libretro/wiki/installer.md

level, order, terms

level	order	terms
setup	100	manifest, events, exit code, schema, packager, pin, reproducible

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

Each links to its row in the Options table.

One line

# Linux / macOS / Steam Deck
curl -fsSL https://abdess.github.io/retrobios/i | sh

# Windows
irm https://abdess.github.io/retrobios/i.ps1 | iex

Always type the https://: without it the first request goes out in clear text, and anyone on the way could answer with another script.

i and i.ps1 are install.sh and install.ps1 as of the commit the site was built from, set to download install.py from that same commit. The fingerprint they check and the installer they fetch never come from two different versions. If the site is down, the repository serves the same bootstraps:

curl -fsSL https://raw.githubusercontent.com/Abdess/retrobios/main/install.sh | sh

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

For packagers

A package that must not change under its users takes the installer and its file list from one commit. install.sh of that commit pins the SHA-256 of its install.py, and RETROBIOS_REF makes the installer download every file from the same commit:

commit=<commit>
base=https://raw.githubusercontent.com/Abdess/retrobios/$commit
curl -fsSLO "$base/install.py" -O "$base/install/retroarch.json"
pin=$(curl -fsSL "$base/install.sh" | sed -n 's/^DEFAULT_INSTALL_SHA256="\(.*\)"$/\1/p')
echo "$pin  install.py" | sha256sum --check
RETROBIOS_REF=$commit python3 install.py --manifest retroarch.json

What RETROBIOS_REF does not pin is listed under Environment overrides.

Passing options

The shell bootstrap forwards everything after -s --:

curl -fsSL https://abdess.github.io/retrobios/i \
  | 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. The root of a handheld's card works too when the installer knows that card (muOS, Onion, spruceOS, KNULLI, ROCKNIX and the MinUI family, see Platform detection): the files go where its system reads.

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://abdess.github.io/retrobios/i.ps1))) `
  --platform retroarch --dest D:\bios

Without a network (offline install)

A pack downloaded once installs again with no network, on this machine or on one that has none:

python install.py --from-pack ~/Downloads/RetroArch_v1.22.2_BIOS_Pack.zip
python install.py --from-pack ~/Downloads/RetroArch_v1.22.2_BIOS_Pack.part1of3.zip
python install.py --from-pack ~/Downloads --dest /media/card/retroarch/system

One part is enough to name a split pack: the others are taken from the same folder, and a part that is not there is named before anything is written. The platform is read from the pack's name when --platform is not given. The file list is the one the pack carries (manifest.json), with each file's SHA-1 and size, and every file is checked against it before it takes its place. A data tree (Dolphin's Sys/, PPSSPP's assets) comes from the pack too, not from its source archive. --target reads a core list from the network and is refused with --from-pack. A board found on the device is not applied either: every board's files are installed. At a terminal the run finds a card mounted here, asks the folder when nothing is found, and names the BIOS folder on its menu before anything is copied.

--manifest FILE reads the file list from a copy of install/<platform>.json instead of downloading it. Alone, the files still come from the repository. With --from-pack, the run reads that list and takes every file from the pack: --system, --core, --region and --no-game-data then apply as they do online, and a file of the list the pack does not hold fails as not in the pack. The list's platform has to be the one installed for.

--offline forbids every request, for a device with no Wi-Fi: --check still names the platform and its folder where it finds them, then stops at the file list unless --manifest or --from-pack gives it, and counts the files that need the internet instead of offering to fetch them. A file list or a pack names its platform, not where that platform is: when it is found nowhere here, every run without questions stops before reading it, --check, --dry-run and --no-input included, and names the --dest to give. The run installs the copies found on this machine and downloads nothing. The files left out are missing, not failed: it ends Finished with files missing (code 1), or Nothing installed (code 2) when nothing was installed, at a terminal, without questions and on the full screen alike. The summary event counts them in pending, never in failed. The advice that follows names a pack or a run without --offline, and no --from folder already read. A command it suggests keeps --offline when RETROBIOS_INSTALL_OFFLINE set it, sudo not passing that on. The --plain menu then offers f) copy from a folder or an old card, and its Enter checks the BIOS folder when nothing can be copied.

The full-screen interface

Run at a terminal, the installer opens a full screen that a keyboard or a controller drives. Three presses of A or Enter install everything your setup reads: the setup found here, the plan, then the result. The plan screen says how many files are missing, how much they weigh, how many are in place and how much space is free, before anything is written.

The other choices sit one press away. Choose systems ticks the consoles you play, with the total to download under the list. A long list opens on None: A or Enter there unticks every system, and A on a system then takes that one alone. A on a system (Continue) always opens the confirm screen, which counts the choice before Install: it never installs by itself. Back with nothing ticked keeps the ticks the list opened with. Options sets the preferred regions, game data, the installed cores only, the cores, the parallel downloads, the folder and, for a list with files read from the frontend's save directory, that directory. Each row names the option it sets, and Show the command line gives the same choice as one command for a script. Preview the file list shows what would be downloaded and writes nothing. Copy the BIOS files from your old card or a folder opens the folder browser on the first mounted card, and adds --from: the plan then says how many files that folder holds and how many are left to download, or that it holds none of them. After an install on a muOS, KNULLI or ROCKNIX card, the result offers Put RetroBIOS on this card (update from the console later), and Options has the same row (On a handheld). Files the BIOS folder holds in the wrong place are counted on the plan, and Show the files in the wrong place lists each one with its reason. Back on the plan after a change of options, the folder is checked again, so its numbers are the exact ones for the new choice. Ticked systems get their exact count before the install starts.

Action	Keyboard	Controller (gptokeyb, evmapy)
Move	Up and Down, k and j	D-pad Up and Down
Page	PgUp and PgDn	L1 and R1, D-pad Right and Left inside muxterm
First, last	Home and End, g and G
Continue, open, choose	Enter, and Space outside a list of ticks	A, Start
Tick, untick	Space, Right, Left	X, D-pad Right and Left (X alone inside muxterm, Y with muxterm's own keys)
Back	Esc, Backspace	B, Select (B alone with muxterm's own keys, where Select shows its keyboard)
Options	o, Tab	Y
Filter a long list	/ then type, Enter on a lone match chooses it	muxterm: Select shows a keyboard. Elsewhere none (the setup list puts the SD cards after RetroArch)
Keys of the screen	?, F1 (F1 alone while typing a filter, where the help lists the keys that do not type)
Stop an install	Esc, q, Ctrl+C	B, Select+Start (B alone with muxterm's own keys)
Quit	q, Ctrl+C	B on the first screen
Pause, back with fg (Linux, macOS)	Ctrl+Z

The buttons of each handheld route, muxterm's and a Miyoo's among them, are in the key table of each route.

