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Network Connectivity Checker (netcheck)

A powerful, feature-rich command-line tool for testing network connectivity to multiple hosts and ports with parallel processing, multiple output formats, and automatic dependency management.

Features

Core Testing Features

  • ✅ ICMP Ping Testing - Test connectivity with ping (accepts URLs and IPs)
  • ✅ DNS Lookup - Resolve hostnames to IPs with multiple fallback methods (accepts URLs)
  • ✅ TCP Port Testing - Check if ports are open and responsive
  • ✅ HTTP Status Checking - Get HTTP/HTTPS response codes and performance metrics
  • ✅ SSL Certificate Validation - Check certificate expiry and validity

Network Diagnostics (v1.2.0)

  • 🆕 Show Network Interfaces - Display all network interfaces with IPs (--my-ip)
  • 🆕 Retry Logic - Automatically retry failed connections with configurable count and delay
  • 🆕 HTTP Status Codes - Check website status with response time and size (-s/--status)
  • 🆕 SSL Certificate Check - Validate SSL/TLS certificates with expiry warnings (--cert)

Performance & Automation

  • ✅ Parallel Processing - Check multiple hosts simultaneously (up to 256 jobs)
  • ✅ Quick Mode Parallel Processing - Automatic parallel execution for wide IP ranges (>5 tests)
  • ✅ Quick Mode Output File - Save quick mode results with -o/--output flag
  • ✅ Response Time Measurement - See connection latency in milliseconds

Input & Output

  • ✅ Multiple Output Formats - Text, JSON, CSV, XML
  • ✅ Quick Test Mode - Test single host without creating files
  • ✅ IP Range Support - Check IP ranges (192.168.1.1-50) and CIDR (10.0.0.0/24)
  • ✅ Port Ranges - Check port ranges (8000-8100) or multiple ports (80,443,8080)
  • ✅ CSV File Support - Read from CSV files (host,port format)
  • ✅ Dated Result Files - Automatic timestamped output files

Quality & Usability

  • ✅ Progress Bar - Real-time progress tracking
  • ✅ Version Information - Check tool version with -v flag
  • ✅ Input Validation - Comprehensive validation with helpful warnings for malformed input
  • ✅ Automatic Dependency Installation - Installs telnet and netcat if missing
  • ✅ Flexible Input - File, stdin, or quick test mode
  • ✅ Man Page & Tab Completion - Full documentation and bash completion
  • ✅ Multi-OS Support - Ubuntu, Debian, CentOS, Fedora, Arch, openSUSE

Installation

Option 1: From Snap Store (Recommended - Works on ALL Linux!)

sudo snap install netcheck

Enable network diagnostics (required for -p and --my-ip flags):

sudo snap connect netcheck:network-observe

Benefits: Auto-updates, universal Linux support, sandboxed security

Note: The network-observe connection is required for:

  • ICMP ping tests (-p/--ping flag)
  • Network interface information (--my-ip flag)

Without this connection, these features will fail with permission errors. All other features (TCP port tests, DNS lookup, HTTP status, SSL cert checks, retry logic) work without this connection.

Option 2: DEB Package (Ubuntu/Debian)

# Build the package
./build-deb.sh

# Install
sudo dpkg -i netcheck_1.2.0.deb

Option 3: Manual System-wide Installation

# Using Makefile (recommended)
sudo make install

# Or directly
sudo ./install.sh

This will:

  • Install the command as netcheck in /usr/local/bin
  • Automatically detect your OS and install dependencies (telnet, netcat)
  • Create a man page (man netcheck)
  • Add bash tab completion
  • Works on: Ubuntu, Debian, CentOS, RHEL, Fedora, Arch, openSUSE

Option 4: Local Installation (No sudo)

chmod +x check_ip.sh
# Run directly: ./check_ip.sh

See: PUBLISHING_GUIDE.md for package publishing details

Quick Start

Quick Test (Single Host)

