MySQL Backup & Restore

Backups

Full Backups

A full backup captures the entire database at a specific point in time. It includes all the data, schema, and configurations necessary to restore the database to that state. Full backups serve as the foundation for PITR and are typically performed periodically (e.g., daily or weekly) to ensure that there is a recent baseline from which to start the recovery process.

Incremental Backups

Incremental backups capture only the changes made to the database since the last backup (full or incremental). This approach reduces the amount of data that needs to be backed up, saving time and storage space. In MySQL, binary logs are crucial for incremental backups as they record all database changes.

Binary Logs

Binary logs in MySQL are essential for PITR. They record all database changes (e.g., INSERT, UPDATE, DELETE statements) in a binary format. These logs enable the replay of changes during recovery, allowing you to restore the database to any specific point in time by applying the changes recorded after the last full backup.

How Binary Logs Work

1. Enable Binary Logging: Binary logging must be enabled on the MySQL server. This can be done by adding the log_bin directive to the MySQL configuration file (my.cnf) and restarting the MySQL server.

2. Recording Changes: Once binary logging is enabled, MySQL starts recording all changes to the database in binary log files. Each log file is given a sequential number (e.g., mysql-bin.000001, mysql-bin.000002).

3. Managing Log Files: As the number of binary log files increases, it’s important to manage them to prevent disk space issues. MySQL provides options to purge old binary logs that are no longer needed.

4. Point-in-Time Recovery: To perform a point-in-time recovery, you first restore the database from the most recent full backup. Then, you apply the changes recorded in the binary logs to bring the database to the desired state.

Point-in-Time B&R

PITR relies on both full backups and incremental backups to provide a comprehensive recovery solution. These two types of backups work together to ensure that you can restore your database to any specific point in time.

Significance of (PITR)

Point-in-Time Recovery (PITR) allows you to restore a database to a specific moment, often before an error or data corruption occurred. This capability is critical for minimizing data loss and maintaining data integrity, especially in environments where continuous availability and data accuracy are paramount.

  • PITR involves a combination of full backups and incremental backups (or binary logs in MySQL), enabling administrators to revert the database to any desired point in time.
  • This method provides flexibility and precision in recovery operations, ensuring that only the necessary data changes are applied during the restoration process.

PITR - Example 1

Let us explore a scenario where you are tasked with taking a point in time backup of the MySQL server that houses a database named world. Within this database, you will encounter tables like cities, countries and languages, each holding data related to cities, countries and languages spoken worldwide.This exercise will build upon the world database created in the previous exercise: Backup and Restore Using MySQL.

  • Say you have a full logical backup of your whole database in your last mysqldump file as of yesterday evening. However, several changes may have been made (including data loss) since then.
  • Using point-in-time backup and restore, you can get each and every change that occurred since then, so that even after your last logical backup you have a record of all new transactions.
  • Point-in-time backup is the set of binary log files generated subsequent to a logical backup operation of a database. The binary log files contain events that describe database changes such as table creation operations or changes to table data.
  • To restore a database to a point-in-time, you will be using binary log files containing changes of a database for a time interval along with the last logical backup of the database.

To install MySQL go to Data/MySQL page

Data

The World database used in this lab comes from the following source: https://dev.mysql.com/doc/world-setup/en/ 

Linux in WSL

Since I’ll be using Linux in WSL I’ll have an extra word or two in addition to the usual linux commands to access my local directory

~$ cd /mnt/d/data/Linux_projects/Final_projects/C7

Download Scripts

Download the required SQL script file in the linux terminal by executing the command below to save all the scripts to our local machine:

  • I created a directory for the files first
  • Downloaded 3 back to back
$ wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0231EN-SkillsNetwork/datasets/World/world_mysql_script.sql -P C7

$ wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0231EN-SkillsNetwork/datasets/World/world_mysql_update_A.sql -P C7

$ wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0231EN-SkillsNetwork/datasets/World/world_mysql_update_B.sql -P C7