The bottom line of each screen names what A does on the row under the cursor, in the names of what is held. On a computer it names the keys (Enter Install, Esc Back). Started by a handheld launcher, it names the buttons of that launcher (A Install, B Back, see RETROBIOS_PAD below), and ? shows both the buttons and the keys. Where neither is known, in SteamOS game mode or on a console no launcher named, it gives both spellings (A/Enter, B/Esc), and a narrow screen shortens them to A, B and X. On the regions screen, Left and Right move the region under the cursor up and down the order of preference. During the download, a stop waits for the files in progress, and a second one stops at once. Select+Start on a handheld ends the installer with a signal (SIGTERM), which stops it the same way. Either way the result says how many files were installed, and it stays printed in the terminal once the screen closes, with the command that repeats the run. A run that failed keeps its log and names it, and every other run leaves nothing behind. A path on the result is never split inside a word: one longer than the window takes a line of its own, which the terminal folds. A command breaks only between its arguments, an option kept with its value, each line but the last ending with the continuation its shell reads (a backslash in sh, a backtick in PowerShell), so the lines copied run as one command. Where an option and its path do not fit on one line, the path keeps its last folders after .../, the line under it says it was shortened, and the terminal shows it whole after the screen closes. On Android and on a handheld route the result does not mention Shift, which neither has. Every path a run names is spelled the way its BIOS folder was named, the backup folder and the save directory included (/sdcard/RetroArch on Android, not the /storage/emulated/0 it links to).

It opens only for an install, at a terminal of at least 40 columns and 12 rows (a smaller window says so, with its size, before the first question: The window is 39x12: questions come line by line (40x12 for the full screen).) whose TERM is set, is not dumb and can draw it: where the terminal's description (terminfo) has no way to move the cursor, or moves it with other sequences than the ANSI ones the screen writes (TERM=vt52), the questions come line by line instead, by themselves. A terminal whose description is not found on the machine gets the screen. A listing, --check, --dry-run, --events, --quiet, --no-input, --yes and --restore keep the plain output. Options given on the command line fill the screens in advance and are kept as they are. --system is said on the plan (For 1 of 12 systems (--system)), and Choose systems reads every system again with those ticked. The --plain menu shows it the same way, Enter keeping what --system named and c choosing anew.

Colour is added to words, never put in their place. RetroBIOS in the title, the row in focus and the key the bottom line names first are magenta, files installed or in place green, files missing or left out yellow, failures and a refused folder red, and secondary text dim. Only the 16 basic colours are used, the ones a handheld's console has. NO_COLOR set to any value but an empty one turns colour off, as do TERM=dumb or no TERM, a terminal whose description names fewer than 8 colours and an output that is not a terminal. The text stays the same. The line-by-line questions paint the end of a run the same way.

However the screen ends (Enter on the result, q, Ctrl+C, Ctrl+D, SIGTERM, a hangup), the terminal is given back as the screen found it: the cursor shown, the main screen back, echo and line editing on. Ctrl+Z, or SIGTSTP from outside, gives it back the same way and stops the run, and fg redraws the screen where it was. Ctrl+Z stops it only when a shell with job control started it, the one thing that can resume it: started from a terminal app's -e, a desktop entry or a launcher's sh -c, the key is ignored and the bar says why.

A mouse or a touch screen works too, beside the keys and buttons, in a terminal that reports clicks: those of Linux, macOS, WSL and Termux. A click or a tap on a box (a system, a core, a region) ticks or unticks it, as Space does. On any other row it moves the cursor there, and a second one on that row does what Enter does: one row of a terminal is far smaller than a finger, and the row a screen opens on (Install on Confirm) is never chosen by one tap. The entries of the bottom line press their key, Exit on the result too. One that writes files with no screen after it to look first, Install on the plan and Put it on the card, takes two taps: the first adds click or tap again to it in the accent colour, the second presses it. Install on Confirm, which is that look, Quit, Continue and Close take one, so installing or quitting never takes more than two. A row of Preferred regions stays where it is when it is ticked, its number giving the order, which the list shows sorted the next time it opens. The line that says which rows are in view shows the next page, and the wheel scrolls a list or a text without moving the cursor unless it would leave the screen. Nothing happens until the button or the finger comes up, and only where it went down, on the screen drawn when it went down. A new screen takes no press for its first 400 ms: a double click is two presses at most 400 ms (GNOME) to 500 ms (Windows, macOS) apart and the new screen is drawn on the first release, so the second tap of a double tap that changes the screen does nothing on the new one, and a tap made later acts. The right and middle buttons do nothing. The help and the bottom line of a list of boxes say how a tap acts.

Clicks are off in the Windows console the PowerShell command runs in, which reports no click as a key, with TERM unset or set to dumb, unknown, linux or a name starting with vt, cons or ansi, on a handheld route (RETROBIOS_PAD), and with RETROBIOS_NO_MOUSE set. The installer gives them back on every way out, a stop with Ctrl+Z included. On the command line screen, any screen showing a command and the screen where a path is typed, the terminal keeps the mouse, so text is selected, copied and pasted as usual. The result takes taps, so a touch screen can leave it: it is printed again in the terminal once the screen closes, its commands with it, and its last line says so. Elsewhere, and on the result, hold Shift while selecting. --plain never asks for clicks. Clicks and taps were checked on 2026-10-27 in xterm, tmux, GNU screen 4.09, Windows Terminal (WSL) and Termux on Android 17. macOS Terminal and iTerm2 are not checked yet, nor the key they use to select over the installer.

• --tui asks for the full screen, and names the reason when it cannot open (code 2).
• --plain, RETROBIOS_PLAIN=1 or ACCESSIBLE=1 keep the questions line by line. This is the mode for a screen reader, which reads a full screen badly.

Behind the screens, the installer runs itself with --check --events, then --events --yes and the options chosen: the same events a program driving the installer reads. The file list is downloaded once and handed to each run.

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, the full-screen interface then offers to install everything or to choose systems, cores and regions, and --plain asks the same as questions (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. Copies from this machine what it already holds: a file misplaced in the BIOS folder, and what a folder named with --from has. See Copy from an old card.
6. Downloads what is still 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).
7. 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.
8. Copies into standalone emulator directories, only with --standalone-copies.

The file list names the version of the platform it was built for (Batocera 43.1, RetroBat 8.3.1). Where the system writes its own version in a file, the installer reads it, and when the two differ it says so before the install and again with the result: "This list was built for Batocera 43.1, this machine runs 41. Batocera's own BIOS check may report some files as wrong though they work." The install goes on. The files read are /usr/share/batocera/batocera.version on Batocera, /recalbox/recalbox.version on Recalbox (a release, not a branch build), system\version.info beside the bios folder of RetroBat, and VERSION_ID in /etc/os-release on Lakka and EmuELEC. Nothing is run to find it, and an unknown version says nothing: RetroArch writes its version in no file, KNULLI writes a codename, ROCKNIX the date of the build, and AmberELEC's prerelease tags are not matched to the version its image writes.

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 (with --dest too, when the folder is the config's system_directory, as in the full screen), 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. The full screen says so on its plan and its result.

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 dry run into an empty folder printed this on 2026-10-27:

Fetching file index for retroarch...
  106 files read from RetroArch's save directory go to a folder per core under /home/me/.config/retroarch/saves
  10994 files (6.6 GB)
    3269 BIOS files (4.1 GB), 5089 game data files (2.5 GB) and 2636 data files (38.5 MB).
  Not installable: 37 files (1 required, not found: 37).

Checking existing files...
  0 in place, 10994 missing, 0 wrong copies

The second line divides the first, and every later count of the run (the menu, the plan, --dry-run, the result) is taken from the same list.

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

Looking for setups here...
  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 in place, 14481 missing, 0 wrong copies

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 nothing is in place. On a later run the line 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.
BIOS folder: /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.

