Linux Projects

Troubleshooting Network Connections

File Copying and Updating

Project 3

Troubleshooting Network Connections

Script to troubleshoot networking issues

#!/bin/bash

echo "Checking internet connectivity"
echo

# 1. ping command
echo "Checking with ping..."
# Ping google.com with only 1 packet (-c 1).
if ping -c 1 google.com; then
  echo "Ping successful: Internet is reachable."
else
  echo "Ping failed: Internet is not reachable."
fi
echo

# 2. Establishing TCP connection to port 53
echo "Checking connectivity with nc"
# Try to open a connection to port 53 of www.google.com using /dev/tcp.
# port 53 is the default port for DNS
if nc -zv www.google.com 53 2>&1; then
  echo "Port 53 is open: Internet is reachable."
else
  echo "Port 53 is closed or unreachable: Internet is not reachable."
fi


# 3. nslookup command
echo "Checking connectivity with nslookup..."
# Carry out a DNS lookup for google.com.
if nslookup google.com; then
  echo "nslookup successful: Internet is reachable."
else
  echo "nslookup failed: Internet is not reachable."
fi
echo

# 4. Using the curl command
echo "Checking connectivity with curl..."
# Fetch the HTTP headers of www.google.com using curl, then check if the response is "200 OK".
if curl -Is http://www.google.com | head -n 1 | grep "200 OK" ; then
  echo "HTTP 200 OK: Internet is reachable."
else
  echo "HTTP request failed: Internet is not reachable."
fi
echo

# 5. Using the telnet command
echo "Checking connectivity with telnet..."
# Connect to port 80 of google.com with telnet, then check if "Connected" is present.
if { echo quit; sleep 1; } | telnet google.com 80 2>&1 | grep -q "Connected"; then
  echo "Telnet successful: Internet is reachable."
else
  echo "Telnet failed: Internet is not reachable."
fi
echo

# 6. Using the nmap Command
echo "Checking connectivity with nmap..."
# Scan port 443 of google.com with nmap, to verify if HTTPS services are available, check if port 443 open.
if nmap -p 443 google.com | grep -q "443/tcp open"; then
  echo "Port 443 is open: Internet is reachable."
else
  echo "Port 443 is closed or unreachable: Internet is not reachable."
fi
echo

# 7. With the nc command
echo "Checking connectivity with nc (netcat)..."
# Connect to port 443 of google.com with netcat, then check if "succeeded" is present.
if nc -vz google.com 443 2>&1 | grep -q succeeded; then
  echo "Netcat successful: Internet is reachable."
else
  echo "Netcat failed: Internet is not reachable."
fi
echo

# 8. Using the wget Command
echo "Checking connectivity with wget..."
# Check if http://google.com is reachable without downloading anything.
if wget --spider http://google.com; then
  echo "Wget successful: Internet is reachable."
else
  echo "Wget failed: Internet is not reachable."
fi
echo

echo "Connectivity check completed."

Check the route table

# To show destination networks, gateways, netmask, flags, and interface names
route -n

Check configuration of Firewalls (Redhat and CentOS

#check if firewall is running
sudo firewall-cmd --state

#list all active rules
sudo firewall-cmd --list-all

#list all rules in the filter table with -v verbose output
sudo iptables -L -v -n

Verify if the network is configured as required

# VPN tunnel status
sudo ipsec status

#Verify Network interfaces and IP addresses
ip addr show

#List routes
ip route show

Ensure that the instances themselves are powered on and not experiencing any performance issues

# Check system uptime
uptime

#Processes running
top

#memory usage
free -m

#disk usage
df -h

#check system logs
sudo journalctl -xe

Solutions

# Add a rule to whitelist a specific IP and port
sudo iptables -A INPUT -p tcp -s <SOURCE_IP> --dport <PORT> -j ACCEPT

File Copying and Updating

Setup Script

#!/bin/bash
# Create the source directory if it doesn't exist
mkdir -p source

# Create the changelog.md file with a version entry
echo "Version 1.0.0 - Initial release" > source/changelog.md

# Create the versioninfo.md file with some sample content
echo "This is version 42 of the software." > source/versioninfo.md

# Optionally, create other sample files in the source directory
echo "Sample content for file1.txt" > source/file1.txt
echo "Sample content for file2.txt" > source/file2.txt

# Create the build directory if it doesn't exist
mkdir -p build

echo "Setup complete. You can now run your original script."

New Version Script

#!/bin/bash
#echo "Creating the new version"
firstline=$(head -n 1 source/changelog.md)
read -a splitfirstline <<< $firstline                         
version=${splitfirstline[1]}
echo "Building version" $version
echo 'Do you want to continue? (enter "1" for yes, "0" for no)'
read versioncontinue
if [ $versioncontinue -eq 1 ]
then
  echo "OK"

  # Copy files from source to build
  for filename in source/*
  do
    if [ "$filename" == "source/versioninfo.md" ]
    then
      echo "Copying versioninfo.md with changes"
      # Replace "42" with "43" while copying
      sed 's/42/43/g' $filename > build/versioninfo.md
    else
      echo "Copying" $filename
      cp $filename build/.
    fi
  done

  cd build/
  echo "Build version $version contains:"
  ls
  echo "New version is:"
  cat versioninfo.md

  #retreat
  cd ..
else
  echo "Please, return when you are ready."
fi

Instructions

Save both scripts into a .sh file each.
Change the permissions with chmod +x setup.sh and chmod +x new_version.sh
Run the setup script: ./setup.sh to create the folders and files.
Run the new version script to copy them over to the new folder and apply the change: ./new_version.sh.

Project 3

Updating