https://raw.githubusercontent.com/Abdess/retrobios/main/install.sh | sh

EXTERNAL_STORAGE overrides the storage root for a device that mounts it elsewhere. A custom BIOS directory is still named directly:

python install.py --platform retroarch --dest /storage/emulated/0/RetroArch/system

On a handheld: the RetroBIOS port

On a Linux handheld that runs PortMaster (ArkOS, ROCKNIX, AmberELEC, muOS, KNULLI and the others it supports), the installer also runs from the device itself, as a port with gamepad screens. The screens are PortMaster's own, so the port carries no graphics code.

Getting it. Two ways:

• From PortMaster's catalog, once the port is accepted there: open PortMaster, find RetroBIOS under the Other genre, install.
• RetroBIOS.zip, attached to each release cut since the port was added, copied into PortMaster's autoinstall folder. Starting PortMaster then installs it, with or without a network connection. PortMaster's FAQ names the folder: /roms/ports/PortMaster/autoinstall/ on AmberELEC and ROCKNIX, /roms/tools/PortMaster/autoinstall/ on ArkOS, /mmc/MUOS/PortMaster/autoinstall/ on muOS, /userdata/system/.local/share/PortMaster/autoinstall/ on KNULLI.

From a clone of the repository, python scripts/build_port.py builds the same archive into dist/RetroBIOS.zip.

What it shows. RetroBIOS appears among the ports. Started, it runs install.py --check --events and opens on the result: the system's name, how many BIOS files are present, missing, or present with a hash that does not match. The menu offers to update everything missing, to choose systems (each listed with what it lacks, selected or cleared with A), to check again, or to quit. An update shows a progress bar, one step per file, then what was installed, what failed and why, and what the collection cannot supply. Every list has its own Back or Quit entry, since older PortMaster releases do not read B there.

What it needs.

• A network connection: the list of files to check comes from the internet, as do the files. Without one the port says so and offers to check again.
• Python 3.8 or newer. The port uses the system's python3 when it is recent enough, else PortMaster's python_3.11 runtime on aarch64 devices, which it downloads through PortMaster on first use. An armhf device with an older Python is told so, with the computer route below.
• A BIOS folder the installer detects (see Platform detection). On a system it does not know yet, the port says it found no BIOS folder.

The computer route. With the SD card mounted on a computer, the one-line command fills it, naming the platform and the card's BIOS folder: --platform <platform> --dest <BIOS folder on the card>. The port's screens for an unknown system or an old Python name this route.

Which installer runs. The archive carries install.py, the file the one-line command of the same commit downloads: the build refuses any other (scripts/build_port.py compares it with the SHA-256 install.sh pins). A port that downloaded the installer at each start against a pinned SHA-256 would stop working at the next change to install.py, since the pin is fixed when the port is built. The file lists come from main, as for the one-line command. A newer port version carries a newer installer. When a list is in a format the carried installer does not read, the port says to update it.

The launcher (ports/RetroBIOS/RetroBIOS.sh) and its screens (retrobios/screens.txt) read the installer through Machine-readable events only.

Where the files come from

Each manifest entry names either repo_path, served from the repository at the pinned revision, or release_asset, served from the large-files release for the files above the size GitHub carries in a tree. Everything else in the entry (dest, size, sha1, sha256, cores) describes what must land where and what it must hash to.

Entries the collection cannot satisfy are not silently dropped: they travel in omitted_files with a reason, and the run prints the count before downloading anything. not_found means no file in the collection matches the entry, which is what the gap analysis tracks (Reference: What the packs do not hold).

Some cores read a whole tree of data rather than a few files: Dolphin's Sys/, PPSSPP's assets, blueMSX's machines. These are not files of the collection, so data_directories names each tree's source archive (the libretro buildbot, an upstream release) and the sha1 and size of every file the pack carries. The installer downloads the archive once, maps its members the way the pack was built (strip_components for a ZIP, source_path for a tarball, exclude), and writes a file only when its hash matches the list. A file the source has changed since is left out and counted, and the pack still holds it. --check counts the data files missing, --dry-run names each tree it would fetch, and narrowing with --system, --core or --target keeps only the trees of the systems that stay.