When most of a download of 100 MB or more comes from one system, or from one core of a single system, the end of the run says so and what narrowing would save, once that saving is over half:

  mame pulls 336.5 MB of this 349.0 MB download for 3do. --core opera keeps 12.5 MB of it and saves 336.5 MB (96%).

--dry-run prints the same line under its plan.

When some files came from this machine rather than the network, a line under Done says where each came from (38 files copied from E:\, 3 copied from the wrong place in the BIOS folder, 4 downloaded.). See Copy from an old card.

The word Done and the BIOS folder 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 BIOS folder: 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 in place, 0 missing, 0 wrong copies

  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 copies means a file is in place with contents the platform does not accept. Running the install again replaces it and keeps the old one, see Files you already had.

Why a file is refused

Each file --check flags comes with the reason it found and the place each core opens it:

  3 files to download:
    wrong hash: scph5501.bin
      another region: the contents of scph5500.bin (japan)
      opened at /home/me/.config/retroarch/system/scph5501.bin by beetle_psx, pcsx_rearmed
    missing: gba_bios.bin
      nested folder: it is at system/system/gba_bios.bin, a system folder inside system
      opened at /home/me/.config/retroarch/system/gba_bios.bin by mgba
    missing: pcsx/extra.bin
      still zipped: it is inside PSX BIOS.zip
      opened at /home/me/.config/retroarch/system/pcsx/extra.bin by pcsx_rearmed

Reason	What the folder holds
nested folder	The file inside a folder named like the BIOS folder itself (bios/bios/, system/system/)
one folder too deep, 2 folders too deep	The file below its place, as a ZIP extracted into a folder of its own leaves it
one folder too high	The file in the folder above the BIOS folder
wrong folder	The file under its name in another folder
case of the name	A name that differs only by capital letters, on a system where that makes two names (the folder holds SCPH1001.BIN, the cores open scph1001.bin)
still zipped	The file inside a ZIP in the folder, a .7z or .rar of the same name, or a ZIP saved under the file's own name
wrong size	A file of another size than any copy the list accepts
another region, another revision, another file	The contents of another file of the list: another region's BIOS, the copy another core reads, or the one the platform's own list declares
a name no core opens	The right contents under a name no core of the platform reads
same size, other contents	Another dump, or a damaged copy
only a Mac's ._ file	Only the ._name file a Mac writes beside each file it copies to a FAT or exFAT card: Finder data, not the file

The reasons are read from the folder and the file list, nothing else. When three files or more sit too deep in the same folder, a line before the list names that folder once. A file whose exact contents are somewhere in the BIOS folder (too deep, in capitals, still in its ZIP, one folder too high) is put in place by the next install: --check says so under the file, with a run without --check copies it into place. Files with a reason are always listed. The plain missing ones stop at ten unless --verbose is given.

A pack published in parts leaves a marker beside the files of each part (RetroArch_v1.22.2_BIOS_Pack.part1of3.txt). --check reads them and names a part that was not extracted, or one extracted into a folder of its own:

  RetroArch_v1.22.2_BIOS_Pack.zip comes in 3 parts, all needed.
    missing: part 2, RetroArch_v1.22.2_BIOS_Pack.part2of3.zip (1.9 GB)
    Download it and extract into /home/me/.config/retroarch/system, beside the other parts.

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.

Copy from an old card

The card a handheld came with, a backup of an old BIOS folder, a Downloads folder: --from FOLDER copies the BIOS files it holds instead of downloading them.

python install.py --platform muos --dest /media/me/SD1 --from /media/me/STOCK
python install.py --from ~/Downloads --from /media/me/backup
python install.py --check --from /media/me/STOCK

The first line names the root of the muOS card, the one holding MUOS: the files go to MUOS/bios on it, where muOS reads them, and the run says so.

Every file is recognised by its contents, never by its name: PSX BIOS (USA).bin in a subfolder lands as scph5501.bin when it holds those bytes, and a file of the right name with other bytes (an empty file left by a CFW, another revision) is not taken. The folder is searched with every subfolder, and inside each ZIP it holds, for a file the list wants loose and for an archive it wants whole (neogeo.zip). Only files whose size is one the list expects are hashed, so a large card is read quickly. The ._ files a Mac writes, the system folders (System Volume Information, .Spotlight-V100, .Trashes, $RECYCLE.BIN) and a link leading out of the folder are skipped. --from also takes a ZIP of an old BIOS folder.

The search stays on one drive: a drive mounted inside the folder is named and not entered (give it its own --from), and so are /proc, /sys, /dev and Windows junctions. The root of the system (/, C:\) is refused. A file that cannot be read, and has the size of a file still missing, is named with the reason (E:\bios\a.bin could not be read: Permission denied), as is a ZIP member locked by a password.

The folder is only read: each file is copied, checked against the list's hashes once written, and the original stays where it is. A file in place with other contents is kept aside first, as a download would replace it (see Files you already had). What no folder holds is downloaded as usual, or taken from the pack with --from-pack. Several --from are read in the order given, and the end of the run says where each file came from:

Done. 44 files installed.
  38 files copied from E:\, 4 downloaded, 2 still missing.

--check --from FOLDER writes nothing and says how many files the folder would give (E:\ holds 38 of these files: a run without --check copies them.), with each file's place in it. --dry-run counts them apart from the download.

The BIOS folder itself is read the same way. A file the list wants that sits misplaced in it, in a bios/bios/ folder, a pack extracted into a folder of its own, a name in capitals on a system where case counts, a ZIP never extracted, or one folder above, is copied where the cores open it, with no --from needed. The misplaced copy is left as it is, and the end of the run counts them (3 copied from the wrong place in the BIOS folder).

Choosing what to install

By default the installer fetches everything the platform runs. At a terminal, the plan screen of the full-screen interface offers Install, Choose systems and Options. With --plain, or where the full screen cannot open (a terminal smaller than 40x12, TERM=dumb), the same choice comes as questions after detection. A RetroArch run with --plain printed this on 2026-10-28, g then pressed:

RetroArch: 10994 files, 6.6 GB.
  3269 BIOS files (4.1 GB), 5089 game data files (2.5 GB) and 2636 data files (38.5 MB).
  Game data: files a game or a game engine reads, of no use to the other cores. Data files: the files an emulator reads from a data folder of its own, such as Dolphin's Sys and PPSSPP's assets.
  BIOS folder: /home/me/.config/retroarch/system
  106 files read from RetroArch's save directory go to a folder per core under /home/me/.config/retroarch/saves
  Enter) install everything
  c) choose systems, cores and regions
  f) copy from a folder or an old card
  g) Game data: kept (5089 files, 2.5 GB): leave it out
  q) quit
>
  Counted again for your choices. Nothing is written before Enter.

RetroArch: 5905 files, 4.1 GB.
  3269 BIOS files (4.1 GB) and 2636 data files (38.5 MB). 5089 game data files left out.

A list that marks its game data counts three kinds of file apart, on the plan, in this menu and on the result (Installed: 3269 BIOS files, 5089 game data files and 2636 data files.), the parts adding up to the total: BIOS files, game data, and the data files of an emulator's own data folder (Dolphin's Sys, PPSSPP's assets). What the last two are is said once, under the counts. g leaves the game data of the choice out, as --no-game-data does, and counts again (g then keeps it). The plan screen has the same choice as a row of its own, Game data: kept with its count, one press toggling it to Game data: left out, and Options keeps its Game data row too. Its count follows the systems chosen, as g counts them, and a choice that holds no game data has no row. Given --no-game-data, neither the menu nor the plan offers the game data back.

i) only what the installed cores read: 87 files, 43.8 MB appears for RetroArch, Lakka and RetroPie when cores are found installed, here 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. The letter names the lists it asks (c) choose systems with a MiSTer pack), and a list with one answer is not asked.

