Command documentation sourced from the linux-command project This comprehensive command reference is part of the linux-command documentation project.

catchsegv - Catch Segmentation Faults

The catchsegv command is a GNU glibc utility that helps debug segmentation faults by creating stack traces when programs crash due to memory access violations. It works by preloading a special library that intercepts segmentation fault signals and generates useful debugging information including memory maps and stack traces. This tool is particularly useful for developers who need to diagnose why their programs are crashing due to invalid memory access, null pointer dereferences, or buffer overflows.

Basic Syntax

catchsegv [OPTIONS] PROGRAM [ARGUMENTS...]

How It Works

catchsegv works by:

1. Preloading the libSegFault.so library using LD_PRELOAD
2. Intercepting SIGSEGV (segmentation fault) signals
3. Generating a stack trace and memory map when the fault occurs
4. Displaying diagnostic information to help identify the crash location

Common Usage Patterns

Basic Usage

catchsegv ./my_program
catchsegv ./buggy_app argument1 argument2

With Environment Variables

catchsegv env VAR=value ./my_program

With Options

catchsegv -- ./program_with_dash_args

Usage Examples

Basic Debugging

Simple Program Crash

# Debug a crashing program
catchsegv ./my_program

# Debug with arguments
catchsegv ./server --port 8080 --debug

# Debug with environment variables
catchsegv env LD_LIBRARY_PATH=/usr/local/lib ./my_app

Common Crash Scenarios

# Debug segmentation fault in compiled program
catchsegv ./a.out

# Debug with input file
catchsegv ./parser input.txt

# Debug interactive program
catchsegv ./interactive_tool

Development Workflow

During Development

# Compile with debug symbols (recommended)
gcc -g -o myprogram myprogram.c

# Run with catchsegv for debugging
catchsegv ./myprogram

# Combine with valgrind for comprehensive analysis
valgrind --tool=memcheck ./myprogram

Testing and Quality Assurance

# Test program with various inputs
for input in test_*.txt; do
    echo "Testing with $input:"
    catchsegv ./parser "$input"
    echo "---"
done

# Stress test with catchsegv
catchsegv ./stress_test --iterations 10000

Integration with Build Systems

Makefile Integration

debug: myprogram
	catchsegv ./myprogram

test: myprogram
	for test in tests/*.in; do \
		catchsegv ./myprogram $$test; \
	done

Shell Script Testing

#!/bin/bash
# Automated testing with crash detection

PROGRAM="./my_program"
TEST_DIR="test_cases"

for test_file in "$TEST_DIR"/*.txt; do
    echo "Testing: $test_file"
    if catchsegv "$PROGRAM" "$test_file"; then
        echo "✓ Test passed: $test_file"
    else
        echo "✗ Test failed: $test_file"
        # Continue with other tests
    fi
done

Advanced Usage

Combined Debugging

With GDB

# First use catchsegv to identify crash location
catchsegv ./my_program

# Then use GDB for detailed analysis
gdb ./my_program
(gdb) run
(gdb) bt  # Backtrace when it crashes

With Strace

# System calls analysis with crash detection
catchsegv strace -o trace.log ./my_program

# Filter specific system calls
catchsegv strace -e trace=open,read,write ./my_program

With Ltrace

# Library calls analysis
catchsegv ltrace -o ltrace.log ./my_program

# Follow fork processes
catchsegv ltrace -f ./my_program

Memory Analysis

Combined with Memory Checkers

# Run with both catchsegv and valgrind
catchsegv valgrind --leak-check=full ./my_program

# Use with AddressSanitizer (GCC/Clang)
gcc -fsanitize=address -g -o myprogram myprogram.c
catchsegv ./myprogram

Buffer Overflow Detection

# Test with intentionally large inputs
catchsegv ./buffer_test "$(python -c 'print "A" * 10000)')"

# Test with edge cases
catchsegv ./parser "$(echo -e '\x00\x01\x02\x03')"

Troubleshooting Common Issues

Compilation Problems

Missing Debug Symbols

# Always compile with debug symbols
gcc -g -O0 -o myprogram myprogram.c

# Check if binary has debug symbols
file myprogram
objdump -h myprogram | grep debug

Optimization Issues

# Debug with optimization disabled
gcc -g -O0 -Wall -Wextra -o debug_version myprogram.c
catchsegv ./debug_version

# Debug with different optimization levels
gcc -g -O1 -o test_o1 myprogram.c
catchsegv ./test_o1

Runtime Issues

Library Path Problems

# Set library path explicitly
catchsegv env LD_LIBRARY_PATH=/usr/local/lib ./my_program

# Check required libraries
ldd ./my_program

# Run with library path debugging
catchsegv env LD_DEBUG=libs ./my_program

Permission Issues

# Check executable permissions
ls -la ./my_program

# Make executable if needed
chmod +x ./my_program

# Run with proper permissions
catchsegv sudo -u user ./my_program

Interpretation Issues

Reading Stack Traces

# Use addr2line to get source line from addresses
addr2line -e ./my_program 0x400512

# Get more detailed symbol information
nm -C ./my_program

# Demangle C++ symbols
c++filt _Z1fi

Core File Analysis

# Enable core dumps
ulimit -c unlimited

# Analyze core dump with GDB
gdb ./my_program core
(gdb) bt full
(gdb) info registers

Practical Examples

Real-World Debugging Scenarios

Null Pointer Dereference

// null_pointer.c
#include <stdio.h>

int main() {
    int *ptr = NULL;
    *ptr = 42;  // This will cause segfault
    return 0;
}

# Compile and debug
gcc -g -o null_pointer null_pointer.c
catchsegv ./null_pointer

Buffer Overflow

// buffer_overflow.c
#include <string.h>

int main() {
    char buffer[10];
    strcpy(buffer, "This is a very long string that will overflow");
    return 0;
}

