fls - The Fast Flash Tool

A high-performance command-line tool for flashing disk images to block devices. fls can download images from URLs, decompress them on-the-fly, and write directly to block devices with optimized buffering and progress reporting.

Features

• Stream-based flashing: Download, decompress, and write in parallel
• Multiple compression formats: Supports .xz, .gz, .bz2, and more
• Progress monitoring: Real-time progress bars for download, decompression, and write operations
• Automatic retries: Built-in retry logic for network failures
• Optimized I/O: Configurable buffer sizes for optimal performance

Installation

From GitHub Releases

Download the latest release for your architecture:

# For ARM64/aarch64 systems
curl -L https://github.com/jumpstarter-dev/fls/releases/download/0.1.5/fls-aarch64-linux -o /usr/local/bin/fls
chmod +x /usr/local/bin/fls

# For x86_64 systems
curl -L https://github.com/jumpstarter-dev/fls/releases/download/0.1.5/fls-x86_64-linux -o /usr/local/bin/fls
chmod +x /usr/local/bin/fls

Replace 0.1.5 with the desired version from the releases page.

From Source

cargo build --release
sudo cp target/release/fls /usr/local/bin/

Usage

Basic Example

Flash a compressed image from a URL to a block device:

fls from-url \
  -k \
  -n \
  "https://example.com/path/to/image.raw.xz" \
  /dev/mmcblk1

Flags used:

• -k - Skip SSL certificate verification (useful for internal servers with self-signed certs)
• -n - Print progress on new lines (better for logging)

Advanced Example

Flash with custom headers and progress interval:

fls from-url \
  --header "Authorization: Bearer token123" \
  --progress-interval 1.0 \
  --buffer-size 2048 \
  "https://cdn.example.com/rhivos-image.raw.xz" \
  /dev/nvme0n1

Example Output

Block flash command:
  URL: https://example.com/path/to/image.raw.xz
  Device: /dev/mmcblk1
  Buffer size: 1024 MB
  Max retries: 10
  Retry delay: 2 seconds

Using decompressor: xzcat
Opening block device for writing: /dev/mmcblk1
Starting download from: https://example.com/path/to/image.raw.xz
Content length: 547832416 bytes

Download: 27.92 MB / 522.45 MB (5.3%) | 27.92 MB/s | Decompressed: [░░░░░░░░░░] 0.4% | Written: 63.00 MB | 62.99 MB/s
Download: 101.40 MB / 522.45 MB (19.4%) | 33.78 MB/s | Decompressed: [░░░░░░░░░░] 5.3% | Written: 63.00 MB | 20.99 MB/s
...
Download: 506.08 MB / 522.45 MB (96.9%) | 31.60 MB/s | Decompressed: [█░░░░░░░░░] 12.8% | Written: 319.00 MB | 19.92 MB/s
Download: Done | Decompressed: [██████████████████░░] 91.5% | Written: 1407.00 MB | 18.57 MB/s
...
Download: Done | Decompressed: Done | Written: Done

Download complete: 522.45 MB in 16.46s (31.75 MB/s)
Decompression complete: 5120.00 MB in 87.83s (58.29 MB/s)
Write complete: 5120.00 MB in 281.23s (18.21 MB/s)
Compression ratio: 9.80x

Command Options

fls from-url

Flash an image from a URL to a block device.

fls from-url [OPTIONS] <URL> <DEVICE>

Arguments:

• <URL> - URL to download the image from
• <DEVICE> - Destination device path (e.g., /dev/sdb, /dev/mmcblk1)

Options:

• -k, --insecure-tls - Ignore SSL certificate verification
• --cacert <CACERT> - Path to CA certificate PEM file for TLS validation
• --buffer-size <SIZE> - Buffer size in MB for download buffering (default: 1024)
• --max-retries <NUM> - Maximum number of retry attempts (default: 10)
• --retry-delay <SECONDS> - Delay in seconds between retry attempts (default: 2)
• --debug - Enable debug output
• --o-direct - Enable O_DIRECT mode for direct I/O (bypasses OS cache)
• -H, --header <HEADER> - Custom HTTP headers (can be used multiple times, format: Header: value)
• -i, --progress-interval <SECONDS> - Progress update interval in seconds (default: 0.5, accepts float values)
• -n, --newline-progress - Print progress on new lines instead of overwriting

Safety Notes

⚠️ WARNING: fls writes directly to block devices and will overwrite all data on the target device. Always double-check the device path before running.

• Requires root/sudo privileges to write to block devices
• Ensure the target device is not mounted
• Verify the device path to avoid data loss
• Use lsblk or fdisk -l to identify the correct device before flashing