# Test a single host - no files created, instant results
netcheck -q google.com 443
netcheck -q 192.168.1.1 80
netcheck -q localhost 3306

# Test multiple ports at once
netcheck -q server.com 80,443,8080
netcheck -q localhost 80,443

# Test port range
netcheck -q localhost 8000-8100
netcheck -q server.com 9000-9010

# NEW: Test IP range (multiple hosts)
netcheck -q 10.90.95.72-75 50000
netcheck -q 192.168.1.1-10 22

DNS Lookup

# Resolve hostname to IP addresses
netcheck -d google.com
netcheck -d github.com

# NEW: Also accepts URLs (strips scheme/path automatically)
netcheck -d https://api.example.com
netcheck -d http://services.company.com:8080/path

ICMP Ping Test

# Ping a host (4 packets with statistics)
netcheck -p 8.8.8.8
netcheck -p google.com

# NEW: Also accepts URLs (strips scheme/path automatically)
netcheck -p https://github.com
netcheck -p http://api.example.com

Network Interface Information (v1.2.0)

# Show active network interfaces only (default)
netcheck --my-ip
netcheck -ip

# Show all interfaces including inactive ones
netcheck --my-ip --all

Output:

Network Interface Information
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

📡 Active Network Interfaces (UP only):
   Use '--my-ip --all' to show all interfaces

Interface: enp1s0
  IPv4: 10.90.19.195
  Status: ✅ UP

Interface: wlp0s20f3
  IPv4: 192.168.0.137
  Status: ✅ UP

🌐 Default Gateway: 192.168.0.1
   Via Interface: wlp0s20f3

🌍 Public IP Address:
  154.91.162.123

HTTP Status Checking (v1.2.0)

# Check HTTP/HTTPS status codes
netcheck -s https://google.com
netcheck -s http://api.example.com

# Get detailed headers with verbose mode
netcheck -s https://github.com -V

Output:

HTTP Status Check for: https://google.com
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Sending HTTP request...

┌─────────────────────────────────────────────┐
│ URL: https://google.com                     │
├─────────────────────────────────────────────┤
│ Status: ✅ SUCCESS                          │
│ Code: 200 OK                                │
│ Response Time: 145ms                        │
│ Content Size: 15.2 KB                       │
└─────────────────────────────────────────────┘

SSL Certificate Validation (v1.2.0)

# Check SSL/TLS certificate
netcheck --cert https://google.com
netcheck --cert github.com:443

# Verbose mode shows SANs (Subject Alternative Names)
netcheck --cert google.com -V

Output:

SSL/TLS Certificate Check for: google.com:443
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Connecting to google.com:443...

┌─────────────────────────────────────────────┐
│ Host: google.com:443                        │
├─────────────────────────────────────────────┤
│ Status: ✅ VALID                            │
├─────────────────────────────────────────────┤
│ Certificate Details:                        │
├─────────────────────────────────────────────┤
│ Subject: CN = *.google.com                  │
│ Issuer: C = US, O = Google Trust Servi...  │
├─────────────────────────────────────────────┤
│ Valid From: Oct 15 08:15:42 2024 GMT       │
│ Valid Until: Jan  7 08:15:41 2025 GMT      │
│ Days Until Expiry: 62                       │
└─────────────────────────────────────────────┘

Retry Failed Connections (v1.2.0)

# Retry failed connections 3 times (works with all modes)
netcheck --retry 3 hosts.txt

# Custom retry delay (default: 1 second)
netcheck --retry 3 --retry-delay 2 hosts.txt

# Works in quick mode too
netcheck -q 192.168.1.1 80 --retry 5 --retry-delay 1

Version Information

# Check netcheck version
netcheck -v
netcheck --version

Output:

DNS Lookup for: google.com
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Hostname: google.com

IP Addresses:
  142.250.202.78
  2a00:1450:4019:812::200e (IPv6)

Aliases:

Reverse DNS:
  pnfjra-an-in-f14.1e100.net.
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Version Information

# Check netcheck version
netcheck -v
netcheck --version

Output:

Quick Test Mode
Host: localhost
Port(s): 80,443
Timeout: 5s

Testing 2 port(s)...