# OUTPUT
--2012-09-30 17:18:20--  https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0231EN-SkillsNetwork/datasets/World/world_mysql_update_B.sql
Resolving cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud (cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud)... 198.23.119.245
Connecting to cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud (cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud)|198.23.119.245|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 3497 (3.4K) [application/x-sql]
Saving to: ‘C7/world_mysql_update_B.sql’

Verify Download

~$ ls
world_mysql_script.sql  world_mysql_update_A.sql  world_mysql_update_B.sql

Start MySQL

$ sudo systemctl start mysql

Login to MySQL

$:/mnt/d/data/Linux_projects/Final_projects/C7$ sudo mysql -u root -p
Enter password:

# RESPONSE
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.39-0ubuntu0.22.04.1 (Ubuntu)

Copyright (c) 2000, 2024, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

Create db

Use db

Execute first Script file

  • To create the first db from the backup script file world_mysql_script.sql
  • run the last line of code
  • It will take a few seconds to complete the creation of the db
mysql>create database world;
mysql>use world;
mysql>source world_mysql_script.sql;

Show Dbs

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| world              |
+--------------------+
5 rows in set (0.13 sec)

Show Tables

mysql> SHOW TABLES;
+-----------------+
| Tables_in_world |
+-----------------+
| city            |
| country         |
| countrylanguage |
+-----------------+
3 rows in set (0.01 sec)

View all records for CAN

mysql> SELECT * FROM city WHERE countrycode='CAN';
Empty set (0.00 sec)

Restore Again

  • As you see it appears that the first restore using the first script didn’t cover the data that was added later
  • If you remember this could be the intermittent backup which is information added since the complete backup
  • So let’s ALTER the db by executing the second script file
mysql> source world_mysql_update_A.sql;
Query OK, 0 rows affected (0.00 sec)

Query OK, 1 row affected (0.00 sec)

Query OK, 1 row affected (0.01 sec)....

# View all records again
mysql> SELECT * FROM countrylanguage WHERE countrycode='CAN';
# we see that the languages were added (I guess I should've run the same code before as well, but take my word for it this data was not there)

Close Connection

mysql> \q
Bye
~:/mnt/d/data/Linux_projects/Final_projects/C7$

Dump Full Backup

Stop MySQL

Before you backup you must STOP MySQL

sudo systemctl stop mysql

Full Logical Backup

Next, create a full logical backup of the current state of your whole world database.

  • Use the command below in the terminal
  • Redirect the output to > filename
sudo mysqldump --user=root --password --flush-logs --delete-master-logs --databases world > world_mysql_full_backup.sql
[sudo] password for yashaya:cccc

# File is created and saved

# For in the cloud use I had to run this code to backup the countrylanguage TABLE ONLY of the world db
mysqldump --host=mysql --port=3306 --user=root --password world countrylanguage > world_countrylanguage_mysql_backup.sql

View Content of Backup file

If you want to inspect the content of the file for informational purposes use

cat world_countrylanguage_mysql_backup.sql

Login to MySQL

~$ sudo mysql -u root -p
Enter password:
        
# RESPONSE        
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 10
Server version: 8.0.39-0ubuntu0.22.04.1 (Ubuntu)

Copyright (c) 2000, 2024, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

Repeat Steps above

mysql> SHOW TABLES;
+-----------------+
| Tables_in_world |
+-----------------+
| city            |
| country         |
| countrylanguage |
+-----------------+
3 rows in set (0.00 sec)

# Review data for CAN
mysql> SELECT * FROM city WHERE countrycode='CAN';
Empty set (0.00 sec)     # An empty set again

Intermittent Backup

Restore from Intermittent

  • Let’s pretend the last script: ~update_B.sql is an intermittent backup since the dump was created
  • Run the script for it
mysql> source world_mysql_update_B.sql;