• Systems. The consoles and computers the platform declares, titled and ordered as the full screen's Choose systems lists them, the id --system takes after each title. A last entry, Other systems and game engines, 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.

Nothing is written yet: the menu comes back counted for the choice, as the full screen's Confirm does, with the command that makes the same choice without questions, every other option of the run in it, for instance python3 install.py --platform retroarch --dest /home/me/.config/retroarch/system --system sony-playstation --region north-america. Enter then installs, and c chooses again.

An option is refused by the axis the list does not record, with what works instead. The MinUI, NextUI and MyMinUI lists record cores and regions and no system: --core and --region narrow them, --system is refused with Run it without --system, or narrow with --core and --region. A pack records the systems of its files and what its platform's list narrows by: with the pack alone, --core or --region names that list (--manifest FILE, a copy of install/minui.json) only when it records them, and MiSTer FPGA's pack says its list records no cores. A list from an older release records none of the three, and the one-line installer fetches the current one.

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):

  2436 game data files left out (--no-game-data): 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 whose system_directory is the BIOS folder, found the same way with --dest or without, cores/ beside RetroArch when the setting is unset, a retroarch.cfg next to the system directory for a portable install, 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. A system --list-platforms names under its own files (muos, arkos) stands for the file list it gets, and the run says which. Unknown names are refused with the closest ones
--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, except for a system that runs from its SD card, which refuses it. 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, and the title a system is printed with is taken too. A short name the platform does not use (gba, psx) is refused with the ids it may stand for, never taken in their place. So is an id the list files under another one: RetroArch keeps neogeo.zip under arcade, which --system snk-neogeo suggests
--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
--declared-only	Keep only the files the platform's own list names (cores: null in the manifest), not the extra files cores load. With --check, the answer is about the list the platform itself checks. Refused with --core, the listings it does not change, --standalone-copies and --tui
--list-systems	Print a platform's systems with the files and size each holds, the files other systems share too counted apart
--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. A run whose output goes to a file or a pipe asks nothing either, and says so on stderr. It finds the setups and the mounted cards the screen finds: one is taken, as Enter takes it, two stop the run with an error event (stage detect, reason conflict) naming each with its --platform and --dest, and none stops it too, with reason not_found when a file list or a pack names the platform
--check	Report and exit without writing
--dry-run	Show what would be downloaded, the totals first, then by system and with sizes, without writing anything. A plan taller than the screen names the ten largest systems, and --verbose lists every system and file
--yes, -y	Do not ask before a download of 1 GB or more, nor anything else. Implies --no-input, so a run that needs an answer (nothing found here, a file list or a pack naming its platform included, or two setups found) stops on what to name instead. --platform names a setup, whose usual folder is then taken
--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
--from FOLDER	Copy the BIOS files a folder holds (an old SD card, a backup, a ZIP) instead of downloading them, each one recognised by its hash and copied, never moved. Repeat for several folders. See Copy from an old card
--from-pack PATH	Install from a pack already downloaded: its ZIP, one of its parts (the others are found in the same folder), or the folder holding them. Makes no network request and checks every file's hash. See Without a network
--offline	Make no network request. --check, --from, --from-pack and --manifest work without one, the file list stops the run at once when none of them gives it, and a file the run would download fails at once. RETROBIOS_INSTALL_OFFLINE=1 does the same. Refused with --target and --list-targets, which read a core list from the network
--manifest FILE	Read the file list from FILE, a copy of install/<platform>.json, instead of downloading it. See Without a network
--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
--tui	Open the full-screen interface, or stop with the reason it cannot open here (code 2) instead of falling back to the questions. Wins over RETROBIOS_PLAIN and ACCESSIBLE. See The full-screen interface
--plain	Ask the questions line by line instead of the full-screen interface, the mode for a screen reader. See The full-screen interface
--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
--add-app	After the install, put the RetroBIOS app on the handheld card the BIOS folder is on (muOS, KNULLI, ROCKNIX), to check and update the BIOS files from the console later. Refused (code 2) for a folder on no such card, and with --check, --dry-run, a listing, --from-pack and --offline. See On a handheld
--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 missing ones whose reason it found, then the first ten other missing ones (--verbose lists them all). See Why a file is refused. --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, NextUI or MyMinUI, as the first line of the card's .system/version.txt names it	MinUI, NextUI or MyMinUI	the card root, below which the list writes Bios/<tag>/. Without version.txt the three cannot be told apart: named, not installed to, and the message gives --platform and --dest to use
/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.

A card that holds a system's own files is read the same way, without --platform or with the one that names its list, by the rules the table above gives for the device, below the card's root instead of its mount point:

On the card	System	Files go to
system/configs/emulationstation/about.info holding the line KNULLI	KNULLI	bios, KNULLI's list
system/batocera.conf holding the line system.hostname=KNULLI	KNULLI	bios, KNULLI's list
.config/system/configs/system.cfg holding the line root.password=rocknix	ROCKNIX	roms/bios, ROCKNIX's list
MUOS/	muOS	MUOS/bios, RetroArch's list
spruce/	spruceOS	BIOS, RetroArch's list
System/usr/trimui/crossmix-version.txt	CrossMix-OS	BIOS, RetroArch's list
.tmp_update/onionVersion/version.txt	Onion	BIOS, RetroArch's list
.allium/	Allium	BIOS, RetroArch's list
Koriki/version.txt	Koriki	BIOS, RetroArch's list
system/batocera.conf holding system.hostname=BATOCERA or no hostname line, and no KNULLI file above	Batocera SHARE drive	bios, Batocera's list
system/recalbox.conf	Recalbox SHARE drive	bios, Recalbox's list
system/batocera.conf with any other hostname, and no KNULLI file above, or the files of two SHARE drives	named by neither: the run says which systems it could be	the folder of the system named with --platform

Each file is one the system writes. KNULLI is read by about.info first, which no menu writes: its HOSTNAME row rewrites system.hostname, and a KNULLI card renamed there was read as a Batocera SHARE drive. ROCKNIX's line changes with its root password, and a card whose password was changed is named by nothing, never by another system. A drive whose files fit two systems is named by neither: the first screen and --plain say which systems it could be and the two commands that name it, and a --dest named with one of them takes it as that system's, with a note. The full screen lists it under each system it could be ("KNULLI2: if it is a KNULLI card"), and with a file list for one of them it is that system's card, offered first, never "no card is mounted". --plain numbers it the same way ("Type 1 if it is the KNULLI card").

The full screen lists such a card on its first screen ("muOS SD card (E:)"), and a SHARE drive the same way ("Batocera SHARE drive (SHARE)"): its root, typed or given with --dest, stands for its bios folder. Two cards of one system say what their BIOS folder holds ("Onion SD card (OLDONION, 6 BIOS files)"), the one holding fewer first. Named by its system (--platform muos, --platform knulli), a --dest that is another system's card is refused, and so is another system's SHARE drive for Batocera and Recalbox. One that holds none of the system's files is refused where the card always carries them. For KNULLI, ROCKNIX and the systems no file on the card names, it gets the system's folder below it (bios, roms/bios), with a note. Named with a file list instead (--platform batocera --dest an Onion card), another system's card takes the files as named, and a note names the system and its folder.

