Sync

One-way file synchronization tool written in Go. Supports local and remote (SFTP) directories.

Installation

From source

go build -o sync ./cmd/sync

Using Make

make build

Using Docker

docker build -t sync:latest .

Usage

./sync [options] <source> <target>

Arguments

• <source> - Source directory path or [user@]host:/path for remote (required)
• <target> - Target directory path or [user@]host:/path for remote (required)

Options

• -d, --delete-missing - Delete files in target that don't exist in source
• -c, --checksum - Compare files using SHA256 checksum (slower but more accurate)
• -i, --identity FILE - Path to SSH private key (default: ~/.ssh/id_ed25519, ~/.ssh/id_rsa)
• -p, --port PORT - SSH port (default: 22)
• --password PASS - SSH password (prefer key-based auth)
• -h, --help - Show help message

Examples

Local to local

# Basic synchronization
./sync /path/to/source /path/to/target

# Delete files in target that don't exist in source
./sync -d /path/to/source /path/to/target

# Use SHA256 checksum for comparison (more accurate)
./sync -c /path/to/source /path/to/target

# Combine flags
./sync -d -c /path/to/source /path/to/target

Local to remote (SFTP)

# Push local files to remote server
./sync /local/path user@host:/remote/path

# With custom SSH key and port
./sync -i ~/.ssh/my_key -p 2222 /local/path user@host:/remote/path

Remote to local (SFTP)

# Pull remote files to local directory
./sync user@host:/remote/path /local/path

Remote to remote (SFTP)

# Sync between two remote servers
./sync user@host1:/path user@host2:/path

Docker

# Run with mounted volumes
docker run --rm \
  -v /path/to/source:/source:ro \
  -v /path/to/target:/target \
  sync:latest /source /target

# With delete-missing flag
docker run --rm \
  -v /path/to/source:/source:ro \
  -v /path/to/target:/target \
  sync:latest -d /source /target

How it works

1. Scans the source directory recursively
2. For each file in source:
   • If file doesn't exist in target → copy
   • If file exists → compare (by size/modtime or SHA256 checksum) → update if different
3. If --delete-missing is enabled:
   • Scans target directory
   • Deletes files that don't exist in source

File comparison methods

• Default (metadata): Compares file size and modification time. Fast but may miss files with same size/time but different content.
• Checksum (-c): Compares SHA256 hash of file contents. Slower but guarantees detection of any content difference.

SSH authentication

When using remote paths ([user@]host:/path), the tool connects via SFTP over SSH. Authentication methods are tried in this order:

1. Password — if provided via --password flag
2. SSH agent — if SSH_AUTH_SOCK is set
3. Private key — from --identity flag, or defaults: ~/.ssh/id_ed25519, ~/.ssh/id_rsa

Host key verification uses ~/.ssh/known_hosts when available.

Building

Make commands

make build        # Build binary for current platform
make test         # Run tests
make clean        # Remove build artifacts
make build-docker # Build Docker image
make build-all    # Build multi-platform Docker images (requires buildx)
make dist         # Build binaries for all platforms

Multi-platform builds

Build binaries for all supported platforms:

make dist

This creates binaries in dist/ directory:

• sync-linux-amd64
• sync-linux-arm64
• sync-darwin-amd64
• sync-darwin-arm64
• sync-windows-amd64.exe

Docker multi-platform

Build Docker images for multiple platforms using buildx:

make build-all

Supported platforms:

• linux/amd64
• linux/arm64
• darwin/amd64
• darwin/arm64
• windows/amd64

Testing

go test ./...
# or
make test