# Review data for CAN
mysql> SELECT * FROM city WHERE countrycode='CAN';
+------+------------------+-------------+------------------+------------+
| ID   | Name             | CountryCode | District         | Population |
+------+------------------+-------------+------------------+------------+
| 1810 | Montréal         | CAN         | Québec           |    1016376 |
| 1811 | Calgary          | CAN         | Alberta          |     768082 |
| 1812 | Toronto          | CAN         | Ontario          |     688275 |
| 1813 | North York       | CAN         | Ontario          |     622632 |
| 1814 | Winnipeg         | CAN         | Manitoba         |     618477 |
| 1815 | Edmonton         | CAN         | Alberta          |     616306 |
| 1816 | Mississauga      | CAN         | Ontario          |     608072 |
| 1817 | Scarborough      | CAN         | Ontario          |     594501 |
| 1818 | Vancouver        | CAN         | British Colombia |     514008 |
| 1819 | Etobicoke        | CAN         | Ontario          |     348845 |
| 1820 | London           | CAN         | Ontario          |     339917 |
| 1821 | Hamilton         | CAN         | Ontario          |     335614 |
| 1822 | Ottawa           | CAN         | Ontario          |     335277 |
| 1823 | Laval            | CAN         | Québec           |     330393 |
| 1824 | Surrey           | CAN         | British Colombia |     304477 |
| 1825 | Brampton         | CAN         | Ontario          |     296711 |
| 1826 | Windsor          | CAN         | Ontario          |     207588 |
| 1827 | Saskatoon        | CAN         | Saskatchewan     |     193647 |
| 1828 | Kitchener        | CAN         | Ontario          |     189959 |
| 1829 | Markham          | CAN         | Ontario          |     189098 |
| 1830 | Regina           | CAN         | Saskatchewan     |     180400 |
| 1831 | Burnaby          | CAN         | British Colombia |     179209 |
| 1832 | Québec           | CAN         | Québec           |     167264 |
| 1833 | York             | CAN         | Ontario          |     154980 |
| 1834 | Richmond         | CAN         | British Colombia |     148867 |
| 1835 | Vaughan          | CAN         | Ontario          |     147889 |
| 1836 | Burlington       | CAN         | Ontario          |     145150 |
| 1837 | Oshawa           | CAN         | Ontario          |     140173 |
| 1838 | Oakville         | CAN         | Ontario          |     139192 |
| 1839 | Saint Catharines | CAN         | Ontario          |     136216 |
| 1840 | Longueuil        | CAN         | Québec           |     127977 |
| 1841 | Richmond Hill    | CAN         | Ontario          |     116428 |
| 1842 | Thunder Bay      | CAN         | Ontario          |     115913 |
| 1843 | Nepean           | CAN         | Ontario          |     115100 |
| 1844 | Cape Breton      | CAN         | Nova Scotia      |     114733 |
| 1845 | East York        | CAN         | Ontario          |     114034 |
| 1846 | Halifax          | CAN         | Nova Scotia      |     113910 |
| 1847 | Cambridge        | CAN         | Ontario          |     109186 |
| 1848 | Gloucester       | CAN         | Ontario          |     107314 |
| 1849 | Abbotsford       | CAN         | British Colombia |     105403 |
| 1850 | Guelph           | CAN         | Ontario          |     103593 |
| 1851 | Saint John´s     | CAN         | Newfoundland     |     101936 |
| 1852 | Coquitlam        | CAN         | British Colombia |     101820 |
| 1853 | Saanich          | CAN         | British Colombia |     101388 |
| 1854 | Gatineau         | CAN         | Québec           |     100702 |
| 1855 | Delta            | CAN         | British Colombia |      95411 |
| 1856 | Sudbury          | CAN         | Ontario          |      92686 |
| 1857 | Kelowna          | CAN         | British Colombia |      89442 |
| 1858 | Barrie           | CAN         | Ontario          |      89269 |
+------+------------------+-------------+------------------+------------+
49 rows in set (0.00 sec)

Quit MySQL

mysql> \q
Bye

Simulate Crash

We’ll create a scenario where a database crash will be conducted intentionally which will result a significant loss of your world database files.