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. With nothing found, the folder question offers both usual folders of a setup that has one on each side: RetroArch's in this Linux (~/.config/retroarch/system, under Enter) and the Windows one (C:\RetroArch-Win64\system), each named by its side.

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), /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.

The systems that run from an SD card keep their files there: MinUI, NextUI, MyMinUI, KNULLI, ROCKNIX, AmberELEC and EmuELEC (the card's games part, which they mount as /storage/roms), and each system of the Linux handhelds that gets RetroArch's list (Onion, muOS, spruceOS, ArkOS, UnofficialOS and the others). Run on the device, the installer finds its folder. From a computer, each has a row of its own in the setup list (Onion, SD card), without the filter, and in the --plain menu, beside the devices that run it (Miyoo Mini, Miyoo Mini Plus). The filter takes a device name, and so does the --plain menu, which lists the setups it matches by number. With nothing found here, the SD card rows come right after RetroArch: Onion comes into view after five presses of L1 and R1 at 40x12, where it was row 30 of 34. That row, --platform onion and the menu all ask for the card: one card of that system mounted when the run starts is taken, otherwise the screen opens Where is the SD card?, which lists only that system's cards and offers Look again, and --plain asks Card root, listing the same cards by number and naming the one picked and its folder. The RetroArch row is this computer's RetroArch.

The card's top folder is read by one function wherever it is chosen, listed, browsed, typed, numbered or named with --dest, and gives the same folder and the same note on the screen and in --plain. A folder that does not exist, or that is another system's card, is refused for every system, and so is a folder inside another system's card (ROCKNIX's roms/bios named for KNULLI). A card whose own files name it is that card whatever its name: an Onion card mounted as BIOS gets BIOS/BIOS. One without the system's own files is refused for the MinUI family, Onion, muOS, spruceOS, CrossMix-OS, Allium and Koriki. KNULLI and ROCKNIX fill their card when they first start, and no file on the card names ArkOS, dArkOS, JELOS, KOLOS, UnofficialOS, ArchR, RetroOZ, plumOS, MiyooCFW, AmberELEC, EmuELEC or the Anbernic firmware: such a folder gets the system's folder below it, and a note says so, kept on Create the folder? and the plan. No to creating its folders asks for the card again. Under WSL a drive letter (D:, D:\) is that Windows drive, typed or given to --dest, --from, --from-pack, --save-dir and --cores-dir, and the screens write the folder D:\BIOS. Without questions (--no-input) the run stops with a --dest example. A --dest that is a folder inside a MinUI card (its Bios/) is refused with the root to name instead. A refused --dest ends with code 1 and an error event (stage detect). 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. When detection met a folder this user cannot open, under the home folder or above the default, no default is taken: the frontend's own configuration there may name another folder, so the run asks for --dest.

With nothing detected, the setup screen lists the platforms to choose from, and --plain gives the same list numbered, in the same order, with --dest too. Both find the SD cards mounted here, the screen under Found on this machine. With a setup found, the setup screen lists it with Another setup or folder, and --plain asks the same: Enter takes the first, o opens the numbered list and then the folder, q quits. A platform named and found nowhere gets its folder asked, its usual one under Enter, the mounted drives numbered. A list or a pack read by card setups too (RetroArch's, read by Onion, muOS, ArkOS and the others) opens the setup list instead, filtered to the setups that read it, RetroArch first: Enter on it asks RetroArch's folder. At that question a drive is numbered by the folder its system reads (ONION: BIOS), a drive nothing names by its bios folder (EASYROMS: bios), never by its root, which no setup reads. A handheld's card whose own files sit on a part a computer does not open is told by the folders its system writes beside bios on the games part: themes and launchimages on ArkOS's EASYROMS, gamedata and homebrew on AmberELEC's GAMES, bezels/default.cfg on EmuELEC's EEROMS. A disk Windows or Linux calls fixed is never one. With nothing found here the first screen and line mode say A card is in the reader (EASYROMS): choose its system (two cards: choose their systems), and its bios folder comes first at the folder question, under Enter, before this computer's usual folder. A drive with a bios folder and none of those folders, a data drive or a stick, is numbered with a note (DATA has a bios folder, and nothing on it shows a handheld's card: listed, not chosen.) and never taken under Enter. Another system's card or SHARE drive, and a drive two systems fit, are left out, and a line names them: each is reached through its own setup. A folder typed is read from the current one when it is not a full path, and named in full after. q quits there too (a folder named q is typed ./q), and Enter with no default says what to type. On a computer Batocera and Recalbox have no default: the drives are numbered by their bios folder (SHARE: bios), as the screen lists them, and a drive whose files name another system is left out. Without questions the run stops there with an error event and a --dest example. A device several systems run lists them all, and a model finds the systems that list its family (RG353V finds ROCKNIX, which lists RG353). Both 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://abdess.github.io/retrobios/i | 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

RetroBIOS also runs on the handheld itself, in the full-screen interface, with the controller. Copy the file for your system to the SD card, then start RetroBIOS from the menu.

The files below ship with the next release. Until then, build them from a clone of the repository with python scripts/build_port.py, which writes all four into dist/, or use the computer route at the end of this section.

System	File	Copy it to	Start it from
muOS	RetroBIOS.muxapp	ARCHIVE at the root of the card, then install it from the Archive Manager	Applications
Any other system with PortMaster: ArkOS, dArkOS, ROCKNIX, AmberELEC, JELOS, Knulli	RetroBIOS.zip	PortMaster's autoinstall folder: /roms/ports/PortMaster/autoinstall/ on ROCKNIX and AmberELEC, /roms/tools/PortMaster/autoinstall/ on ArkOS, /userdata/system/.local/share/PortMaster/autoinstall/ on Knulli	Ports, after opening PortMaster once
Batocera, Knulli	RetroBIOS-batocera.zip, extracted	roms/ports on the SHARE partition	Ports, after updating the game list
ArkOS, dArkOS	RetroBIOS-tools.zip, extracted	tools on the EASYROMS partition	Options, then Tools
ROCKNIX, JELOS	RetroBIOS-tools.zip, extracted	/storage/.config/modules, over the network share or SSH	Tools
AmberELEC	RetroBIOS-tools.zip, extracted	/storage/.config/distribution/modules	Tools

RetroBIOS.zip also installs on muOS, from MUOS/PortMaster/autoinstall/ on the first card (/mnt/mmc on the device). It then shows the interface in muxterm, as the muOS app does.

Button	Action
D-pad	Move
A, Start	Choose, continue
B, Select	Back, and quit on the first screen
X	Tick or untick a system
Y	Options
L1, R1	Page up, page down (not in muxterm, which keeps them for its own scrollback)
Hold Select, then Start	Quit at once (PortMaster port, muOS, Tools)

Start pressed first also chooses the line in focus: hold Select first. A running install is then stopped the way B stops it, and the last screen says what it wrote. On muOS without PortMaster, muxterm reads the pad itself: Y ticks a system, Select shows its keyboard, and Menu quits. L1 and R1 do not page there: muxterm keeps PgUp and PgDn for its own scrollback, so Left and Right on the D-pad page a list instead, as they do with gptokeyb in muxterm.