┌─────────────────────────────────────────────┐
│ Host: localhost                             │
│ Port: 80                                    │
├─────────────────────────────────────────────┤
│ Status: ✓ CONNECTED                         │
│ Method: netcat                              │
│ Response Time: 1ms                          │
└─────────────────────────────────────────────┘

Quick Test Summary
════════════════════════════════════════════
Total Ports: 2
Successful:  1
Failed:      1
════════════════════════════════════════════

CSV File Support

# Read from CSV file
netcheck --csv hosts.csv

# CSV from stdin
cat hosts.csv | netcheck --csv

# Piped CSV data
echo -e "host,port\ngoogle.com,443\nlocalhost,80" | netcheck --csv

CSV Format:

host,port
google.com,443
server.local,80
192.168.1.1,22
192.168.1.1-5,80
localhost,"80,443,8080"
10.0.0.0/24,22

Features:

  • Automatic header detection and skipping
  • Supports quoted fields for multiple ports
  • Supports IP ranges in CSV: 192.168.1.1-50,80
  • Supports CIDR notation: 192.168.1.0/24,22
  • Supports multiple ports: host,"80,443,8080"

Batch Testing

Create a file hosts.txt:

google.com 443
github.com 443
192.168.1.1 80
localhost 3306
8.8.8.8 53

Run the check:

netcheck hosts.txt

Usage

netcheck [OPTIONS] [input_file]

OPTIONS:
    -t, --timeout <seconds>     Connection timeout (default: 5)
    -j, --jobs <number>         Max parallel jobs (default: 10)
    -V, --verbose               Verbose output
    -f, --format <format>       Output format: text, json, csv, xml (default: text)
    -c, --combined              Create combined report with all results
    -q, --quick <host> <port>   Quick test mode (no files created)
    -o, --output <file>         Save quick mode results to file
    -d, --dns <hostname>        Resolve DNS and show IP address (accepts URLs)
    -p, --ping <host>           Ping host using ICMP (accepts URLs/IPs)
    -s, --status <url>          Check HTTP/HTTPS status code and response time
    --cert <host>               Check SSL/TLS certificate validity and expiration
    --my-ip, -ip                Show all network interfaces and IP addresses (UP only)
    --my-ip --all               Show all interfaces including inactive ones
    --retry <number>            Retry failed connections N times (default: 1, no retry)
    --retry-delay <seconds>     Delay between retries in seconds (default: 1)
    --csv                       Input file is in CSV format (host,port)
    -v, --version               Show version information
    -h, --help                  Show help message

Examples

Basic Usage

# Check hosts from file
netcheck hosts.txt

# From stdin
cat hosts.txt | netcheck

# Verbose mode
netcheck -V hosts.txt
echo "google.com 443" | netcheck -V

DNS Resolution

# Lookup hostname
netcheck -d google.com
netcheck -d github.com

# Works with URLs too (strips http://, https://, paths)
netcheck -d https://api.example.com
netcheck -d http://services.company.com:8080/api/v1

