Linux Production Shell Scripts

Purpose

Provide production-ready shell script templates for common Linux system administration tasks including backups, monitoring, user management, log analysis, and automation. These scripts serve as building blocks for security operations and penetration testing environments.

Prerequisites

Required Environment

• Linux/Unix system (bash shell)

• Appropriate permissions for tasks

• Required utilities installed (rsync, openssl, etc.)

Required Knowledge

• Basic bash scripting

• Linux file system structure

• System administration concepts

Outputs and Deliverables

• Backup Solutions - Automated file and database backups

• Monitoring Scripts - Resource usage tracking

• Automation Tools - Scheduled task execution

• Security Scripts - Password management, encryption

Core Workflow

Phase 1: File Backup Scripts

Basic Directory Backup

#!/bin/bash backup_dir="/path/to/backup" source_dir="/path/to/source"

Create a timestamped backup of the source directory

tar -czf "$backup_dir/backup_$(date +%Y%m%d_%H%M%S).tar.gz" "$source_dir" echo "Backup completed: backup_$(date +%Y%m%d_%H%M%S).tar.gz"

Remote Server Backup

#!/bin/bash source_dir="/path/to/source" remote_server="user@remoteserver:/path/to/backup"

Backup files/directories to a remote server using rsync

rsync -avz --progress "$source_dir" "$remote_server" echo "Files backed up to remote server."

Backup Rotation Script

#!/bin/bash backup_dir="/path/to/backups" max_backups=5

Rotate backups by deleting the oldest if more than max_backups

while [ $(ls -1 "$backup_dir" | wc -l) -gt "$max_backups" ]; do oldest_backup=$(ls -1t "$backup_dir" | tail -n 1) rm -r "$backup_dir/$oldest_backup" echo "Removed old backup: $oldest_backup" done echo "Backup rotation completed."

Database Backup Script

#!/bin/bash database_name="your_database" db_user="username" db_pass="password" output_file="database_backup_$(date +%Y%m%d).sql"

Perform database backup using mysqldump

mysqldump -u "$db_user" -p"$db_pass" "$database_name" > "$output_file" gzip "$output_file" echo "Database backup created: $output_file.gz"

Phase 2: System Monitoring Scripts

CPU Usage Monitor

#!/bin/bash threshold=90

Monitor CPU usage and trigger alert if threshold exceeded

cpu_usage=$(top -bn1 | grep "Cpu(s)" | awk '{print $2}' | cut -d. -f1)

if [ "$cpu_usage" -gt "$threshold" ]; then echo "ALERT: High CPU usage detected: $cpu_usage%" # Add notification logic (email, slack, etc.) # mail -s "CPU Alert" admin@example.com <<< "CPU usage: $cpu_usage%" fi

Disk Space Monitor

#!/bin/bash threshold=90 partition="/dev/sda1"

Monitor disk usage and trigger alert if threshold exceeded

disk_usage=$(df -h | grep "$partition" | awk '{print $5}' | cut -d% -f1)

if [ "$disk_usage" -gt "$threshold" ]; then echo "ALERT: High disk usage detected: $disk_usage%" # Add alert/notification logic here fi

CPU Usage Logger

#!/bin/bash output_file="cpu_usage_log.txt"

Log current CPU usage to a file with timestamp

timestamp=$(date '+%Y-%m-%d %H:%M:%S') cpu_usage=$(top -bn1 | grep 'Cpu(s)' | awk '{print $2}' | cut -d. -f1) echo "$timestamp - CPU Usage: $cpu_usage%" >> "$output_file" echo "CPU usage logged."

System Health Check

#!/bin/bash output_file="system_health_check.txt"

Perform system health check and save results to a file

{ echo "System Health Check - $(date)" echo "================================" echo "" echo "Uptime:" uptime echo "" echo "Load Average:" cat /proc/loadavg echo "" echo "Memory Usage:" free -h echo "" echo "Disk Usage:" df -h echo "" echo "Top Processes:" ps aux --sort=-%cpu | head -10 } > "$output_file"

echo "System health check saved to $output_file"

Phase 3: User Management Scripts

User Account Creation

#!/bin/bash username="newuser"

Check if user exists; if not, create new user

if id "$username" &>/dev/null; then echo "User $username already exists." else useradd -m -s /bin/bash "$username" echo "User $username created."

