508 lines
12 KiB
Markdown
508 lines
12 KiB
Markdown
---
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name: linux-shell-scripting
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description: "This skill should be used when the user asks to \"create bash scripts\", \"automate Linux tasks\", \"monitor system resources\", \"backup files\", \"manage users\", or \"write production she..."
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risk: unknown
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source: community
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date_added: "2026-02-27"
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---
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# Linux Production Shell Scripts
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## Purpose
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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.
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## Prerequisites
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### Required Environment
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- Linux/Unix system (bash shell)
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- Appropriate permissions for tasks
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- Required utilities installed (rsync, openssl, etc.)
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### Required Knowledge
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- Basic bash scripting
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- Linux file system structure
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- System administration concepts
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## Outputs and Deliverables
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1. **Backup Solutions** - Automated file and database backups
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2. **Monitoring Scripts** - Resource usage tracking
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3. **Automation Tools** - Scheduled task execution
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4. **Security Scripts** - Password management, encryption
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## Core Workflow
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### Phase 1: File Backup Scripts
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**Basic Directory Backup**
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```bash
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#!/bin/bash
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backup_dir="/path/to/backup"
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source_dir="/path/to/source"
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# Create a timestamped backup of the source directory
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tar -czf "$backup_dir/backup_$(date +%Y%m%d_%H%M%S).tar.gz" "$source_dir"
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echo "Backup completed: backup_$(date +%Y%m%d_%H%M%S).tar.gz"
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```
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**Remote Server Backup**
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```bash
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#!/bin/bash
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source_dir="/path/to/source"
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remote_server="user@remoteserver:/path/to/backup"
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# Backup files/directories to a remote server using rsync
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rsync -avz --progress "$source_dir" "$remote_server"
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echo "Files backed up to remote server."
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```
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**Backup Rotation Script**
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```bash
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#!/bin/bash
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backup_dir="/path/to/backups"
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max_backups=5
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# Rotate backups by deleting the oldest if more than max_backups
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while [ $(ls -1 "$backup_dir" | wc -l) -gt "$max_backups" ]; do
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oldest_backup=$(ls -1t "$backup_dir" | tail -n 1)
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rm -r "$backup_dir/$oldest_backup"
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echo "Removed old backup: $oldest_backup"
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done
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echo "Backup rotation completed."
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```
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**Database Backup Script**
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```bash
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#!/bin/bash
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database_name="your_database"
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db_user="username"
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db_pass="password"
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output_file="database_backup_$(date +%Y%m%d).sql"
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# Perform database backup using mysqldump
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mysqldump -u "$db_user" -p"$db_pass" "$database_name" > "$output_file"
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gzip "$output_file"
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echo "Database backup created: $output_file.gz"
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```
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### Phase 2: System Monitoring Scripts
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**CPU Usage Monitor**
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```bash
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#!/bin/bash
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threshold=90
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# Monitor CPU usage and trigger alert if threshold exceeded
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cpu_usage=$(top -bn1 | grep "Cpu(s)" | awk '{print $2}' | cut -d. -f1)
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if [ "$cpu_usage" -gt "$threshold" ]; then
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echo "ALERT: High CPU usage detected: $cpu_usage%"
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# Add notification logic (email, slack, etc.)
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# mail -s "CPU Alert" admin@example.com <<< "CPU usage: $cpu_usage%"
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fi
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```
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**Disk Space Monitor**
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```bash
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#!/bin/bash
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threshold=90
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partition="/dev/sda1"
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# Monitor disk usage and trigger alert if threshold exceeded
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disk_usage=$(df -h | grep "$partition" | awk '{print $5}' | cut -d% -f1)
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if [ "$disk_usage" -gt "$threshold" ]; then
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echo "ALERT: High disk usage detected: $disk_usage%"
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# Add alert/notification logic here
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fi
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```
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**CPU Usage Logger**
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```bash
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#!/bin/bash
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output_file="cpu_usage_log.txt"
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# Log current CPU usage to a file with timestamp
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timestamp=$(date '+%Y-%m-%d %H:%M:%S')
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cpu_usage=$(top -bn1 | grep 'Cpu(s)' | awk '{print $2}' | cut -d. -f1)
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echo "$timestamp - CPU Usage: $cpu_usage%" >> "$output_file"
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echo "CPU usage logged."
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```
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**System Health Check**
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```bash
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#!/bin/bash
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output_file="system_health_check.txt"
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# Perform system health check and save results to a file
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{
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echo "System Health Check - $(date)"
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echo "================================"
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echo ""
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echo "Uptime:"
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uptime
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echo ""
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echo "Load Average:"
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cat /proc/loadavg
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echo ""
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echo "Memory Usage:"
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free -h
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echo ""
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echo "Disk Usage:"
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df -h
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echo ""
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echo "Top Processes:"
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ps aux --sort=-%cpu | head -10
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} > "$output_file"
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echo "System health check saved to $output_file"
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```
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### Phase 3: User Management Scripts
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**User Account Creation**
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```bash
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#!/bin/bash
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username="newuser"
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# Check if user exists; if not, create new user
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if id "$username" &>/dev/null; then
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echo "User $username already exists."