  • To simulate a database crash and create a scenario for recover stop the MySQL service
  • Remove the database files

Stop MySQL

sudo systemctl stop mysql

Here’s what each part of the command does:

  • systemctl: This is a command-line utility used to manage systemd, which is a system and service manager for Linux operating systems. It allows users to start, stop, enable, disable, and manage services and other units.

  • stop: This subcommand of systemctl instructs systemd to stop the specified service. In this case, mysql refers to the MySQL service

Remove Db

  • Remove the db so we can show how the recovery part of B & R
  • MySQL by default stores the dbs in: /var/lib/mysql/
  • The rm -rf command removes the world directory and all of its contents recursively and forcefully. This includes all the data files, subdirectories, and any other files related to the world database within the MySQL data directory.
  • After removing the dv, try to retrieve records from any table (let’s try the city table) from the database
  • Should get an error because the db no longer exists
sudo rm -rf /var/lib/mysql/world

# Verify deletion
$ sudo mysql --user=root --password --execute="SELECT * FROM world.city;"
Enter password:
        
# RESPONSE
ERROR 2013 (HY000) at line 1: Lost connection to MySQL server during query

Restore DB

Let’s show how to restore the database after we had made a backup earlier

  • So we have a backup file created in the Dump section above
  • We also have an intermittent backup the last script: ~update_B.sql which we are going to pretend was done after the full logical backup

Display Binary Logs

$ sudo mysql --user=root --password --execute="SHOW BINARY LOGS;"
Enter password:
        
+---------------+-----------+-----------+
| Log_name      | File_size | Encrypted |
+---------------+-----------+-----------+
| binlog.000004 |     15805 | No        |
| binlog.000005 |       157 | No        |
| binlog.000006 |       157 | No        |
+---------------+-----------+-----------+

Combine Binary Logs

  • Combine all binary log files together into a single file
  • Here’s what each part of the command does:

    • Read Binary Log Files: The mysqlbinlog utility reads the specified binary log files (binlog.000003 and binlog.000004).

    • Convert to SQL Statements: mysqlbinlog converts the binary format of the log files into readable SQL statements. These statements represent the database changes recorded in the logs.

    • Redirect Output: The SQL statements are redirected and saved into a file named logfile.sql.

$ sudo mysqlbinlog /var/lib/mysql/binlog.000004 /var/lib/mysql/binlog.000005  /var/lib/mysql/binlog.000006 > logfile.sql

PITR

Now we are ready to perform Point-In-Time-Recovery.

Restore Full Backup

  • First restore the full logical backup of your whole world database you created earlier in this example using the command below in the terminal
  • Enter your MySQL service session password from the MySQL service session tab if necessary
  • Note the < arrow where we are using the ~full_backup.sql file as the source
/C7$ sudo mysql --user=root --password < world_mysql_full_backup.sql
Enter password:

Verify Data

To verify if you have the updates from the update script world_mysql_update_B.sql, retrieve all the Canada (countrycode=’CAN’) related records from the city table

sudo mysql --user=root --password --execute="SELECT * FROM world.city WHERE countrycode='CAN';"

# OUTPUT
empty set

Run Logfile

We obviously took some steps after the full backup and were all tracked in the log files that were combined into one. So let’s apply the steps in the logfile to the db to fully restore it to the exact point in time

sudo mysql --user=root --password < logfile.sql

Verify Data

Now that the full backup as well as the logfile has been executed, let’s verify the output and compare it to the output above, prior to the simulated crash test.