# Set password interactively
passwd "$username"

fi

Password Expiry Checker

#!/bin/bash output_file="password_expiry_report.txt"

Check password expiry for users with bash shell

echo "Password Expiry Report - $(date)" > "$output_file" echo "=================================" >> "$output_file"

IFS=$'\n' for user in $(grep "/bin/bash" /etc/passwd | cut -d: -f1); do password_expires=$(chage -l "$user" 2>/dev/null | grep "Password expires" | awk -F: '{print $2}') echo "User: $user - Password Expires: $password_expires" >> "$output_file" done unset IFS

echo "Password expiry report saved to $output_file"

Phase 4: Security Scripts

Password Generator

#!/bin/bash length=${1:-16}

Generate a random password

password=$(openssl rand -base64 48 | tr -dc 'a-zA-Z0-9!@#$%^&*' | head -c"$length") echo "Generated password: $password"

File Encryption Script

#!/bin/bash file="$1" action="${2:-encrypt}"

if [ -z "$file" ]; then echo "Usage: $0 <file> [encrypt|decrypt]" exit 1 fi

if [ "$action" == "encrypt" ]; then # Encrypt file using AES-256-CBC openssl enc -aes-256-cbc -salt -pbkdf2 -in "$file" -out "$file.enc" echo "File encrypted: $file.enc" elif [ "$action" == "decrypt" ]; then # Decrypt file output_file="${file%.enc}" openssl enc -aes-256-cbc -d -pbkdf2 -in "$file" -out "$output_file" echo "File decrypted: $output_file" fi

Phase 5: Log Analysis Scripts

Error Log Extractor

#!/bin/bash logfile="${1:-/var/log/syslog}" output_file="error_log_$(date +%Y%m%d).txt"

Extract lines with "ERROR" from the log file

grep -i "error|fail|critical" "$logfile" > "$output_file" echo "Error log created: $output_file" echo "Total errors found: $(wc -l < "$output_file")"

Web Server Log Analyzer

#!/bin/bash log_file="${1:-/var/log/apache2/access.log}"

echo "Web Server Log Analysis" echo "========================" echo "" echo "Top 10 IP Addresses:" awk '{print $1}' "$log_file" | sort | uniq -c | sort -rn | head -10 echo "" echo "Top 10 Requested URLs:" awk '{print $7}' "$log_file" | sort | uniq -c | sort -rn | head -10 echo "" echo "HTTP Status Code Distribution:" awk '{print $9}' "$log_file" | sort | uniq -c | sort -rn

Phase 6: Network Scripts

Network Connectivity Checker

#!/bin/bash hosts=("8.8.8.8" "1.1.1.1" "google.com")

echo "Network Connectivity Check" echo "=========================="

for host in "${hosts[@]}"; do if ping -c 1 -W 2 "$host" &>/dev/null; then echo "[UP] $host is reachable" else echo "[DOWN] $host is unreachable" fi done

Website Uptime Checker

#!/bin/bash websites=("https://google.com" "https://github.com") log_file="uptime_log.txt"

echo "Website Uptime Check - $(date)" >> "$log_file"

for website in "${websites[@]}"; do if curl --output /dev/null --silent --head --fail --max-time 10 "$website"; then echo "[UP] $website is accessible" | tee -a "$log_file" else echo "[DOWN] $website is inaccessible" | tee -a "$log_file" fi done

Network Interface Info

#!/bin/bash interface="${1:-eth0}"

echo "Network Interface Information: $interface" echo "=========================================" ip addr show "$interface" 2>/dev/null || ifconfig "$interface" 2>/dev/null echo "" echo "Routing Table:" ip route | grep "$interface"

Phase 7: Automation Scripts

Automated Package Installation

#!/bin/bash packages=("vim" "htop" "curl" "wget" "git")

echo "Installing packages..."

for package in "${packages[@]}"; do if dpkg -l | grep -q "^ii $package"; then echo "[SKIP] $package is already installed" else sudo apt-get install -y "$package" echo "[INSTALLED] $package" fi done

echo "Package installation completed."