# Compile and debug
gcc -g -fno-stack-protector -o buffer_overflow buffer_overflow.c
catchsegv ./buffer_overflow

Double Free

// double_free.c
#include <stdlib.h>

int main() {
    int *ptr = malloc(sizeof(int));
    free(ptr);
    free(ptr);  // Double free - causes segfault
    return 0;
}

# Compile and debug
gcc -g -o double_free double_free.c
catchsegv ./double_free

Automated Testing Integration

CI/CD Pipeline

# GitHub Actions example
- name: Run tests with crash detection
  run: |
    for test in tests/*; do
      if ! catchsegv ./my_program "$test"; then
        echo "Test $test failed with segmentation fault"
        exit 1
      fi
    done

Regression Testing

#!/bin/bash
# regression_test.sh

FAILED_TESTS=0

for test_case in test_cases/*.input; do
    echo "Running test: $test_case"
    if catchsegv timeout 30s ./my_program < "$test_case" > "output_$(basename $test_case)"; then
        echo "✓ $test_case passed"
    else
        echo "✗ $test_case failed"
        ((FAILED_TESTS++))
    fi
done

if [ $FAILED_TESTS -gt 0 ]; then
    echo "$FAILED_TESTS tests failed"
    exit 1
fi

Integration with Development Tools

IDE Integration

VS Code Tasks

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "Debug with catchsegv",
            "type": "shell",
            "command": "catchsegv",
            "args": ["${workspaceFolder}/build/myprogram"],
            "group": "build",
            "presentation": {
                "echo": true,
                "reveal": "always",
                "focus": false,
                "panel": "shared"
            }
        }
    ]
}

Makefile Target

.PHONY: debug-catchsegv
debug-catchsegv: $(TARGET)
	@echo "Running with catchsegv..."
	catchsegv ./$(TARGET)

.PHONY: test-all
test-all: $(TARGET)
	@for test in tests/*.txt; do \
		echo "Testing $$test:"; \
		catchsegv ./$(TARGET) $$test; \
		echo "---"; \
	done

Container Development

Dockerfile

FROM ubuntu:latest

RUN apt-get update && apt-get install -y \
    build-essential \
    libc6-dbg \
    gdb \
    && rm -rf /var/lib/apt/lists/*

WORKDIR /app
COPY . .

# Build with debug symbols
RUN gcc -g -o myprogram myprogram.c

# Debug command
CMD ["catchsegv", "./myprogram"]

Docker Compose

version: '3.8'
services:
  debug:
    build: .
    command: catchsegv ./my_program --debug
    volumes:
      - .:/app
      - core_dumps:/tmp/core_dumps
    environment:
      - LD_LIBRARY_PATH=/usr/local/lib

Performance Considerations

Overhead Analysis

Runtime Performance

# Benchmark with and without catchsegv
time ./my_program
time catchsegv ./my_program

# Measure memory usage
/usr/bin/time -v ./my_program
/usr/bin/time -v catchsegv ./my_program

Optimization Impact

# Test different optimization levels
for opt_level in O0 O1 O2 O3; do
    echo "Testing with -$opt_level:"
    gcc -g -$opt_level -o test_$opt_level myprogram.c
    time catchsegv ./test_$opt_level
    echo "---"
done

Security Considerations

Safe Usage

Production Environments

# Use only in development/testing
if [ "$ENVIRONMENT" = "development" ]; then
    catchsegv ./my_program
else
    ./my_program
fi

# Log crashes instead of interactive debugging
catchsegv ./my_program 2>&1 | tee crash_log.txt

Core Dump Management

# Control core dump generation
ulimit -c unlimited  # Enable core dumps
ulimit -c 0          # Disable core dumps

# Set core dump pattern
echo '/tmp/core_%e.%p.%h.%t' > /proc/sys/kernel/core_pattern

Limitations and Alternatives

When to Use Other Tools

Use GDB when:

• Need interactive debugging
• Want to examine program state
• Need to set breakpoints
• Require step-by-step execution

Use Valgrind when:

• Need memory leak detection
• Want detailed memory analysis
• Need to profile memory usage
• Detect uninitialized memory access

Use AddressSanitizer when:

• Need compile-time detection
• Want better performance than valgrind
• Need stack trace information
• Detect buffer overflows

Use Core Dumps when:

• Need post-mortem analysis
• Want to analyze crashes in production
• Need to preserve crash state
• Analyze crashes on different machines

Best Practices

1. Always compile with debug symbols (-g flag) when using catchsegv
2. Use catchsegv during development and testing to catch crashes early
3. Combine with other tools like GDB for comprehensive debugging
4. Log output to files for later analysis in automated environments
5. Test with various inputs to identify edge cases that cause crashes
6. Use proper build configurations with optimization flags disabled for debugging
7. Monitor system resources when debugging large applications
8. Document crash scenarios for future reference and regression testing
9. Integrate into CI/CD pipelines to catch crashes before deployment
10. Use environment controls to enable/disable debugging in production

Performance Tips

1. Disable optimization (-O0) for accurate debugging information
2. Use debug builds with additional safety checks
3. Limit input size during initial debugging to reduce noise
4. Use timeout mechanisms for potentially infinite loops
5. Monitor system load when debugging resource-intensive applications
6. Combine with profilers to identify performance bottlenecks
7. Use parallel testing to speed up debugging multiple test cases
8. Log systematically to track down intermittent crashes

The catchsegv command is an essential tool for Linux developers dealing with segmentation faults. While it provides basic crash detection and stack tracing, it serves as an excellent first step in the debugging process before moving to more sophisticated tools like GDB or Valgrind. Its simplicity and integration with the GNU toolchain make it invaluable for rapid crash identification during development and testing phases.