Linux System-Wide File Descriptor (FD) Table Monitor

📌 Overview

This C-based Linux utility explores how the operating system tracks open files. It extracts and displays various views of file descriptor data using the /proc virtual filesystem. Users can generate per-process, system-wide, vnode-based, and composite FD tables, save them to text or binary files, and evaluate performance based on output format.

👤 Author

Abd-Ur-Rehman

🎯 Features

• View per-process FD tables
• Generate system-wide FD tables with filenames
• Display vnode-based tables using inode numbers
• Combine all views into a composite table
• Show summary of FD counts per process
• Highlight processes exceeding the FD threshold
• Save the composite table to:
  • Plain text file
  • Binary file with custom serialization
• Performance comparison between output formats

🧠 Approach

• Command-line interface to select views and output options
• Reads from /proc/[pid]/fd to extract FD metadata
• Uses:
  • readlink() for filename resolution
  • stat() for inode retrieval
  • opendir() and readdir() for directory traversal
• Modular function design for each table and file type
• Composite view combines PID, FD, filename, and inode data
• Output can be redirected to the screen, a text file, or a binary file

🛠️ Compilation Instructions

Run on a Linux system using:

gcc -Wall -Wextra -std=c99 -Werror -g -o FD_tables FD_tables.c

🚩 Supported Command-Line Arguments

🔹 Flagged Arguments

• --per-process: Show only the process FD table.
• --systemWide: Show only the system-wide FD table.
• --Vnodes: Show only the Vnodes FD table.
• --composite: Show only the composed FD table.
• --summary: Show a summary of the number of FDs open per process.
• --threshold=X: Show only processes with more than X FDs open.

📋 Command-Line Usage Examples

Command	Description
./FD_tables	Displays the composite table by default
./FD_tables 1234 --per-process	Shows FD table for PID 1234
./FD_tables --systemWide	Displays system-wide FD table
./FD_tables --threshold=2	Lists processes with >2 FDs
./FD_tables --output_TXT	Saves composite table to compositeTable.txt
./FD_tables 1234 --output_binary	Saves PID 1234’s composite table to compositeTable.bin

🧪 Testing

Tested various combinations of command-line arguments, including:

• Valid/invalid PIDS
• All flags together
• File-saving with invalid file paths
• Thresholds <= 0 and > 0

📊 Performance Evaluation (Bonus)

Case	Avg Time (s)	Text Size (bytes)	Binary Size (bytes)
All Processes	0.023	11262	9238
Single PID	0.0166	2122.8	1595.8

Observations

• Binary output saves more space than text
• Processing time is dependent on data size, not output format
• Output is consistent and reliable

⚠️ Disclaimers

• Table formats follow Prof. Marcelo’s demo specifications
• Tables for specific PIDS exclude row indices
• Composite and threshold tables maintain consistent output order
• #define _GNU_SOURCE is used to access DT_LNK and DT_DIR

📚 References

• snprintf - GeeksforGeeks
• define _GNU_SOURCE - StackOverflow
• PATH_MAX in Linux - StackOverflow
• Standard Deviation Calculator