C7$ sudo mysql --user=root --password --execute="SELECT * FROM world.city WHERE countrycode='CAN';"
Enter password:
        
+------+------------------+-------------+------------------+------------+
| ID   | Name             | CountryCode | District         | Population |
+------+------------------+-------------+------------------+------------+
| 1810 | Montréal         | CAN         | Québec           |    1016376 |
| 1811 | Calgary          | CAN         | Alberta          |     768082 |
| 1812 | Toronto          | CAN         | Ontario          |     688275 |
| 1813 | North York       | CAN         | Ontario          |     622632 |
| 1814 | Winnipeg         | CAN         | Manitoba         |     618477 |
| 1815 | Edmonton         | CAN         | Alberta          |     616306 |
| 1816 | Mississauga      | CAN         | Ontario          |     608072 |
| 1817 | Scarborough      | CAN         | Ontario          |     594501 |
| 1818 | Vancouver        | CAN         | British Colombia |     514008 |
| 1819 | Etobicoke        | CAN         | Ontario          |     348845 |
| 1820 | London           | CAN         | Ontario          |     339917 |
| 1821 | Hamilton         | CAN         | Ontario          |     335614 |
| 1822 | Ottawa           | CAN         | Ontario          |     335277 |
| 1823 | Laval            | CAN         | Québec           |     330393 |
| 1824 | Surrey           | CAN         | British Colombia |     304477 |
| 1825 | Brampton         | CAN         | Ontario          |     296711 |
| 1826 | Windsor          | CAN         | Ontario          |     207588 |
| 1827 | Saskatoon        | CAN         | Saskatchewan     |     193647 |
| 1828 | Kitchener        | CAN         | Ontario          |     189959 |
| 1829 | Markham          | CAN         | Ontario          |     189098 |
| 1830 | Regina           | CAN         | Saskatchewan     |     180400 |
| 1831 | Burnaby          | CAN         | British Colombia |     179209 |
| 1832 | Québec           | CAN         | Québec           |     167264 |
| 1833 | York             | CAN         | Ontario          |     154980 |
| 1834 | Richmond         | CAN         | British Colombia |     148867 |
| 1835 | Vaughan          | CAN         | Ontario          |     147889 |
| 1836 | Burlington       | CAN         | Ontario          |     145150 |
| 1837 | Oshawa           | CAN         | Ontario          |     140173 |
| 1838 | Oakville         | CAN         | Ontario          |     139192 |
| 1839 | Saint Catharines | CAN         | Ontario          |     136216 |
| 1840 | Longueuil        | CAN         | Québec           |     127977 |
| 1841 | Richmond Hill    | CAN         | Ontario          |     116428 |
| 1842 | Thunder Bay      | CAN         | Ontario          |     115913 |
| 1843 | Nepean           | CAN         | Ontario          |     115100 |
| 1844 | Cape Breton      | CAN         | Nova Scotia      |     114733 |
| 1845 | East York        | CAN         | Ontario          |     114034 |
| 1846 | Halifax          | CAN         | Nova Scotia      |     113910 |
| 1847 | Cambridge        | CAN         | Ontario          |     109186 |
| 1848 | Gloucester       | CAN         | Ontario          |     107314 |
| 1849 | Abbotsford       | CAN         | British Colombia |     105403 |
| 1850 | Guelph           | CAN         | Ontario          |     103593 |
| 1851 | Saint John´s     | CAN         | Newfoundland     |     101936 |
| 1852 | Coquitlam        | CAN         | British Colombia |     101820 |
| 1853 | Saanich          | CAN         | British Colombia |     101388 |
| 1854 | Gatineau         | CAN         | Québec           |     100702 |
| 1855 | Delta            | CAN         | British Colombia |      95411 |
| 1856 | Sudbury          | CAN         | Ontario          |      92686 |
| 1857 | Kelowna          | CAN         | British Colombia |      89442 |
| 1858 | Barrie           | CAN         | Ontario          |      89269 |
+------+------------------+-------------+------------------+------------+

Backup Example 2

Data

Db script is located online and can be gotten via. I already have that locally from above.

wget https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBM-DB0231EN-SkillsNetwork/datasets/World/world_mysql_script.sql

Start MySQL

Reminder: Here’s what each part of the command does:

  • sudo: This prefix grants temporary administrative privileges to the command that follows it. It allows the user to execute the subsequent command with superuser (root) privileges.
  • systemctl: This is a command-line utility used to manage systemd, which is a system and service manager for Linux operating systems. It allows users to start, stop, enable, disable, and manage services and other units.
  • start: This subcommand of systemctl instructs systemd to start the specified service. In this case, mysql refers to the MySQL service.