Task Scheduler (Cron Setup)

#!/bin/bash scheduled_task="/path/to/your_script.sh" schedule_time="0 2 * * *" # Run at 2 AM daily

Add task to crontab

(crontab -l 2>/dev/null; echo "$schedule_time $scheduled_task") | crontab - echo "Task scheduled: $schedule_time $scheduled_task"

Service Restart Script

#!/bin/bash service_name="${1:-apache2}"

Restart a specified service

if systemctl is-active --quiet "$service_name"; then echo "Restarting $service_name..." sudo systemctl restart "$service_name" echo "Service $service_name restarted." else echo "Service $service_name is not running. Starting..." sudo systemctl start "$service_name" echo "Service $service_name started." fi

Phase 8: File Operations

Directory Synchronization

#!/bin/bash source_dir="/path/to/source" destination_dir="/path/to/destination"

Synchronize directories using rsync

rsync -avz --delete "$source_dir/" "$destination_dir/" echo "Directories synchronized successfully."

Data Cleanup Script

#!/bin/bash directory="${1:-/tmp}" days="${2:-7}"

echo "Cleaning files older than $days days in $directory"

Remove files older than specified days

find "$directory" -type f -mtime +"$days" -exec rm -v {} ; echo "Cleanup completed."

Folder Size Checker

#!/bin/bash folder_path="${1:-.}"

echo "Folder Size Analysis: $folder_path" echo "===================================="

Display sizes of subdirectories sorted by size

du -sh "$folder_path"/* 2>/dev/null | sort -rh | head -20 echo "" echo "Total size:" du -sh "$folder_path"

Phase 9: System Information

System Info Collector

#!/bin/bash output_file="system_info_$(hostname)_$(date +%Y%m%d).txt"

{ echo "System Information Report" echo "Generated: $(date)" echo "=========================" echo "" echo "Hostname: $(hostname)" echo "OS: $(uname -a)" echo "" echo "CPU Info:" lscpu | grep -E "Model name|CPU(s)|Thread" echo "" echo "Memory:" free -h echo "" echo "Disk Space:" df -h echo "" echo "Network Interfaces:" ip -br addr echo "" echo "Logged In Users:" who } > "$output_file"

echo "System info saved to $output_file"

Phase 10: Git and Development

Git Repository Updater

#!/bin/bash git_repos=("/path/to/repo1" "/path/to/repo2")

for repo in "${git_repos[@]}"; do if [ -d "$repo/.git" ]; then echo "Updating repository: $repo" cd "$repo" git fetch --all git pull origin "$(git branch --show-current)" echo "Updated: $repo" else echo "Not a git repository: $repo" fi done

echo "All repositories updated."

Remote Script Execution

#!/bin/bash remote_server="${1:-user@remote-server}" remote_script="${2:-/path/to/remote/script.sh}"

Execute a script on a remote server via SSH

ssh "$remote_server" "bash -s" < "$remote_script" echo "Remote script executed on $remote_server"

Quick Reference

Common Script Patterns

Pattern Purpose

#!/bin/bash

Shebang for bash

$(date +%Y%m%d)

Date formatting

$((expression))

Arithmetic

${var:-default}

Default value

"$@"

All arguments

Useful Commands

Command Purpose

chmod +x script.sh

Make executable

./script.sh

Run script

nohup ./script.sh &

Run in background

crontab -e

Edit cron jobs

source script.sh

Run in current shell

Cron Format

Minute(0-59) Hour(0-23) Day(1-31) Month(1-12) Weekday(0-7, 0/7=Sun)

Constraints and Limitations

• Always test scripts in non-production first

• Use absolute paths to avoid errors

• Quote variables to handle spaces properly

• Many scripts require root/sudo privileges

• Use bash -x script.sh for debugging