ICMP Ping

# Ping IP address
netcheck -p 8.8.8.8
netcheck -p 192.168.1.1

# Ping hostname
netcheck -p google.com

# Works with URLs too
netcheck -p https://github.com

netcheck -d google.com netcheck -d github.com

Shows: IPv4, IPv6, aliases, reverse DNS


### Version Check
```bash
# Show netcheck version
netcheck -v
netcheck --version

Fast Parallel Checking

# Check 20 hosts simultaneously with 2-second timeout
netcheck -t 2 -j 20 hosts.txt

# High-speed scanning with 100 parallel jobs
netcheck -j 100 -t 1 large-list.txt

Different Output Formats

JSON Output:

netcheck -f json hosts.txt

Output: result.txt

{"check_date":"2025-11-11 10:59:21","results":[
  {"status":"success","host":"google.com","port":443,"method":"netcat","timestamp":"2025-11-11 10:59:21"}
]}

CSV Output:

netcheck -f csv hosts.txt

Output: result.txt

Status,Host,Port,Method,Timestamp
"SUCCESS","google.com",443,"netcat","2025-11-11 11:00:05"

XML Output:

netcheck -f xml hosts.txt

Combined Report

# Get all results (success + failures) in one file
netcheck -c hosts.txt
# Creates: combined-2025-11-11.txt

Verbose Mode

# See detailed output for each host
netcheck -v hosts.txt

Input Format

Each line should contain: HOST PORT(S)

# Basic format
192.168.1.1 80

# Multiple ports (comma-separated)
192.168.1.1 80,443,8080

# Port range
192.168.1.1 8000-8100

# IP range (last octet)
192.168.1.1-50 80

# CIDR notation (subnet)
192.168.1.0/24 80

# Combined: IP range + multiple ports
192.168.1.1-10 80,443,8080

# Comments are supported
# This is a comment
google.com 443

Range Examples

IP Ranges:

  • 192.168.1.1-50 80 - Checks 192.168.1.1 through 192.168.1.50 on port 80 (50 checks)
  • 10.0.0.1-5 443 - Checks 5 IPs on port 443

CIDR Notation:

  • 192.168.1.0/24 80 - Checks entire /24 subnet (254 hosts)
  • 10.0.0.0/28 22 - Checks /28 subnet (14 usable hosts)
  • Note: Network and broadcast addresses are skipped for /24 and smaller

Multiple Ports:

  • server.com 80,443,8080 - Checks 3 ports on same host
  • 192.168.1.1 22,80,443,3306,8080 - Checks 5 ports

Port Ranges:

  • localhost 8000-8100 - Checks ports 8000 through 8100 (101 ports)
  • server.com 9000-9010 - Checks 11 ports
  • Note: Port ranges >1000 ports are limited to first 1000

Combined:

  • 192.168.1.1-10 80,443 - 10 IPs × 2 ports = 20 checks
  • 10.0.0.0/28 22,80,443 - 14 IPs × 3 ports = 42 checks

Output Files

  • result.txt - Successful connections
  • fail-YYYY-MM-DD.txt - Failed connections (dated)
  • combined-YYYY-MM-DD.txt - All results (when using -c flag)

Use in Scripts

#!/bin/bash

# Check if database is up
if netcheck -q db.example.com 3306 > /dev/null 2>&1; then
    echo "Database is online!"
else
    echo "Database is down!"
    exit 1
fi

# Batch check and parse JSON
netcheck -f json servers.txt
# Process result.txt with jq or other JSON tools

Requirements

  • Bash 4.0+
  • telnet (auto-installed)
  • netcat (auto-installed)
  • timeout command (usually pre-installed)

Troubleshooting

Dependencies Not Installing Automatically

If automatic installation fails, install manually:

Ubuntu/Debian:

sudo apt install telnet netcat-openbsd

CentOS/RHEL/Fedora:

sudo yum install telnet nc
# or
sudo dnf install telnet nc

Arch/Manjaro:

sudo pacman -S inetutils openbsd-netcat

Permission Denied

Make sure the script is executable:

chmod +x check_ip.sh

For system-wide installation, use sudo:

sudo ./install.sh

Uninstallation

sudo ./uninstall.sh

This removes:

  • /usr/local/bin/netcheck
  • Man page
  • Bash completion

Dependencies (telnet, netcat) are NOT removed.

Documentation

View full manual:

man netcheck

Advanced Examples

Scan Entire Subnet