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else
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useradd -m -s /bin/bash "$username"
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echo "User $username created."
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# Set password interactively
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passwd "$username"
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fi
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```
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**Password Expiry Checker**
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```bash
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#!/bin/bash
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output_file="password_expiry_report.txt"
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# Check password expiry for users with bash shell
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echo "Password Expiry Report - $(date)" > "$output_file"
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echo "=================================" >> "$output_file"
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IFS=$'\n'
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for user in $(grep "/bin/bash" /etc/passwd | cut -d: -f1); do
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password_expires=$(chage -l "$user" 2>/dev/null | grep "Password expires" | awk -F: '{print $2}')
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echo "User: $user - Password Expires: $password_expires" >> "$output_file"
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done
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unset IFS
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echo "Password expiry report saved to $output_file"
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```
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### Phase 4: Security Scripts
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**Password Generator**
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```bash
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#!/bin/bash
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length=${1:-16}
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# Generate a random password
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password=$(openssl rand -base64 48 | tr -dc 'a-zA-Z0-9!@#$%^&*' | head -c"$length")
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echo "Generated password: $password"
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```
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**File Encryption Script**
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```bash
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#!/bin/bash
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file="$1"
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action="${2:-encrypt}"
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if [ -z "$file" ]; then
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echo "Usage: $0 <file> [encrypt|decrypt]"
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exit 1
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fi
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if [ "$action" == "encrypt" ]; then
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# Encrypt file using AES-256-CBC
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openssl enc -aes-256-cbc -salt -pbkdf2 -in "$file" -out "$file.enc"
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echo "File encrypted: $file.enc"
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elif [ "$action" == "decrypt" ]; then
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# Decrypt file
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output_file="${file%.enc}"
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openssl enc -aes-256-cbc -d -pbkdf2 -in "$file" -out "$output_file"
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echo "File decrypted: $output_file"
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fi
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```
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### Phase 5: Log Analysis Scripts
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**Error Log Extractor**
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```bash
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#!/bin/bash
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logfile="${1:-/var/log/syslog}"
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output_file="error_log_$(date +%Y%m%d).txt"
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# Extract lines with "ERROR" from the log file
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grep -i "error\|fail\|critical" "$logfile" > "$output_file"
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echo "Error log created: $output_file"
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echo "Total errors found: $(wc -l < "$output_file")"
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```
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**Web Server Log Analyzer**
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```bash
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#!/bin/bash
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log_file="${1:-/var/log/apache2/access.log}"
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echo "Web Server Log Analysis"
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echo "========================"
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echo ""
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echo "Top 10 IP Addresses:"
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awk '{print $1}' "$log_file" | sort | uniq -c | sort -rn | head -10
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echo ""
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echo "Top 10 Requested URLs:"
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awk '{print $7}' "$log_file" | sort | uniq -c | sort -rn | head -10
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echo ""
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echo "HTTP Status Code Distribution:"
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awk '{print $9}' "$log_file" | sort | uniq -c | sort -rn
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```
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### Phase 6: Network Scripts
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**Network Connectivity Checker**
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```bash
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#!/bin/bash
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hosts=("8.8.8.8" "1.1.1.1" "google.com")
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echo "Network Connectivity Check"
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echo "=========================="
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for host in "${hosts[@]}"; do
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if ping -c 1 -W 2 "$host" &>/dev/null; then
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echo "[UP] $host is reachable"
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else
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echo "[DOWN] $host is unreachable"
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fi
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done
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```
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**Website Uptime Checker**
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```bash
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#!/bin/bash
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websites=("https://google.com" "https://github.com")
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log_file="uptime_log.txt"
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echo "Website Uptime Check - $(date)" >> "$log_file"
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for website in "${websites[@]}"; do
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if curl --output /dev/null --silent --head --fail --max-time 10 "$website"; then
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echo "[UP] $website is accessible" | tee -a "$log_file"
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else
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echo "[DOWN] $website is inaccessible" | tee -a "$log_file"
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fi
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done
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```
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**Network Interface Info**
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```bash
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#!/bin/bash
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interface="${1:-eth0}"
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echo "Network Interface Information: $interface"
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echo "========================================="
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ip addr show "$interface" 2>/dev/null || ifconfig "$interface" 2>/dev/null
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echo ""
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echo "Routing Table:"
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ip route | grep "$interface"
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```
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### Phase 7: Automation Scripts
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**Automated Package Installation**
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```bash
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#!/bin/bash
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packages=("vim" "htop" "curl" "wget" "git")
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echo "Installing packages..."