What the bootstrap does

Both wrappers do the same four things before any BIOS file is considered.

They fetch install.py over HTTPS only, from RETROBIOS_INSTALL_URL or the pinned raw URL. A URL with any other scheme is refused outright.

They cap the download at 2 MB and require the SHA-256 to equal the 64 hex characters embedded in the wrapper, RETROBIOS_INSTALL_SHA256 when set. A mismatch aborts with "the downloaded installer does not match its expected fingerprint" and nothing runs. Right after an update of this project the wrapper and install.py can come from caches a few minutes apart, which reads the same way: waiting five minutes settles it. Any change to install.py therefore means recomputing that pin in both wrappers.

They locate a Python 3.8 or newer interpreter (python3 then python on POSIX, py -3 then python3 then python on Windows). Without one, install.sh names the command that installs it on the system it runs on (pkg install python in Termux, which it offers to run since Termux installs without root, xcode-select --install on macOS, apt, dnf, pacman, zypper or apk from /etc/os-release), and install.ps1 at a console offers to run winget install Python.Python.3.12, then reads the new PATH and carries on. install.sh needs curl or wget (GNU or BusyBox) and sha256sum or shasum. Windows PowerShell 5.1 still negotiates SSL 3.0 and TLS 1.0 by default and GitHub refuses both, so install.ps1 raises the floor to TLS 1.2 before downloading, and install.sh pins the same floor with curl --tlsv1.2.

They delete the temporary installer on the way out, including on interrupt. Run from a clone, install.sh and install.ps1 reuse the install.py sitting next to them and skip the download entirely. Piped from stdin, install.sh never treats the working directory as a trusted location for it.

Piped from curl, the shell's standard input is the script itself, so install.sh hands the installer the terminal (/dev/tty) when there is one. That keeps the installer's questions working when the script is piped from curl.

Trust boundary

The manifest is fetched over the network and treated as untrusted input. Every path it carries goes through one validator that refuses an absolute path, a drive letter, a backslash, a null byte, a doubled separator, a trailing slash and any .. component, so a destination cannot climb out of the BIOS directory. Manifest, target list and payloads each have a size cap, the file list a count cap, and the sum of the declared sizes is checked against the total the manifest claims.

Symbolic links met under the BIOS root are followed on purpose: they are the user's own layout, and EmuDeck links bios/shadps4/sys_modules into shadPS4's data directory where the emulator actually reads it. The boundary is lexical, not a resolved-path comparison, which is what keeps that case working. Standalone copies are stricter, since they write outside the tree the user selected: a symlink already sitting at the destination is replaced by the file rather than followed.

Changing the installer

install.py runs on the user's machine, often an older handheld, so it stays on Python 3.8 and the standard library alone. The RetroPie 4.8 images (retropie-buster-4.8-*.img.gz) are Debian Buster, whose python3 is 3.7.3: there the bootstrap stops before running anything, and the RetroPie pack from the releases page is the way to install (first install). Tests refuse any 3.9 syntax or API, and one runs the installer end to end under a real 3.8 interpreter, which CI installs beside 3.12 so the check cannot skip. The build scripts need 3.9 and are not bound by this.

Every change to install.py recomputes the SHA-256 pinned in install.sh and install.ps1 in the same commit. The tests compare the pins with the file.

Narrowing by system, core, region or target replays the pack builder's rules from fields the manifest carries, and a parity test compares an installer selection with the pack built the same way. Given a manifest without those fields, the installer refuses to narrow rather than install everything.

