DEV Community: Gur

How to Find a File in Linux Using Find Command

Gur — Sat, 07 Jun 2025 07:11:38 +0000

The find command in Linux is used to search for files and directories based on name, type, size, date, or other conditions. It scans the specified directory and its sub directories to locate files matching the given criteria.
find command uses are:
• Search based on modification time (e.g., files edited last week).
• Locate files with specific permissions or content.
• Automate tasks like deleting or executing commands on found files.

Syntax of find Command in Linux
find [path...] [option] [expression] find . -name filename
• Path: Where to start searching (e.g., ~/Documents).
• Options: Refine your search (e.g., -type for files/directories).
• Expression: Criteria like filenames or sizes.

case 1. how to search based on their size

M for mb
k for kb
G for gb
c for byte

find /path/ -size 50M

case 2. how to find only file or only directory in a given path?

f for files
d for directory
l for symbolic link
b for block device
s for socket

    find /path -type f

case 3. how to search a file based on it's name

        find /path -name <dilename> # exect name mention

case 4. how to ignore upper & lower case in file name while searching files ?

         find /path -iname <filename>

Case 5. How to search files for a given user only ?

find /path –user <username>

Case 6. How to search a file based on the inode number ?

find /path inum <inode_no._of_file>
    ls -li # check inode number

Case 7. How to search a based on the no. of links?

    find /path -links <no._of_link>

Case 8. How to search a based on their permission

find /path -perm /u=r
    find /path -perm 777

Case 9. How to search all the files which start with letter a?

    find /path -iname  “a*”

Case 10. How to search all the files which are modified/created after last.txt file?

    find /path -newer last.txt

Case 11. How to search all the empty files in a given directory?

    find /path -empty

Case 12. How to search all the empty files in a given directory and at the same time delete them?

    find /path -empty -exec rm {} \;

Case 13. How to search all the files whose size are between 1-50MB ?

    find /path  -size +1M -size -50M

Case 14. How to search 15 days old files

    find /path -mtime 15

Shell Scripting useful for Production

Gur — Sun, 25 May 2025 15:20:33 +0000

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:

Automation — Runs commands without manual input.
Batch Processing — Executes multiple commands sequentially.
Scripting Language — Supports variables, loops, and conditionals.
Reusability — Scripts can be saved and reused.
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

#! /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

sudo chmod +x backup.sh
./backup.sh

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

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

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

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

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

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

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"

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"

method 3. For production and Security :

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

[mysqldump]
user=root
password=yourpassword

#!/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"

6. System Uptime Check Script

#!/bin/bash
# Print the system uptime
uptime -p

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

#!/bin/bash
# List all listening ports and the associated services
netstat -tuln | grep LISTEN

Explanation
• netstat -tuln: Lists all TCP and UDP listening ports.
• grep LISTEN: Filters the output to show only listening ports.

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"

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

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

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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