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Shell Scripting useful for Production

A shell script is a text file containing a series of commands that are executed by a Unix/Linux shell (command-line interpreter). It automates repetitive tasks, combines multiple commands, and can include programming constructs like loops, conditionals, and functions.

Key Features of Shell Scripting:

  1. Automation — Runs commands without manual input.
  2. Batch Processing — Executes multiple commands sequentially.
  3. Scripting Language — Supports variables, loops, and conditionals.
  4. Reusability — Scripts can be saved and reused.
  5. Customization — Can take user input and generate dynamic output.

1. Backup Script 

mkdir source
touch /source/1.txt /source/2.txt # or cd /source/ && touch 1.txt 2.txt
mkdir destination
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#! /bin/bash
SOURCE="/home/ubuntu/source"
DESTINATION="/home/ubuntu/destination"
DATE=$(date +%Y-%m-%d_%H-%M-%S)

#Create backup directory and copy files
mkdir -p $DESTINATION/$DATE
cp -r $SOURCE $DESTINATION/$DATE
echo "Backup completed on $DATE"

*or*
cp -r "$SOURCE" "$DESTINATION/$DATE" && echo "Backup succeeded on $DATE" || echo "Backup failed on $DATE" >&2
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sudo chmod +x backup.sh
./backup.sh
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Explanation
• SOURCE: The directory to be backed up.
• DESTINATION: The directory where the backup will be stored.
• DATE: Captures the current date and time to create a unique backup folder.
• mkdir -p $DESTINATION/$DATE: Creates the backup directory if it does not exist.
• cp -r $SOURCE $DESTINATION/$DATE: Copies the contents of the source directory
to the backup directory.
• echo "Backup completed on $DATE": Outputs a message indicating the completion
of the backup.

Scheduling with Cron 

To run the backup script at regular intervals, use crontab -e to edit the crontab file
and add:
* * * * * /path/to/backup_script.sh 
This example runs the script every minute. Adjust the schedule as needed.

Remove or Disable the Cron Job
crontab -e
Method 1. Delete the line containing your backup script and save

Method 2. # * * * * * /path/to/backup_script.sh # add # and save

Method 3. crontab -r # Delete your entire crontab

Method 4: Stop the Cron Service
        sudo systemctl stop cron    # Ubuntu/Debian
        sudo systemctl stop crond  # CentOS/RHEL
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2. Disk Usage Check Script 

#!/bin/bash
THRESHOLD=80
# Check disk usage and print a warning if usage is above the threshold
df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' |
while read output;
do
usage=$(echo $output | awk '{ print $1}' | cut -d'%' -f1)
partition=$(echo $output | awk '{ print $2 }')
if [ $usage -ge $THRESHOLD ]; then
echo "Warning: Disk usage on $partition is at ${usage}%"
fi
done
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Explanation
• THRESHOLD: Sets the disk usage percentage threshold.
• df -H: Lists disk usage in human-readable format.
• grep -vE '^Filesystem|tmpfs|cdrom': Filters out unnecessary lines.
• awk '{ print $5 " " $1 }': Extracts the usage percentage and partition name.
• while read output: Iterates over each line of the filtered output.
• usage=$(echo $output | awk '{ print $1}' | cut -d'%' -f1): Extracts the usage
percentage.
• partition=$(echo $output | awk '{ print $2 }'): Extracts the partition name.
• if [ $usage -ge $THRESHOLD ]; then: Checks if the usage exceeds the threshold.
• echo "Warning: Disk usage on 𝑝𝑎𝑟𝑡𝑖𝑡𝑖𝑜𝑛𝑖𝑠𝑎𝑡{usage}%": Prints a warning message

3. Service Health Check Script 

#!/bin/bash
SERVICE="nginx"
# Check if the service is running, if not, start it
if systemctl is-active --quiet $SERVICE; then
echo "$SERVICE is running"
else
echo "$SERVICE is not running"
systemctl start $SERVICE
fi
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Explanation
• SERVICE: The name of the service to check.
• systemctl is-active --quiet $SERVICE: Checks if the service is running.
• echo "$SERVICE is running": Prints a message if the service is running.
• systemctl start $SERVICE: Starts the service if it is not running.

sudo apt install nginx
sudo systemctl status nginx
./service-health.sh
sudo systemctl stop nginx
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4. Network Connectivity Check Script

touch output.txt

#!/bin/bash
HOST="google.com"
# Output file
OUTPUT_FILE="/home/ubuntu/output.txt"
# Check if the host is reachable
if ping -c 1 $HOST &> /dev/null
then
echo "$HOST is reachable" >> $OUTPUT_FILE
else
echo "$HOST is not reachable" >> $OUTPUT_FILE
fi
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Explanation
• HOST: The hostname to check.
• OUTPUT_FILE: The file to write the output to.
• ping -c 1 $HOST &> /dev/null: Pings the host once, suppressing output.
• echo "$HOST is reachable" >> $OUTPUT_FILE: Writes to the output file if the host
is reachable.• echo "$HOST is not reachable" >> $OUTPUT_FILE: Writes to the output file if the
host is not reachable.