Exit status

Code	Meaning
0	everything asked for is installed or already up to date
1	a failure: the one-liner could not download or verify install.py, or found no Python 3.8 (nothing was run), an unusable base URL, an unknown platform or target, --installed-cores with no core found, a manifest that fails validation, a fetch that never succeeded, no platform to install for in a non-interactive run, some files failed while others installed, --check found files to fetch, or --restore could not put a file back
2	nothing was installed: every file the run tried failed (a BIOS folder that cannot be written, for one), the drive has too little free space for the download (checked before any folder is created), or the question about a --dest folder that does not exist was answered no. Also an option the installer refused before any download: an unknown option, --jobs outside 1 to 32, --target with --every-board. The message then starts with install.py: error:. With --restore, a folder that is not a dated folder inside retrobios-backup
130	stopped with Ctrl+C, or with Ctrl+C or Ctrl+D at a question. Run the same command again to carry on
141	the output was piped to a reader that closed early (--list-platforms | head)

install.ps1 passes the installer's code on unchanged: run as a file it exits with it, run through irm \| iex it sets $LASTEXITCODE (an exit there would close the PowerShell window). It declares no parameter of its own, so every argument reaches install.py as typed, short forms such as -v included. Its body runs in a script block of its own, so irm \| iex leaves neither its variables nor its $ErrorActionPreference in the session.

Failures that are per-file, such as a download exhausting its three attempts, are counted and reported at the end.

Machine-readable events

With --events, standard output carries only JSON objects, one per line, and the text a person reads goes to standard error. A program driving the installer (the handheld port is one) reads the objects and never parses the text. Every object has an event key naming its kind, and each kind has exactly the keys below, in this order. The schema is EVENT_KEYS in install.py, and a test holds this table to it.

Kind	Keys	When
start	schema, installer, mode	First line. schema is 1, installer the identity --version prints, mode one of install, check, dry-run, list
detect	os, os_name, platforms	Once the platforms are known. os_name comes from /etc/os-release. platforms lists {platform, name, bios_dir}, and is empty when nothing supported was found
error	stage, reason, platform, message	The file list could not be read (stage is manifest). reason is network, not_found or invalid
file	platform, dest, systems, size, state	Each file of the list after the check. state is present (hash verified), wrong_hash or missing
system	platform, system, name, files, present, missing, wrong_hash, bytes_needed	Each system, sorted by id. Files with no system count under other. name is the platform's own name for it
check	platform, name, bios_dir, files, present, missing, wrong_hash, bytes_needed, data_missing, not_installable	The platform's totals. data_missing counts data-tree files to fetch, not_installable the files the collection cannot supply
download	platform, files, bytes	Before the downloads start
progress	files_done, files_total, bytes_done, bytes_total	At most every half second while bytes arrive
downloaded	dest, ok, reason, size, files_done, files_total, bytes_done, bytes_total	Each finished file. reason says why one failed, and is empty otherwise
summary	mode, installed, up_to_date, pending, failed, skipped, left_out, kept, interrupted	The outcome. pending counts what a next run would still fetch, failed lists {dest, reason}, skipped lists {reason, label, files, required} for the files the collection cannot supply, left_out lists {category, label, files, dests} for what --no-game-data left out, and is empty without it. kept lists {folder, files, bytes}, one per backup folder, for the files in place the run moved aside before replacing them (with --dry-run, would move), and is empty when none. Not written for a listing
end	code	Last line, with the exit status the process returns (see Exit status)

An option refused before the run starts (install.py: error:, code 2) writes no event at all. A program reads a missing end as that case.

Environment overrides

Variable	Effect
RETROBIOS_REF	Branch or tag the file list and the files committed to the repository are read from. Defaults to main. Files the manifest marks release_asset always come from the large-files release, whatever the ref, and that release replaces an asset in place when it is rebuilt. Each release deletes the previous release tags, so a tag holds a file list until the next release. For contributors: release process
RETROBIOS_BASE_URL	Base URL for the manifest and the files it declares. HTTPS only, plain HTTP allowed to loopback for end-to-end tests. Whoever controls this base controls the expected hashes, hence the check. A file list that cannot be fetched names the address, and this variable when it is set
RETROBIOS_OS	Names the host outright (linux, wsl, windows, darwin, android) instead of detecting it
EXTERNAL_STORAGE	Android only, the shared storage root RetroArch builds its default directories from. Defaults to /storage/emulated/0
RETROBIOS_INSTALL_URL	Where the bootstrap fetches install.py. HTTPS only
RETROBIOS_INSTALL_SHA256	The SHA-256 the bootstrap requires of that installer, 64 hex characters. When either of these two is set and the fingerprint does not match, the error names the variable instead of suggesting a retry
RETROBIOS_BOOTSTRAP	Set by install.sh (sh) and install.ps1 (ps1) for the temporary installer they run, so that its hints give back the one-line command rather than python3 install.py
NO_COLOR	Plain text, no colour, even at a terminal. TERM=dumb also turns the live progress line off
HTTPS_PROXY, NO_PROXY	Honoured for every download through the standard library's default proxy handling: one names the proxy, the other the hosts to reach directly

When something goes wrong

The common cases, with the short answer, are on When a game does not start. The details follow.