# Check SSH on entire /24 subnet
echo "192.168.1.0/24 22" | netcheck -j 50

# Check common web ports on subnet
echo "10.0.0.0/26 80,443,8080" | netcheck -f csv

Port Scanning

# Scan port range on single host
echo "server.local 1-1024" | netcheck -j 100 > scan-results.txt

# Check common service ports
echo "192.168.1.1 22,80,443,3306,5432,6379,8080,9000" | netcheck

Network Discovery

# Find active hosts in range
cat << EOF | netcheck -j 20
192.168.1.1-254 22
192.168.1.1-254 80
192.168.1.1-254 443
EOF

Combined Scans

# Check multiple subnets with multiple ports
cat << EOF | netcheck -f json -c
192.168.1.0/24 80,443
192.168.2.0/24 80,443
10.0.0.0/24 22,3389
EOF

Data Center Health Check

# Check web servers cluster
echo "web-{01..10}.prod.com 80,443" > servers.txt
# Expand in bash, then check
for i in {1..10}; do echo "web-$(printf %02d $i).prod.com 80,443"; done | netcheck -j 20
# Check every 5 minutes (add to crontab)
*/5 * * * * /usr/local/bin/netcheck /path/to/hosts.txt

Export to Excel

# Generate CSV and open in Excel
netcheck -f csv hosts.txt
libreoffice result.txt

JSON API Integration

# Check and POST results to monitoring API
netcheck -f json hosts.txt
curl -X POST https://api.monitor.com/results \
     -H "Content-Type: application/json" \
     -d @result.txt

Quick Health Check Script

#!/bin/bash
# health-check.sh

CRITICAL_SERVICES=(
    "db.prod.com 3306"
    "api.prod.com 443"
    "cache.prod.com 6379"
)

for service in "${CRITICAL_SERVICES[@]}"; do
    if ! netcheck -q $service > /dev/null 2>&1; then
        echo "ALERT: $service is down!"
        # Send notification
    fi
done

Documentation

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is open-source. See LICENSE file for details.

Author

Network Access Check Tool

Support

  • Report issues on GitHub
  • Check man page: man netcheck
  • See examples: EXAMPLES.md # Send alert email/SMS fi done

## Contributing

Contributions welcome! Please test on your OS and submit pull requests.

## License

GNU General Public License v3 (GPL-3.0)

This project is licensed under GPL v3, which means:
- ✅ Free to use for any purpose
- ✅ Free to modify and improve
- ✅ Free to distribute
- ✅ Can be used commercially
- ⚠️ Any modifications must also be open source (copyleft)
- ⚠️ Cannot create proprietary closed-source versions

See [LICENSE](LICENSE) file for full details.

## Version

Version 1.0.0 - November 2025

Check version: `netcheck -v` or `netcheck --version`

## Documentation

- **[README.md](README.md)** - Main documentation (this file)
- **[EXAMPLES.md](EXAMPLES.md)** - Comprehensive examples and real-world scenarios
- **[INSTALL.md](INSTALL.md)** - Installation instructions
- **[MAKEFILE_GUIDE.md](MAKEFILE_GUIDE.md)** - Understanding the Makefile
- **[DEB_PACKAGING.md](DEB_PACKAGING.md)** - How to create DEB packages
- **[SNAP_PACKAGING.md](SNAP_PACKAGING.md)** - How to create Snap packages
- **[PUBLISHING_GUIDE.md](PUBLISHING_GUIDE.md)** - Quick reference for publishing

## Support

For issues and questions:
- Check `man netcheck` for full documentation
- Run `netcheck --help` for quick reference
- Run `netcheck -v` for version information
- Run `netcheck -d <hostname>` for DNS lookup
- View logs in result.txt and fail-*.txt files
- Report issues on GitHub

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Lightweight network connectivity checker with cross-platform support.

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bash networking network telnet bash-script connectivity-checker

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netcheck v1.2.0 - Network Diagnostics Features Latest
Nov 18, 2025

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