5. Database Backup Script

Installation 

Install MySQL:
sudo apt install mysql-server -y

Set up MySQL password:
sudo mysql -u root

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY
'root';
FLUSH PRIVILEGES;
> show databases;
create database mydatabase;
exit

mkdir /home/ubuntu/db_backup #  for this /path/to/backup
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Method 1. 

#!/bin/bash
DB_NAME="mydatabase"
BACKUP_DIR="/path/to/backup"
DATE=$(date +%Y-%m-%d_%H-%M-%S)

# Perform a database backup and save it to the backup directory
mysqldump -u root -p $DB_NAME > $BACKUP_DIR/$DB_NAME-$DATE.sql
echo "Database backup completed: $BACKUP_DIR/$DB_NAME-$DATE.sql"
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Method 2. auto fill password 

#!/bin/bash
DB_NAME="mydatabase"
BACKUP_DIR="/path/to/backup"
DATE=$(date +%Y-%m-%d_%H-%M-%S)
DB_PASSWORD="root"  # Added password variable

# Perform the backup (password provided automatically)
mysqldump -u root -p"$DB_PASSWORD" "$DB_NAME" > "$BACKUP_DIR/$DB_NAME-$DATE.sql"
echo "Database backup completed: $BACKUP_DIR/$DB_NAME-$DATE.sql"
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method 3. For production and Security :

vim ~/.my.cnf
chmod 600 ~/.my.cnf

[mysqldump]
user=root
password=yourpassword
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#!/bin/bash
DB_NAME="mydatabase"
BACKUP_DIR="/path/to/backup"
DATE=$(date +%Y-%m-%d_%H-%M-%S)

mysqldump "$DB_NAME" > "$BACKUP_DIR/$DB_NAME-$DATE.sql"
echo "Backup completed: $BACKUP_DIR/$DB_NAME-$DATE.sql"
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6. System Uptime Check Script 

#!/bin/bash
# Print the system uptime
uptime -p
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Explanation
• uptime -p: Prints the system uptime in a human-readable format.

7. Listening Ports Script

Installation

Install net-tools:

sudo apt install net-tools
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#!/bin/bash
# List all listening ports and the associated services
netstat -tuln | grep LISTEN
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Explanation
• netstat -tuln: Lists all TCP and UDP listening ports.
• grep LISTEN: Filters the output to show only listening ports.
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8. Automatic Package Updates Script 

#!/bin/bash
# Update system packages and clean up unnecessary packages
sudo apt-get update && sudo apt-get upgrade -y && sudo apt-get autoremove -y && sudo apt-get clean
echo "System packages updated and cleaned up"
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Explanation
• apt-get update: Updates the package list.
• apt-get upgrade -y: Upgrades all installed packages.
• apt-get autoremove -y: Removes unnecessary packages.
• apt-get clean: Cleans up the package cache.
• echo "System packages updated and cleaned up": Outputs a message indicating
the completion of the update and cleanup.

9. HTTP Response Times Script 

#!/bin/bash
URLS=("https://www.google.com/" "https://www.linkedin.com/")
# Check HTTP response times for multiple URLs
for URL in "${URLS[@]}"; do
RESPONSE_TIME=$(curl -o /dev/null -s -w '%{time_total}\n' $URL)
echo "Response time for $URL: $RESPONSE_TIME seconds"
done
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Explanation
• URLS: An array of URLs to check.
• for URL in "${URLS[@]}": Iterates over each URL.
• curl -o /dev/null -s -w '%{time_total}\n' $URL: Uses curl to fetch the URL and
measure the total response time.
• echo "Response time for $URL: $RESPONSE_TIME seconds": Prints the response
time for each URL.

10. Monitor System Processes and Memory Usage Script 

#!/bin/bash
# Monitor system processes and their memory usage
ps aux --sort=-%mem | head -n 10
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Explanation
• ps aux: Lists all running processes.
• --sort=-%mem: Sorts the processes by memory usage in descending order.
• head -n 10: Displays the top 10 processes by memory usage.

11. System Monitoring Script: 

#!/bin/bash

threshold=90

# Monitor CPU usage and trigger alert if threshold exceeded
# Method 1: Using vmstat (most reliable)
cpu_usage=$(vmstat 1 2 | tail -1 | awk '{print 100-$15}' | cut -d. -f1)

# Alternative method using top (if vmstat doesn't work)
# cpu_usage=$(top -bn1 | grep -i "cpu(s)" | awk '{gsub(/%us,|%user,|%/, ""); for(i=1;i<=NF;i++) if($i ~ /^[0-9]+\.?[0-9]*$/) {print $i; exit}}')

# Debug: Show what we captured
echo "Current CPU usage: $cpu_usage%"

if [ ! -z "$cpu_usage" ] && [ "$cpu_usage" -gt "$threshold" ]; then
    echo "HIGH CPU ALERT: Usage is $cpu_usage% (threshold: $threshold%)"
    # Add alert/notification logic here
    # Example: mail -s "High CPU Alert" admin@example.com < /dev/null
    # Example: logger "High CPU usage detected: $cpu_usage%"
else
    echo "CPU usage normal: $cpu_usage%"
fi
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