Each launcher also sets RETROBIOS_IDLE_EXIT to 300: with no button pressed for 5 minutes since it opened, and no check or install running, the interface closes by itself. A pad the system has no mapping for sends nothing, and would otherwise leave the console stuck on the interface with no way out. It closes with RetroBIOS: No button pressed, closing. and exit status 2, as a quit before the install. Closed on an error or a result screen, it prints that screen's words after the line and exits with its code (1 for No internet: offline mode), so the launcher can tell an error from a close with nothing to report. The time counts from the end of the last check, so a launcher that names the platform, whose interface moves on to the plan by itself, closes the same way. Any launcher can set it to another number of seconds.

Each launcher tells the interface which buttons reach it, in RETROBIOS_PAD, so the hints can name them:

Value	Input	Set by
gptokeyb	gptokeyb or gptokeyb2 with retrobios.gptk, the table above	the PortMaster port and the Tools entry
gptokeyb_muxterm	the same, inside muxterm, which keeps L1 and R1 for its scrollback: Left and Right page	the muOS app with PortMaster
muxterm	muxterm's own keys: D-pad (Left and Right page), Start as Enter, B as Backspace, Y as Space	the muOS app without PortMaster
evmapy	RetroBIOS.sh.keys, the same buttons as the table	the Batocera and Knulli port
miyoo	buttons that are already keys: A as Space, Start as Enter, L1 and R1 as E and T, L2 as Tab, R2 as Backspace	no launcher yet

A launcher with no mapper at all (a keyboard) leaves it unset.

The help screen (?) names the keys of the route in use. A computer gets the keyboard column, and SteamOS game mode or a console no launcher named gets the column that names both:

Action	Computer (keys)	Unknown (both)	gptokeyb	gptokeyb_muxterm	muxterm	evmapy	miyoo
Move	Up/Down, k/j	Up/Down, k/j	D-pad, Up/Down	D-pad, Up/Down	D-pad, Up/Down	D-pad, Up/Down	D-pad, Up/Down
Page	PgUp/PgDn	PgUp/PgDn, L1/R1	L1/R1, PgUp/PgDn	D-pad Left/Right	D-pad Left/Right	L1/R1, PgUp/PgDn	L1/R1, PgUp/PgDn
Continue, open, choose	Enter	A/Enter, Start	A, Start, Enter	A, Start, Enter	Start, Enter	A, Start, Enter	A, Start, Enter
Tick, untick	Space, Right/Left	X, Space, Right/Left	X, Space, Right/Left	X, Space	Y, Space	X, Space, Right/Left	A, Space, Right/Left
Options	o, Tab	Y, o, Tab	Y, Tab, o	Y, Tab, o	o, Tab	Y, Tab, o	L2, Tab, o
Back, and quit on the first screen	Esc, Backspace	B/Esc, Backspace	B, Select, Esc	B, Select, Esc	B, Esc, Backspace	B, Select, Esc	R2, Esc, Backspace
Stop an install	Esc, Ctrl-C	B/Esc, Ctrl-C	B, Esc, Ctrl-C	B, Esc, Ctrl-C	B, Esc, Ctrl-C	B, Esc, Ctrl-C	R2, Esc, Ctrl-C
Quit at once	none	Select+Start	Select, then Start	Select, then Start	none	none	none
Use the folder typed	Enter	Enter	A, Enter	A, Enter	Start, Enter	A, Enter	Start, Enter
Clear a filter, leave the folder typed	Esc	Esc	B, Esc	B, Esc	Esc	B, Esc	Esc

On a Miyoo, B, X, Y and Select are Left Ctrl, Shift, Alt and Right Ctrl: pressed alone, a modifier sends nothing to a terminal, so the interface goes back with R2 instead, and the bottom line says so.

Without Wi-Fi. On a computer, download the BIOS pack that serves your system (every part, for a pack in parts): RetroArch's on muOS, ArkOS, dArkOS and JELOS, Batocera's on Batocera. Copy it next to RetroBIOS: into ports/retrobios for the PortMaster port and on Batocera, to the root of either card on muOS, into the retrobios folder of the Tools entry. With no connection, RetroBIOS installs from it, as --from-pack does. With no pack there, it names the pack and the folder. The releases carry no pack for ROCKNIX, Knulli or AmberELEC: there RetroBIOS needs Wi-Fi, or the computer route.

On a two-card device, RetroBIOS without Wi-Fi first asks to copy the BIOS files from your other card: muOS's MUOS/bios on the card the system does not read, or the other of /roms/bios and /roms2/bios on ArkOS and dArkOS. A says yes, as --from does. The list of files still comes from the pack, so the pack is needed too.

What it needs. Python 3.8 or newer: the system's, else PortMaster's python_3.11 runtime on aarch64, which the PortMaster port downloads on first use and the Tools entry then reuses. That runtime uses the system's OpenSSL 1.1, so on an image with OpenSSL 3 only it may not download (not tried on a device). The BIOS folder must be one the installer detects, see Platform detection. On a read-only or full card, RetroBIOS keeps its log in retrobios under XDG_RUNTIME_DIR or /tmp, and the interface names the folder it cannot write.

Where no terminal shows. The PortMaster port draws on the console, or in foot or xterm under a desktop session. Where neither can, it opens PortMaster's own screens instead: the same check, update and choice of systems, one list at a time. On Batocera and Knulli the visible terminal is not verified on a device yet: RetroBIOS tries xterm or foot, then console 4, and stops when console 4 does not come to the front. retrobios/log.txt names each route it tried, and log.prev.txt keeps the run before.

From a computer. Onion, MinUI, NextUI, Allium, GarlicOS and the Switch have no Python 3 to run the installer. Put the card in a computer and run the one-line command there: it finds a mounted Onion, spruceOS, MinUI, muOS, Knulli or ROCKNIX card by itself. For a card it does not recognise, add --platform <platform> --dest <BIOS folder on the card>. This works for every system above too.

The app, from a computer. After an install on a muOS, KNULLI or ROCKNIX card, the installer can put RetroBIOS on that card too, so the console checks and updates its BIOS files later. The result screen offers Put RetroBIOS on this card (update from the console later), Options has the same row, the line questions ask once ([y/N]), and a script adds --add-app. Nothing is written without that choice.

System	Written on the card	Then, on the console
muOS	ARCHIVE/RetroBIOS.muxapp, which the Archive Manager lists	install it from the Archive Manager, start it from Applications
KNULLI	roms/ports/RetroBIOS.sh, RetroBIOS.sh.keys and the retrobios folder, on the SHARE partition	update the game list, start it from Ports
ROCKNIX	.config/modules/RetroBIOS.sh, executable, and the retrobios folder, on the STORAGE partition	start it from Tools

The files are the launchers above, from the same ref as the file lists: install/launchers/index.json lists each one with its size and SHA-256, and every file is fetched and checked before the first is written. The muOS archive holds the members of RetroBIOS.muxapp, stored rather than compressed, and is checked against the hash the list records for it. A file already in place with that content is left alone, so a second run writes nothing. A different one is moved to retrobios-backup first, as a BIOS file is. Onion, MinUI, NextUI, MyMinUI and Allium have no Python to run it, and the result says so in one line. spruceOS and CrossMix have no launcher yet. With --from-pack or --offline the app is not offered, the launchers coming from the network.