Network

The installer fetches its manifest, then downloads only the repository or large-files release objects it needs. When a download fails, check that https://github.com opens. Behind a proxy, set HTTPS_PROXY in the environment. A file that fails three attempts is counted and reported at the end, and the next run fetches only what is still missing.

Permission denied

The installer needs to write to the BIOS folder. On Linux and macOS, check who owns it (ls -la). On Batocera, Recalbox and ROCKNIX the folder belongs to root, so the same command with sudo in front of it succeeds. On Windows, run PowerShell as Administrator only for a protected folder.

A file system mounted read-only refuses root too, so the installer does not suggest sudo for it. Linux remounts a card or drive read-only after an error, an unclean removal for one: check it (fsck, or chkdsk on Windows) and mount it read-write again.

A file already in the BIOS folder with the read-only attribute is replaced like any other: on Windows the installer clears the attribute first. file in place is read-only appears only when Windows refuses that too, which a file owned by another account can cause.

Platform not detected

The installer finds a platform from the config files it knows. When it finds none, name the platform and its BIOS folder:

curl -fsSL https://raw.githubusercontent.com/Abdess/retrobios/main/install.sh | sh -s -- --platform retroarch --dest ~/.config/retroarch/system
curl -fsSL https://raw.githubusercontent.com/Abdess/retrobios/main/install.sh | sh -s -- --platform batocera --dest /userdata/bios

&([scriptblock]::Create((irm https://raw.githubusercontent.com/Abdess/retrobios/main/install.ps1))) `
  --platform retroarch --dest C:\RetroArch-Win64\system

--list-platforms lists the platforms the installer knows and the ones it finds here. --help lists the options with examples.

No file list

The installer reads its manifests from the revision the bootstrap checked it against. A platform name is checked before anything is downloaded, so a "No file list" message comes from the revision: RETROBIOS_REF naming a tag that does not exist, or one older than the platform. Unset it, or pick a tag from the releases page (Environment overrides).

Upper and lower case

Linux file systems tell Bios.ROM and bios.rom apart. Windows and macOS do not, by default.

The RetroArch pack is built for every system RetroArch runs on, so it holds one name per file: BIOS.col, never bios.col beside it, since unzipping both on Windows or macOS would overwrite one with the other. On Linux, Mesen-CE opens bios.col and NP2kai opens the lowercase np2kai/2608_*.wav, which the pack only holds as BIOS.col and 2608_*.WAV. The installer checks whether the BIOS folder keeps case and, when it does, also fetches these names. On Linux, use the installer rather than unzipping the pack by hand.

The reverse happens on Batocera and Recalbox, whose lists hold both spellings because their systems keep case: NP2kai reads np2kai/bios.rom and np2kai/BIOS.ROM as two files. Written to a folder that folds case (the share opened from Windows, an exFAT card), one overwrites the other. The installer checks the folder first, keeps one file per name there and lists the ones it left out.

Packs and their parts

scripts/download.py --list and scripts/download.sh --list print the packs of a release. A pack's name lists every platform it serves. Releases up to v2026.10.10 ship RetroArch and Lakka as one RetroArch_Lakka pack, and the next ones give Lakka its own, since Lakka runs on Linux where two names that differ by case are two files. The installer and the download scripts find the right pack either way.

Parts named Pack.part1of2.zip are ordinary ZIPs: unzip each one into the same folder, and check that all of them were downloaded. The name says how many there are. scripts/download.sh and scripts/download.py download every part and check it against the release's checksums before unzipping. Both stage inside the destination folder, never in /tmp, which is a RAM disk on most of these systems.