How to Fix Linux Segmentation Fault (core dumped) Error

In this tutorial, you'll learn about How to Fix Linux Segmentation Fault (core dumped) Error. We cover key concepts, practical examples, and best practices.

You run a program and get Segmentation fault (core dumped) — the program tried to access memory it does not have permission to access, often due to a bug, corrupted binary, or hardware issue.

The Problem

./myapp
Segmentation fault (core dumped)

Step-by-Step Fix

Step 1: Enable core dumps

ulimit -c unlimited

Make permanent in ~/.bashrc:

echo 'ulimit -c unlimited' >> ~/.bashrc

Step 2: Reproduce the crash

./myapp

Check for the core file:

ls -la core* /var/lib/systemd/coredump/

Step 3: Analyze with gdb

gdb ./myapp core

Inside gdb, get a backtrace:

(gdb) bt
(gdb) bt full

This shows the exact function call chain that led to the crash.

Step 4: Check for common causes

Buffer overflow:

char buf[10];
strcpy(buf, "this string is way too long");  // WRONG
strncpy(buf, "short", sizeof(buf) - 1);       // RIGHT

Null pointer dereference:

int *p = NULL;
*p = 42;  // WRONG

Use-after-free:

free(ptr);
ptr[0] = 0;  // WRONG

Step 5: Reinstall the affected package

sudo apt reinstall <package>

Step 6: Check for hardware issues

Run memory test:

sudo apt install memtester
memtester 1024 1

Check system logs:

dmesg | grep -i "segfault\|error"

Expected:

[12345.678] myapp[1234]: segfault at 7f1234 ip 00007f5678 sp 00007f9012 error 6

Step 7: Update system and libraries

sudo apt update && sudo apt upgrade

Prevention Tips

• Enable core dumps in development environments
• Use AddressSanitizer during development: gcc -fsanitize=address -g
• Always check pointer validity before dereferencing
• Use valgrind to detect memory errors
• Keep software updated to get bug fixes

Common Mistakes with segfault

1. Non-exhaustive pattern matches that compile with warnings then crash at runtime
2. Misunderstanding that String is [Char] with poor performance for large text operations
3. Using foldl instead of foldl' causing stack overflow on large lists

These mistakes appear frequently in real-world LINUX code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

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