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. The copies the site serves name the commit's install.py, which never changes, and both downloaders stop on a cut transfer before the hash is read: there a mismatch is a file changed on its way, by a proxy or an antivirus, and that is what they say. The raw form reads main, whose two files can come from caches a few minutes apart right after an update: it says to try again, and that waiting five minutes settles it. The site build refuses to publish a copy whose pin is not the SHA-256 of the install.py it names, and Deploy Site runs the bootstrap tests before it deploys, so a failed check keeps the last good pair served. 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 or any other control character, a doubled separator, a trailing slash and any .. component, so a destination cannot climb out of the BIOS directory and no file is named with a terminal command. 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.

Every other string from outside is shown, never obeyed: the names a list or a pack records, a card's label and a folder a configuration names reach the terminal, line by line or on the screen, and the --events stream with a ? for each control character. A folder a configuration names with one is not taken: the run says so and asks for --dest, its default being no answer for a setup that reads another folder.

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 way to install is the command run on a computer with the Pi's network folder as --dest (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.

The tables of options, events, exit codes and keys on this page sit between generated markers and are written from install.py by scripts/generate_installer_doc.py: the options from its parser, the events from EVENT_KEYS, the codes from its sys.exit calls, the keys from TUI_ROUTES. The prose cells stay as written. A row the code gains stops the script until its text is added inside the markers, and --check, which a test runs, fails on a table behind the code. --page FILE renders another copy of the page, which the tests use.

The handheld archives each carry install.py, the one the one-line command of the same commit downloads: scripts/build_port.py refuses any other (it compares it with the SHA-256 install.sh pins). The file lists come from main. The launchers in ports/ start it with --tui, and read it through Machine-readable events for the rest.

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 or were left out by --offline while others installed, --check found files to fetch, a --from-pack pack that cannot be read, lacks a part or is for another platform, a --from folder that does not exist or cannot be read, a --dest that is not the card of the system named (another system's card, a folder inside one, a drive with none of its files where its card always has them, or a folder that does not exist), --restore could not put a file back, or --add-app could not put every file of the app on the card
2	nothing was installed: every file the run tried failed (a BIOS folder that cannot be written, for one), or --offline left every file out, the drive has too little free space for the download (checked before any folder is created), or the question about a folder that does not exist, named with --dest or typed at the folder question, was answered no. Also an option the installer refused before any download: an unknown option, --jobs outside 1 to 32, --target with --every-board or --from-pack, --target or --list-targets with --offline (or RETROBIOS_INSTALL_OFFLINE set), which read a core list from the network, --add-app with --check, --dry-run, a listing, --from-pack or --offline. The message then starts with install.py: error:. Also --add-app for a folder on no card that takes the app, said in an Error: line and an app event before anything is written. With --restore, a folder that is not a dated folder inside retrobios-backup. Also a quit chosen before the install, as gh ends a cancelled prompt: q at a question, q or Quit on the full screen, which then keeps RetroBIOS: quit. Nothing was installed., and the full screen closed with no button pressed (RETROBIOS_IDLE_EXIT). No code but 0 closes a Windows Terminal tab started on the installer itself, so such a tab stays open on a quit
130	stopped with Ctrl+C, or with Ctrl+C or Ctrl+D at a question, the terminal keeping RetroBIOS: stopped. Nothing was installed. before an install. Run the same command again to carry on
141	the output was piped to a reader that closed early (--list-platforms | head)

The full screen ended by SIGTERM (Select+Start on a handheld) before any install exits 143. During an install it stops the install first, and exits 130. Its window or terminal closed (SIGHUP) exits 129, during an install too: the install is stopped as Ctrl+C stops it, and the last lines go nowhere, no one being left to read them.

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.

To tell missing files from a failure, read the check event of Machine-readable events: missing and wrong_hash count what is left.

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 this table is written from it. The same keys, with their types, are in schemas/install-events.schema.json, written from EVENT_KEYS by scripts/generate_event_schema.py and published with the other schemas under api/v1/schemas/.

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
unsearched	folder, reason, message	Before detect, once for each folder the search for setups could not look in, this user being refused it. What it would hold counts as absent, and the other places are still searched: detect then lists what they hold, and an empty platforms after an unsearched line means nothing was found where the installer could look. reason says why in words (Permission denied), message says it in a sentence
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, clock when the server's certificate was refused and the system clock reads a date before the installer was written, no_ca when the machine holds no list of trusted certificates (SSL_CERT_FILE names one), or offline when --offline forbids the request. A folder named with --from cannot be read (stage is from, reason not_found, not_a_folder for a file that is no ZIP, unreadable, or system for the root of the system, /proc, /sys or /dev). The BIOS folder sits under a folder this user cannot open (stage is dest, reason unreadable), and the run ends with code 1 before anything is written. The BIOS folder cannot be created (stage is dest, reason not_writable): a summary follows with what the run installed before it. Two systems are detected on one machine and no --dest names the folder (stage is detect, reason conflict). The platform named with --platform is found nowhere and no folder can be assumed for it: a card system with no card named, a portable emulator, Batocera or Recalbox named on a computer (their folder is the bios folder of their SHARE drive), or no usual folder on this system or one set aside behind a folder this user cannot open (stage is detect, reason not_found). So is a platform named by a file list or a pack, in a run without questions where it is found nowhere here. A --dest refused as the card of the system named carries the same stage and reason: another system's card, a folder inside a card, a drive with none of the files its card always has, or a folder that does not exist. message says it in words, and is the only thing that tells these cases apart
scanned	folder, files, truncated, other_drives	Each folder named with --from, once read and before detect. files counts the files found, truncated is true when the search stopped at 200,000 of them, and other_drives lists the folders below it on another drive, which were not entered
version	platform, list_version, installed_version, message	Before choices, when the system here runs another version than the one the list was built for: list_version is the list's, installed_version the one the system's version file states, and message says it and what it means. Not written when either version is unknown. The run goes on
choices	platform, systems	Before checking: the systems the run's list lets one choose among, sorted by id, other last for the files no system names. The run's other options apply (--core, --region, --no-game-data, the files left out for an unknown save directory), --system does not: these are the systems a screen lists to choose from, and the count a --system is out of
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, and with --system only the systems named. Files with no system count under other. name is the platform's own name for it
checking	files_done, files_total	While the files already in the folder are read and hashed, at most every half second and once at the end. files_total counts the files found in place
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
declared	platform, files, present, missing, wrong_hash, bytes_needed, dests	Right after check, the same counts over the files the platform's own list names (cores: null), and their dests in the order of the file events. A setup that checks its own list reads its answer here, with or without --declared-only
data	platform, files, bytes	Right after declared: the data-tree files to fetch (the data_missing of check) and the bytes they write once in place
found	platform, dest, folder, path, member, reason	Each file to install that this machine already holds, after check and before anything is written, in --check and --dry-run too. folder is the --from folder as given, or the bios_dir of the check when the BIOS folder holds the file at another place, and then reason says where in words (nested folder: ... for a misplaced file, the same file is at ... for one the list installs there too). path is the file, and member the ZIP member holding the bytes when path is an archive, an empty string otherwise. Its copy is reported by a downloaded event
unreadable	platform, folder, path, member, reason	Each file in a --from folder that could not be read and may be one the run still needs, right after the found events: its size is that of a file no copy was found for, or unknown (a folder that could not be listed, a ZIP that would not open). member names the ZIP member, or is empty. reason says why in words (Permission denied, it is encrypted, a password is needed)
saves	platform, files, folder	After choices and before checking, when the files the run installs (once --system and the other choices narrowed the list) hold some read from the frontend's save directory and that directory is known: how many, and the folder they go to, where <system> and <core> stand for one folder per system or per core (the screen and --plain say it in words: "a folder per core under /sdcard/RetroArch/saves"). When it is not known, the files are counted in the summary's skipped instead (no_save_directory)
download	platform, files, bytes	Before the downloads start. Counts the files copied from this machine too
progress	files_done, files_total, bytes_done, bytes_total	At most every half second while bytes arrive
transfer	bytes_local, bytes_network	Right after each progress event, and once when the files of a download event are done. It splits bytes_done: bytes_local came from this machine (a copy found by --from or in the BIOS folder, the pack, a partial copy resumed), bytes_network from the network. A download speed is bytes_network over the time elapsed
downloaded	dest, ok, reason, size, files_done, files_total, bytes_done, bytes_total	Each finished file, downloaded or copied from where a found event named it. 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
app	system, folder, ok, reason, dests, written, kept	After summary, with --add-app or a yes to its question: the RetroBIOS app on the card of system whose root is folder. dests lists the app's files below that root, written the ones this run wrote (empty when each was in place), kept the backup folders as in summary. ok is false, with reason, when the card takes no app (before anything is written, code 2), when the install did not finish, or when a file could not be fetched, verified or written (code 1)
end	code	Last line, with the exit status the process returns (see Exit status)