Login to MySQL

Here’s what each part of the command does:

  • mysql: This is the command used to launch the MySQL command-line interface.
  • -u root: This option specifies the username to use when connecting to the MySQL server. In this case, it specifies that the root user should be used.
  • -p: This option prompts the user to enter the password for the specified MySQL user (in this case, the root user). After entering the password, if it’s correct, the user gains access to the MySQL CLI with administrative privileges.
$ sudo systemctl start mysql
[sudo] password for yashaya:
        
# Login to MySQL
$ sudo mysql -u root -p
Enter password:
        
# RESPONSE
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 13
Server version: 8.0.39-0ubuntu0.22.04.1 (Ubuntu)
Copyright (c) 2000, 2024, Oracle and/or its affiliates.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

Create db

Use db

Execute Script

Execute the script to complete the creation of the db. The script holds the data for the tables: cities, countries, languages

create database world;
use world;
source world_mysql_script.sql;

List Dbs

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| world              |
+--------------------+
5 rows in set (0.13 sec)

Stop MySQL

Before executing a backup you MUST stop MySQL. Here we’ll first quit it, then stop it

# ---------- QUIT
mysql> \q
Bye

# --------- STOP
~$ sudo systemctl stop mysql

Backup

Complete backup of the db, which will recursively copy all the directories and subs to the specified > directory

Here’s what each part of the command does:

  • cp: This is the command used to copy files and directories.
  • -R: This option is used to specify a recursive copy, meaning it will copy the specified directory and all of its contents, including subdirectories and files.
  • /var/lib/mysql: MySQL data files, including databases, tables, and other related files are present in this directory.
  • Note this will copy all the data in the directory not just one database
  • /path/to/backup_directory: This is the destination directory where the MySQL data directory will be copied. You should replace “/path/to/backup_directory” with the directory which you want the backup to be stored.
sudo cp -R /var/lib/mysql /path/to/backup_directory
sudo cp -R /var/lib/mysql /mnt/d/data/Linux_projects/Final_projects/C7

Verify

$ sudo ls -l /mnt/d/data/Linux_projects/Final_projects/C7
total 5120
-rwxrwxrwx 1 yashaya yashaya  74134 Oct  1 09:10 logfile.sql
drwxrwxrwx 1 yashaya yashaya    512 Oct  1 10:33 mysql
-rwxrwxrwx 1 yashaya yashaya 241056 Sep 30 18:01 world_mysql_full_backup.sql
-rwxrwxrwx 1 yashaya yashaya 389702 Sep  6  2022 world_mysql_script.sql
-rwxrwxrwx 1 yashaya yashaya   1035 Sep  6  2022 world_mysql_update_A.sql
-rwxrwxrwx 1 yashaya yashaya   3497 Sep  6  2022 world_mysql_update_B.sql

Rename Old Directory

Now that we have a copy of the entire /mysql directory we can rename the previous one on the default path: to mysql_old

sudo mv /var/lib/mysql /var/lib/mysql_old

Copy Backup to Default

Now we can recursively copy the entire mysql directory that we backed up to /mnt/d/data/Linux_projects/Final_projects/C7 back to the default location to replace the corrupt one.

Ensure there is sufficient storage space before performing the copying

sudo cp -R /mnt/d/data/Linux_projects/Final_projects/C7/mysql /var/lib/mysql

Set Ownership of Directory

sudo chown -R mysql:mysql /var/lib/mysql

Here’s what each part of the command does:

  • chown: Stands for change ownership, a command used to change the ownership of files or directories in Linux.
  • -R: Specifies a recursive operation,including subdirectories and files.
  • mysql:mysql: Specifies the new owner and group for the directory and its contents. In this case, it sets the user to “mysql” and the group to “mysql”.
  • /var/lib/mysql: Specifies the directory whose ownership will be changed. This is typically the MySQL data directory.

Once completed you can restart the MySQL service using the command: sudo systemctl start mysql