Linux Production Shell Scripts

1---
2name: Linux Production Shell Scripts
3description: 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 shell scripts". It provides ready-to-use shell script templates for system administration.
4metadata:
5  author: zebbern
6  version: "1.1"
7---
8 
9# Linux Production Shell Scripts
10 
11## Purpose
12 
13Provide 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.
14 
15## Prerequisites
16 
17### Required Environment
18- Linux/Unix system (bash shell)
19- Appropriate permissions for tasks
20- Required utilities installed (rsync, openssl, etc.)
21 
22### Required Knowledge
23- Basic bash scripting
24- Linux file system structure
25- System administration concepts
26 
27## Outputs and Deliverables
28 
291. **Backup Solutions** - Automated file and database backups
302. **Monitoring Scripts** - Resource usage tracking
313. **Automation Tools** - Scheduled task execution
324. **Security Scripts** - Password management, encryption
33 
34## Core Workflow
35 
36### Phase 1: File Backup Scripts
37 
38**Basic Directory Backup**
39```bash
40#!/bin/bash
41backup_dir="/path/to/backup"
42source_dir="/path/to/source"
43 
44# Create a timestamped backup of the source directory
45tar -czf "$backup_dir/backup_$(date +%Y%m%d_%H%M%S).tar.gz" "$source_dir"
46echo "Backup completed: backup_$(date +%Y%m%d_%H%M%S).tar.gz"
47```
48 
49**Remote Server Backup**
50```bash
51#!/bin/bash
52source_dir="/path/to/source"
53remote_server="user@remoteserver:/path/to/backup"
54 
55# Backup files/directories to a remote server using rsync
56rsync -avz --progress "$source_dir" "$remote_server"
57echo "Files backed up to remote server."
58```
59 
60**Backup Rotation Script**
61```bash
62#!/bin/bash
63backup_dir="/path/to/backups"
64max_backups=5
65 
66# Rotate backups by deleting the oldest if more than max_backups
67while [ $(ls -1 "$backup_dir" | wc -l) -gt "$max_backups" ]; do
68    oldest_backup=$(ls -1t "$backup_dir" | tail -n 1)
69    rm -r "$backup_dir/$oldest_backup"
70    echo "Removed old backup: $oldest_backup"
71done
72echo "Backup rotation completed."
73```
74 
75**Database Backup Script**
76```bash
77#!/bin/bash
78database_name="your_database"
79db_user="username"
80db_pass="password"
81output_file="database_backup_$(date +%Y%m%d).sql"
82 
83# Perform database backup using mysqldump
84mysqldump -u "$db_user" -p"$db_pass" "$database_name" > "$output_file"
85gzip "$output_file"
86echo "Database backup created: $output_file.gz"
87```
88 
89### Phase 2: System Monitoring Scripts
90 
91**CPU Usage Monitor**
92```bash
93#!/bin/bash
94threshold=90
95 
96# Monitor CPU usage and trigger alert if threshold exceeded
97cpu_usage=$(top -bn1 | grep "Cpu(s)" | awk '{print $2}' | cut -d. -f1)
98 
99if [ "$cpu_usage" -gt "$threshold" ]; then
100    echo "ALERT: High CPU usage detected: $cpu_usage%"
101    # Add notification logic (email, slack, etc.)
102    # mail -s "CPU Alert" admin@example.com <<< "CPU usage: $cpu_usage%"
103fi
104```
105 
106**Disk Space Monitor**
107```bash
108#!/bin/bash
109threshold=90
110partition="/dev/sda1"
111 
112# Monitor disk usage and trigger alert if threshold exceeded
113disk_usage=$(df -h | grep "$partition" | awk '{print $5}' | cut -d% -f1)
114 
115if [ "$disk_usage" -gt "$threshold" ]; then
116    echo "ALERT: High disk usage detected: $disk_usage%"
117    # Add alert/notification logic here
118fi
119```
120 
121**CPU Usage Logger**
122```bash
123#!/bin/bash
124output_file="cpu_usage_log.txt"
125 
126# Log current CPU usage to a file with timestamp
127timestamp=$(date '+%Y-%m-%d %H:%M:%S')
128cpu_usage=$(top -bn1 | grep 'Cpu(s)' | awk '{print $2}' | cut -d. -f1)
129echo "$timestamp - CPU Usage: $cpu_usage%" >> "$output_file"
130echo "CPU usage logged."
131```
132 
133**System Health Check**
134```bash
135#!/bin/bash
136output_file="system_health_check.txt"
137 
138# Perform system health check and save results to a file
139{
140    echo "System Health Check - $(date)"
141    echo "================================"
142    echo ""
143    echo "Uptime:"
144    uptime
145    echo ""
146    echo "Load Average:"
147    cat /proc/loadavg
148    echo ""
149    echo "Memory Usage:"
150    free -h
151    echo ""
152    echo "Disk Usage:"
153    df -h
154    echo ""
155    echo "Top Processes:"
156    ps aux --sort=-%cpu | head -10
157} > "$output_file"
158 
159echo "System health check saved to $output_file"
160```
161 
162### Phase 3: User Management Scripts
163 
164**User Account Creation**
165```bash
166#!/bin/bash
167username="newuser"
168 
169# Check if user exists; if not, create new user
170if id "$username" &>/dev/null; then
171    echo "User $username already exists."