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for package in "${packages[@]}"; do
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if dpkg -l | grep -q "^ii $package"; then
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echo "[SKIP] $package is already installed"
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else
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sudo apt-get install -y "$package"
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echo "[INSTALLED] $package"
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fi
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done
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echo "Package installation completed."
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```
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**Task Scheduler (Cron Setup)**
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```bash
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#!/bin/bash
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scheduled_task="/path/to/your_script.sh"
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schedule_time="0 2 * * *" # Run at 2 AM daily
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# Add task to crontab
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(crontab -l 2>/dev/null; echo "$schedule_time $scheduled_task") | crontab -
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echo "Task scheduled: $schedule_time $scheduled_task"
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```
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**Service Restart Script**
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```bash
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#!/bin/bash
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service_name="${1:-apache2}"
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# Restart a specified service
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if systemctl is-active --quiet "$service_name"; then
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echo "Restarting $service_name..."
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sudo systemctl restart "$service_name"
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echo "Service $service_name restarted."
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else
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echo "Service $service_name is not running. Starting..."
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sudo systemctl start "$service_name"
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echo "Service $service_name started."
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fi
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```
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### Phase 8: File Operations
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**Directory Synchronization**
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```bash
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#!/bin/bash
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source_dir="/path/to/source"
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destination_dir="/path/to/destination"
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# Synchronize directories using rsync
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rsync -avz --delete "$source_dir/" "$destination_dir/"
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echo "Directories synchronized successfully."
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```
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**Data Cleanup Script**
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```bash
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#!/bin/bash
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directory="${1:-/tmp}"
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days="${2:-7}"
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echo "Cleaning files older than $days days in $directory"
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# Remove files older than specified days
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find "$directory" -type f -mtime +"$days" -exec rm -v {} \;
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echo "Cleanup completed."
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```
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**Folder Size Checker**
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```bash
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#!/bin/bash
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folder_path="${1:-.}"
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echo "Folder Size Analysis: $folder_path"
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echo "===================================="
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# Display sizes of subdirectories sorted by size
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du -sh "$folder_path"/* 2>/dev/null | sort -rh | head -20
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echo ""
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echo "Total size:"
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du -sh "$folder_path"
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```
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### Phase 9: System Information
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**System Info Collector**
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```bash
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#!/bin/bash
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output_file="system_info_$(hostname)_$(date +%Y%m%d).txt"
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{
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echo "System Information Report"
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echo "Generated: $(date)"
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echo "========================="
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echo ""
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echo "Hostname: $(hostname)"
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echo "OS: $(uname -a)"
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echo ""
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echo "CPU Info:"
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lscpu | grep -E "Model name|CPU\(s\)|Thread"
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echo ""
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echo "Memory:"
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free -h
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echo ""
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echo "Disk Space:"
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df -h
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echo ""
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echo "Network Interfaces:"
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ip -br addr
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echo ""
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echo "Logged In Users:"
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who
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} > "$output_file"
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echo "System info saved to $output_file"
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```
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### Phase 10: Git and Development
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**Git Repository Updater**
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```bash
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#!/bin/bash
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git_repos=("/path/to/repo1" "/path/to/repo2")
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for repo in "${git_repos[@]}"; do
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if [ -d "$repo/.git" ]; then
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echo "Updating repository: $repo"
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cd "$repo"
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git fetch --all
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git pull origin "$(git branch --show-current)"
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echo "Updated: $repo"
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else
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echo "Not a git repository: $repo"
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fi
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done
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echo "All repositories updated."
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```
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**Remote Script Execution**
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```bash
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#!/bin/bash
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remote_server="${1:-user@remote-server}"
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remote_script="${2:-/path/to/remote/script.sh}"
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# Execute a script on a remote server via SSH
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ssh "$remote_server" "bash -s" < "$remote_script"
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echo "Remote script executed on $remote_server"
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```
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## Quick Reference
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### Common Script Patterns
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| Pattern | Purpose |
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|---------|---------|
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| `#!/bin/bash` | Shebang for bash |
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| `$(date +%Y%m%d)` | Date formatting |
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| `$((expression))` | Arithmetic |
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| `${var:-default}` | Default value |
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| `"$@"` | All arguments |
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### Useful Commands
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| Command | Purpose |
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|---------|---------|
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| `chmod +x script.sh` | Make executable |
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| `./script.sh` | Run script |
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| `nohup ./script.sh &` | Run in background |
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| `crontab -e` | Edit cron jobs |
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| `source script.sh` | Run in current shell |
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### Cron Format
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Minute(0-59) Hour(0-23) Day(1-31) Month(1-12) Weekday(0-7, 0/7=Sun)
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## Constraints and Limitations
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- Always test scripts in non-production first
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- Use absolute paths to avoid errors
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- Quote variables to handle spaces properly
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- Many scripts require root/sudo privileges
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- Use `bash -x script.sh` for debugging
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## When to Use
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This skill is applicable to execute the workflow or actions described in the overview.
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