Backup Manager

Automatic folder backup with real-time updates, written in low-level C.

Overview

Backup Manager is a low-level Linux backup system written in pure C.
It provides real-time directory mirroring using filesystem event monitoring, process isolation, and iterative directory traversal.

The project focuses on correctness, robustness, and system-level mechanisms, rather than high-level abstractions.

Key Features

Feature	Description
✅ Real-time backup	Automatically synchronizes changes using Linux inotify
✅ Full directory mirroring	Source and target directories are kept structurally identical
✅ Iterative traversal	All subdirectories are processed without recursive function calls
✅ Process isolation	Each backup runs in its own child process
✅ Signal handling	Clean shutdown using POSIX signals
✅ Safe symlink handling	Symbolic links are preserved and rewritten correctly
✅ Robust memory management	Explicit allocation control with clear ownership and cleanup
✅ POSIX-compliant	Uses standard UNIX system calls only

How It Works

1. The main process starts an interactive CLI.
2. When add is called, the program forks a child process for the backup task.
3. The child process:
   • Performs an initial full synchronization (sync_mirror)
   • Registers all directories with inotify
   • Waits for filesystem events
4. On any detected event, a safe full resynchronization is performed.
5. The parent process tracks active backups and controls them via signals.

Architecture Overview

• sop-backup.c — main program, CLI, signal handling
• kopia_operacje.c — backup lifecycle operations (add, end, restore)
• proces_potomny.c — child worker logic and inotify handling
• zarzadzanie.c — directory mirroring and cleanup logic
• pomocnicze.c — utilities (paths, parsing, filesystem helpers)

Directory Synchronization Strategy

Instead of applying incremental diffs, the system:

• Iteratively traverses the entire source tree
• Copies only files that are newer or missing
• Removes files from the target that no longer exist in the source

This approach is:

• Safer against missed inotify events
• Easier to reason about correctness
• Efficient enough for typical user directories

Command-Line Interface

add <source> <target1> [target2 ...]
end <source> <target>
list
restore <source> <backup>
exit

Example

add "/home/user/Documents" "/mnt/backup/Documents"

Technologies Used

• C (GNU11)
• POSIX system calls
• fork, waitpid, signals
• inotify
• opendir, readdir, lstat
• Manual memory management

Project Goals

• Demonstrate low-level filesystem programming
• Practice safe process management
• Implement real-time synchronization without external libraries
• Ensure deterministic and debuggable behavior

License

MIT License