172else
173    useradd -m -s /bin/bash "$username"
174    echo "User $username created."
175    
176    # Set password interactively
177    passwd "$username"
178fi
179```
180 
181**Password Expiry Checker**
182```bash
183#!/bin/bash
184output_file="password_expiry_report.txt"
185 
186# Check password expiry for users with bash shell
187echo "Password Expiry Report - $(date)" > "$output_file"
188echo "=================================" >> "$output_file"
189 
190IFS=$'\n'
191for user in $(grep "/bin/bash" /etc/passwd | cut -d: -f1); do
192    password_expires=$(chage -l "$user" 2>/dev/null | grep "Password expires" | awk -F: '{print $2}')
193    echo "User: $user - Password Expires: $password_expires" >> "$output_file"
194done
195unset IFS
196 
197echo "Password expiry report saved to $output_file"
198```
199 
200### Phase 4: Security Scripts
201 
202**Password Generator**
203```bash
204#!/bin/bash
205length=${1:-16}
206 
207# Generate a random password
208password=$(openssl rand -base64 48 | tr -dc 'a-zA-Z0-9!@#$%^&*' | head -c"$length")
209echo "Generated password: $password"
210```
211 
212**File Encryption Script**
213```bash
214#!/bin/bash
215file="$1"
216action="${2:-encrypt}"
217 
218if [ -z "$file" ]; then
219    echo "Usage: $0 <file> [encrypt|decrypt]"
220    exit 1
221fi
222 
223if [ "$action" == "encrypt" ]; then
224    # Encrypt file using AES-256-CBC
225    openssl enc -aes-256-cbc -salt -pbkdf2 -in "$file" -out "$file.enc"
226    echo "File encrypted: $file.enc"
227elif [ "$action" == "decrypt" ]; then
228    # Decrypt file
229    output_file="${file%.enc}"
230    openssl enc -aes-256-cbc -d -pbkdf2 -in "$file" -out "$output_file"
231    echo "File decrypted: $output_file"
232fi
233```
234 
235### Phase 5: Log Analysis Scripts
236 
237**Error Log Extractor**
238```bash
239#!/bin/bash
240logfile="${1:-/var/log/syslog}"
241output_file="error_log_$(date +%Y%m%d).txt"
242 
243# Extract lines with "ERROR" from the log file
244grep -i "error\|fail\|critical" "$logfile" > "$output_file"
245echo "Error log created: $output_file"
246echo "Total errors found: $(wc -l < "$output_file")"
247```
248 
249**Web Server Log Analyzer**
250```bash
251#!/bin/bash
252log_file="${1:-/var/log/apache2/access.log}"
253 
254echo "Web Server Log Analysis"
255echo "========================"
256echo ""
257echo "Top 10 IP Addresses:"
258awk '{print $1}' "$log_file" | sort | uniq -c | sort -rn | head -10
259echo ""
260echo "Top 10 Requested URLs:"
261awk '{print $7}' "$log_file" | sort | uniq -c | sort -rn | head -10
262echo ""
263echo "HTTP Status Code Distribution:"
264awk '{print $9}' "$log_file" | sort | uniq -c | sort -rn
265```
266 
267### Phase 6: Network Scripts
268 
269**Network Connectivity Checker**
270```bash
271#!/bin/bash
272hosts=("8.8.8.8" "1.1.1.1" "google.com")
273 
274echo "Network Connectivity Check"
275echo "=========================="
276 
277for host in "${hosts[@]}"; do
278    if ping -c 1 -W 2 "$host" &>/dev/null; then
279        echo "[UP] $host is reachable"
280    else
281        echo "[DOWN] $host is unreachable"
282    fi
283done
284```
285 
286**Website Uptime Checker**
287```bash
288#!/bin/bash
289websites=("https://google.com" "https://github.com")
290log_file="uptime_log.txt"
291 
292echo "Website Uptime Check - $(date)" >> "$log_file"
293 
294for website in "${websites[@]}"; do
295    if curl --output /dev/null --silent --head --fail --max-time 10 "$website"; then
296        echo "[UP] $website is accessible" | tee -a "$log_file"
297    else
298        echo "[DOWN] $website is inaccessible" | tee -a "$log_file"
299    fi
300done
301```
302 
303**Network Interface Info**
304```bash
305#!/bin/bash
306interface="${1:-eth0}"
307 
308echo "Network Interface Information: $interface"
309echo "========================================="
310ip addr show "$interface" 2>/dev/null || ifconfig "$interface" 2>/dev/null
311echo ""
312echo "Routing Table:"
313ip route | grep "$interface"
314```
315 
316### Phase 7: Automation Scripts
317 
318**Automated Package Installation**
319```bash
320#!/bin/bash
321packages=("vim" "htop" "curl" "wget" "git")
322 
323echo "Installing packages..."