Schema 1 can gain a kind (found came with --from, declared with --declared-only, unsearched with the search that goes on past a closed folder, app with --add-app, data with the size of the data trees, version with the list's version), never a key of an existing kind: a reader skips a kind it does not know. 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, or as a crash: an error the installer did not expect ends the process on a Python traceback, on standard error, without an end line.

Five lines of a run of --check --events --system sony-playstation on a RetroArch folder that holds only scph5501.bin, in the order written:

{"event": "start", "schema": 1, "installer": "c90676dcc433", "mode": "check"}
{"event": "file", "platform": "retroarch", "dest": "scph5501.bin", "systems": ["sony-playstation"], "size": 524288, "state": "present"}
{"event": "check", "platform": "retroarch", "name": "RetroArch", "bios_dir": "system", "files": 118, "present": 1, "missing": 117, "wrong_hash": 0, "bytes_needed": 344457216, "data_missing": 0, "not_installable": 0}
{"event": "summary", "mode": "check", "installed": 0, "up_to_date": 1, "pending": 117, "failed": [], "skipped": [], "left_out": [], "kept": [], "interrupted": false}
{"event": "end", "code": 1}

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_INSTALL_OFFLINE	Set to anything but 0: no network request, as with --offline. The runs the full-screen interface starts inherit it. The words then name the variable (not fetched (RETROBIOS_INSTALL_OFFLINE=1), run it with RETROBIOS_INSTALL_OFFLINE unset), and --offline where the option was given. RETROBIOS_OFFLINE is the build scripts' own and leaves the installer alone
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, when set to any value but an empty one. TERM=dumb, or no TERM outside Windows, also turns the live progress line and the colour off, as does a terminal whose description moves no cursor the ANSI way (TERM=vt52). A description naming fewer than 8 colours keeps the live line and drops the colour. The full screen then draws the same text without colour: the row in focus is marked with > as well as reverse video, and every state is written in words
TERM, TERMINFO, TERMINFO_DIRS	Decide whether the full screen opens. TERM unset or dumb (outside Windows) gives the questions line by line. Otherwise the terminal's description is read where ncurses reads it: TERMINFO, then ~/.terminfo, then each folder of TERMINFO_DIRS, then the system's own. A description whose cursor moves are not the ANSI ones the screen writes (TERM=vt52) gives the questions too, and --tui there stops with the reason
FORCE_COLOR, CLICOLOR_FORCE	Colour even when the output is a pipe or a file, set to any value but 0 or an empty one. NO_COLOR wins over both, and the progress line stays one line per file
SSL_CERT_FILE, SSL_CERT_DIR	The trusted certificates to check servers with, for a Python that finds none of its own
RETROBIOS_PLAIN, ACCESSIBLE	Set to anything but 0: the questions come line by line, as with --plain, instead of the full-screen interface
RETROBIOS_PAD	The buttons a handheld launcher's mapper sends to the full screen (gptokeyb, gptokeyb_muxterm, muxterm, evmapy, miyoo), so its hints name them. See On a handheld
RETROBIOS_IDLE_EXIT	Seconds the full screen waits for a first button, counted while nothing runs. With none pressed, it closes with exit status 2, as a quit, or with the code of the error or result screen it closed on
RETROBIOS_NO_MOUSE	Set to any value but 0 or an empty one: the full screen never asks the terminal for clicks, and the mouse selects text everywhere as it does outside the installer
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 connection that does not open within 4 seconds counts as none, so a dropped network gives its error in about 15 seconds. Once a connection is open, a slow transfer keeps the full timeout. The file list is the exception: a server that takes the connection and then sends nothing (a Wi-Fi sign-in page, a stuck proxy) gets 15 seconds per wait and two attempts, about 30 seconds in all. A file that fails three attempts is counted and reported at the end, and the next run fetches only what is still missing.

The reason is said in words: no internet connection or a name that could not be looked up, a connection that timed out, was refused or was cut, a certificate that was rejected. --verbose adds the text Python gave. Two causes are not the network and are not retried:

• The clock reads 1980-01-01: a device without a clock battery starts on an old date, and every certificate then looks not yet valid. Connect to Wi-Fi and let the time sync, or set the date, then run again.
• This system has no list of trusted certificates: install the ca-certificates package, or name a certificate bundle with SSL_CERT_FILE. When the system keeps one where this Python does not look, the message names it. Certificate checks are never turned off.

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.

When a folder above the BIOS folder cannot be opened at all (/root/... run without sudo, a card mounted for another user), the run stops before it starts: this user cannot open /root (Permission denied), which holds /root/.config/retroarch/system. The full-screen interface says the same on the folder screen and asks for another folder.

A folder the search for setups cannot open (~/.config/EmuDeck left to root by a sudo run) is named once, Could not look for setups: this user cannot open ..., and the search goes on everywhere else: a RetroArch whose retroarch.cfg is readable is still found at the folder it reads. The full-screen interface keeps that line above the list of setups.

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://abdess.github.io/retrobios/i | sh -s -- --platform retroarch --dest ~/.config/retroarch/system
curl -fsSL https://abdess.github.io/retrobios/i | sh -s -- --platform batocera --dest /userdata/bios

&([scriptblock]::Create((irm https://abdess.github.io/retrobios/i.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. Later releases publish packs only for the setups most people download, so Lakka, which runs on Linux where two names that differ by case are two files, is served by the installer. The download scripts name the installer for a setup without a pack.

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, and each part leaves a marker file naming every part, which --check reads to name a part that is missing. 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.