Filament

A single-file USB tool for Linux
TUI • CLI • Write • Format • Wipe

No build system. No headers. No surprises.

What it is • Features • Quick start • CLI • Safety • Requirements

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What it is

Filament writes ISO images to USB drives, formats drives as FAT32/exFAT, and wipes drives. One C file. TUI or CLI. libc and ncurses, nothing else.

It refuses to touch mounted devices or any disk with a system mount. It makes you type the device name before anything destructive. It tells you when the kernel is still buffering writes instead of inventing a speed number.

Features

• Write ISO images: raw write, configurable block size, progress, speed, ETA
• Verify after write: byte-for-byte, mandatory unless --no-verify
• SHA-256 hashing: optional, off by default, source and target
• Compressed sources: .gz, .xz, .bz2, .zst decompressed on the fly
• Format: FAT32, VFAT, exFAT
• Partition tables: MBR, GPT
• Quick wipe: first 1 MB
• Full zero: entire device
• Safety checks: refuses mounted devices and system disks
• Device name confirmation for anything destructive
• Filesystem detection: FAT32, exFAT, NTFS, ext; partition table type
• Multi-device listing of removable USB devices
• File browser with hidden-file toggle
• Full CLI mode
• Scripting flags: --yes, --quiet, --log=FILE
• Source hash verification against a .sha256 file before writing
• SIGINT handling
• Honest progress: buffering... until writes block, then real device speed

Quick start

gcc -std=c99 -Wall -Wextra -pedantic -O2 -o filament filament.c -lncurses
sudo ./filament

TUI

Main menu

Key	Action
1	Write ISO to USB
2	Format USB
3	Wipe/zero USB
4 / Q	Quit

Device selection

Key	Action
↑ / ↓	Navigate
Enter	Select
Q	Back

File browser

Key	Action
↑ / ↓	Navigate
Enter	Open / select
Backspace	Parent directory
H	Toggle hidden files
Q	Cancel

Confirm write

Key	Action
V	Toggle SHA-256 output
Enter	Confirm (asks for device name)
Backspace	Back
Q	Cancel

Format options

Key	Action
F	Cycle filesystem (FAT32 / VFAT / exFAT)
T	Toggle partition table (MBR / GPT)
L	Set volume label
Enter	Start (asks for device name)
Backspace	Back

Wipe/zero

Key	Action
Q	Quick wipe (first 1 MB)
F	Full zero
Other	Cancel

Destructive operations require typing the device name (sdb).

CLI

filament --version
filament --help
filament --list
filament --list-partitions /dev/sdb

sudo filament --write /dev/sdb image.iso
sudo filament --write /dev/sdb image.iso --sha256
sudo filament --write /dev/sdb image.iso --no-verify
sudo filament --write /dev/sdb image.iso --dry-run
sudo filament --write /dev/sdb image.iso --unmount
sudo filament --write /dev/sdb image.iso --block-size=1048576
sudo filament --write /dev/sdb image.iso.gz
sudo filament --write /dev/sdb image.iso --verify-source=image.iso.sha256

sudo filament --wipe /dev/sdb
sudo filament --zero /dev/sdb

sudo filament --format /dev/sdb --fat32
sudo filament --format /dev/sdb --exfat --gpt --label=MYUSB

Block size: 4096 to 67108864 bytes.

Global flags

Flag	Effect
--yes	Skip interactive confirmation. Required for non-tty.
--quiet	Suppress progress output.
--log=FILE	Append an audit log.

Destructive CLI operations prompt for yes unless --yes is given.

Slow USB sticks

USB sticks lie. The kernel absorbs writes into page cache at hundreds of MB/s, then dribbles them to flash at whatever the flash can do.

• Speed shows buffering... while the kernel absorbs. No fake number.
• Once writes block, speed switches to (writing) and shows real device speed.
• Verify reads back from the device. Always honest.
• After the write pass, Syncing to Device while the kernel flushes. Slow devices can take a minute. Not a hang. Do not remove the device.

Total wall time is unchanged. Filament just tells you where it went.

Filesystems

Filesystem	Write ISO	Format	Notes
FAT32	✓	✓	Universal, 4 GB file limit
VFAT	—	✓	FAT32 with long names
exFAT	—	✓	Large files, modern systems
NTFS	—	—	Detected, not formattable

External tools

Formatting shells out. Nothing else does.

Operation	Requires
Format FAT32 / VFAT	mkfs.vfat (dosfstools)
Format exFAT	mkfs.exfat (exfatprogs) or mkexfatfs (exfat-utils)

Compressed sources shell out to gzip, xz, bzip2, or zstd. Write, verify, wipe, zero, list, and the TUI do not touch external tools. Missing formatters means formatting fails; everything else works.

Format always unmounts the target first.

Safety

• Mounted device check: refuses anything mounted
• System disk check: refuses any disk with a mount outside /media, /run/media, or /mnt
• Device name confirmation: type sdb before anything destructive (TUI)
• yes prompt in CLI unless --yes is passed
• Dry run: --dry-run shows what would happen
• Clear identification: model, serial, size, filesystem, partition table

Requirements

ncurses for the TUI.

# Artix / Arch
sudo pacman -S ncurses

# Debian / Ubuntu
sudo apt install libncurses-dev

# Fedora
sudo dnf install ncurses-devel

# Void
sudo xbps-install ncurses-devel

Formatting also needs:

# Artix / Arch
sudo pacman -S dosfstools exfatprogs

# Debian / Ubuntu
sudo apt install dosfstools exfatprogs

# Fedora
sudo dnf install dosfstools exfatprogs

# Void
sudo xbps-install dosfstools exfatprogs

Project layout

FILAMENT/
├── filament.c
├── LICENSE
└── README.md

Why Filament Exists

I'll be dead honest here. I fucking hate balenaEtcher, Rufus isn't portable to Linux, and dd reminds me of drinking 2 liters of red wine with not so great outcomes.

Filament is simple, safe, fast, and works. It does one thing well, among a few other things.

Contributing

Single file. Minimal dependencies.

License

CLEAR v1 © realvolk 2026.