324 
325for package in "${packages[@]}"; do
326    if dpkg -l | grep -q "^ii  $package"; then
327        echo "[SKIP] $package is already installed"
328    else
329        sudo apt-get install -y "$package"
330        echo "[INSTALLED] $package"
331    fi
332done
333 
334echo "Package installation completed."
335```
336 
337**Task Scheduler (Cron Setup)**
338```bash
339#!/bin/bash
340scheduled_task="/path/to/your_script.sh"
341schedule_time="0 2 * * *"  # Run at 2 AM daily
342 
343# Add task to crontab
344(crontab -l 2>/dev/null; echo "$schedule_time $scheduled_task") | crontab -
345echo "Task scheduled: $schedule_time $scheduled_task"
346```
347 
348**Service Restart Script**
349```bash
350#!/bin/bash
351service_name="${1:-apache2}"
352 
353# Restart a specified service
354if systemctl is-active --quiet "$service_name"; then
355    echo "Restarting $service_name..."
356    sudo systemctl restart "$service_name"
357    echo "Service $service_name restarted."
358else
359    echo "Service $service_name is not running. Starting..."
360    sudo systemctl start "$service_name"
361    echo "Service $service_name started."
362fi
363```
364 
365### Phase 8: File Operations
366 
367**Directory Synchronization**
368```bash
369#!/bin/bash
370source_dir="/path/to/source"
371destination_dir="/path/to/destination"
372 
373# Synchronize directories using rsync
374rsync -avz --delete "$source_dir/" "$destination_dir/"
375echo "Directories synchronized successfully."
376```
377 
378**Data Cleanup Script**
379```bash
380#!/bin/bash
381directory="${1:-/tmp}"
382days="${2:-7}"
383 
384echo "Cleaning files older than $days days in $directory"
385 
386# Remove files older than specified days
387find "$directory" -type f -mtime +"$days" -exec rm -v {} \;
388echo "Cleanup completed."
389```
390 
391**Folder Size Checker**
392```bash
393#!/bin/bash
394folder_path="${1:-.}"
395 
396echo "Folder Size Analysis: $folder_path"
397echo "===================================="
398 
399# Display sizes of subdirectories sorted by size
400du -sh "$folder_path"/* 2>/dev/null | sort -rh | head -20
401echo ""
402echo "Total size:"
403du -sh "$folder_path"
404```
405 
406### Phase 9: System Information
407 
408**System Info Collector**
409```bash
410#!/bin/bash
411output_file="system_info_$(hostname)_$(date +%Y%m%d).txt"
412 
413{
414    echo "System Information Report"
415    echo "Generated: $(date)"
416    echo "========================="
417    echo ""
418    echo "Hostname: $(hostname)"
419    echo "OS: $(uname -a)"
420    echo ""
421    echo "CPU Info:"
422    lscpu | grep -E "Model name|CPU\(s\)|Thread"
423    echo ""
424    echo "Memory:"
425    free -h
426    echo ""
427    echo "Disk Space:"
428    df -h
429    echo ""
430    echo "Network Interfaces:"
431    ip -br addr
432    echo ""
433    echo "Logged In Users:"
434    who
435} > "$output_file"
436 
437echo "System info saved to $output_file"
438```
439 
440### Phase 10: Git and Development
441 
442**Git Repository Updater**
443```bash
444#!/bin/bash
445git_repos=("/path/to/repo1" "/path/to/repo2")
446 
447for repo in "${git_repos[@]}"; do
448    if [ -d "$repo/.git" ]; then
449        echo "Updating repository: $repo"
450        cd "$repo"
451        git fetch --all
452        git pull origin "$(git branch --show-current)"
453        echo "Updated: $repo"
454    else
455        echo "Not a git repository: $repo"
456    fi
457done
458 
459echo "All repositories updated."
460```
461 
462**Remote Script Execution**
463```bash
464#!/bin/bash
465remote_server="${1:-user@remote-server}"
466remote_script="${2:-/path/to/remote/script.sh}"
467 
468# Execute a script on a remote server via SSH
469ssh "$remote_server" "bash -s" < "$remote_script"
470echo "Remote script executed on $remote_server"
471```
472 
473## Quick Reference
474 
475### Common Script Patterns
476 
477| Pattern | Purpose |
478|---------|---------|
479| `#!/bin/bash` | Shebang for bash |
480| `$(date +%Y%m%d)` | Date formatting |
481| `$((expression))` | Arithmetic |
482| `${var:-default}` | Default value |
483| `"$@"` | All arguments |
484 
485### Useful Commands
486 
487| Command | Purpose |
488|---------|---------|
489| `chmod +x script.sh` | Make executable |
490| `./script.sh` | Run script |
491| `nohup ./script.sh &` | Run in background |
492| `crontab -e` | Edit cron jobs |
493| `source script.sh` | Run in current shell |
494 
495### Cron Format
496Minute(0-59) Hour(0-23) Day(1-31) Month(1-12) Weekday(0-7, 0/7=Sun)
497 
498## Constraints and Limitations
499 
500- Always test scripts in non-production first
501- Use absolute paths to avoid errors
502- Quote variables to handle spaces properly
503- Many scripts require root/sudo privileges
504- Use `bash -x script.sh` for debugging
505