Docker is a container runtime environment that allows programs to operate in a jailed environment without any required external dependencies. Containers are similar in some concepts to virtual machines, however, they do not use a hypervisor and run in a single kernel instance, often sharing the instance with other containers. One of the prime features of containerization is the lack of external dependencies; the container has all of the runtime libraries and components needed to run the … [Read more...] about How to Create a MySQL Docker Container for Testing
Unable to run NGINX Docker due to “13: Permission denied”
The Problem The NGINX docker container was started using the below command: # docker run --detach --name nginx_server nginx 4ffbcd5ee796b8cce3f2c6ed4cce8927d2b13a040af07b36f7a866b2157290e8 But user failed to get connection to the NGINX server. Upon troubleshooting user found below error logs: # tail -f /var/log/audit/audit.log type=AVC msg=audit(1565283160.116:316): avc: denied { write } for pid=2387 comm="nginx" name="nginx" dev="dm-0" ino=140648937 … [Read more...] about Unable to run NGINX Docker due to “13: Permission denied”
How to extract RAR files in CentOS/RHEL 7 and 8
There is no default utility in CentOS/RHEL 7 systems to extract a .rar file. This post outlines the steps to install the unar package and use of unar command to extract files with .rar extension. 1. Log in as a root user (or use sudo) and configure the latest EPEL repositories to be able to install the unar package: # yum install epel-release Note: I recommend to disable all the existing repositories and just enable the EPEL repository if you do not want to face any conflict. 2, Now … [Read more...] about How to extract RAR files in CentOS/RHEL 7 and 8
How to Disable os-prober in CentOS/RHEL 7
What is os-prober The os-prober package detects all operating systems available on the machine and returns the results in a generic machine-readable format. Sometimes os-prober may cause problems when probing some special disks (Ex: Oracle ASM disks). This post describes how to disable os-prober. Disabling os-prober os-prober is invoked by the command grub2-mkconfig when generating a new GRUB configuration file. Running grub update on a busy Oracle ASM LUNS with OS probe results in timeouts … [Read more...] about How to Disable os-prober in CentOS/RHEL 7
Understanding MySQL Storage Engines – MyISAM, MEMORY, BLACKHOLE and ARCHIVE
MyISAM Storage Engine MyISAM was the default MySQL storage engine prior to the MySQL server version 5.5.5. The current default is the InnoDB storage engine. The mysql database contains tables in the MyISAM format. Each MyISAM table is represented by three files: Formatfile: Stores the definition of the table structure (mytable.frm) Data file: Stores the contents of table rows (mytable.MYD) Index file: Stores any indexes on the table (mytable.MYI) The MyISAM storage engine … [Read more...] about Understanding MySQL Storage Engines – MyISAM, MEMORY, BLACKHOLE and ARCHIVE
Multi-Versioning in MySQL Database
MySQL database keeps the information about old versions of changed rows and supports transactional features such as concurrency and rollback. A rollback segment is an InnoDB storage area that contains the undo log. InnoDB can respond to queries for multiple versions of the same row when those queries are part of transactions that started at different times. It uses part of the undo log, the update undo buffer, to build earlier versions of database rows. Three hidden fields exist on every row … [Read more...] about Multi-Versioning in MySQL Database
How to use foreign keys to attain referential integrity in MySQL
Referential Integrity Referential integrity means that relationships between tables are consistent. MySQL enforces referential integrity by using foreign key constraints. When one table (the child table) has a foreign key to another table (the parent table), MySQL prevents you from adding a record to the child table if there is no corresponding record in the parent table. It also facilitates cascading updates and deletes to ensure that changes made to the child table are reflected in the parent … [Read more...] about How to use foreign keys to attain referential integrity in MySQL
Beginners Guide to Storage Engines in MySQL
Storage Engines and MySQL When you create a table, MySQL uses the InnoDB storage engine to create the storage for that table on the hard disk. You can choose an alternative storage engine to use for each table. Typically, you make this choice according to which storage engine offers features that best fit the needs of your application. Each storage engine has a particular set of operational characteristics. These characteristics include the types of locks that are used to manage query … [Read more...] about Beginners Guide to Storage Engines in MySQL
How to obtain MySQL metadata (metadata access methods)
A database is a structured collection of data. Metadata is "data about data". Using the following methods, MySQL provides access to metadata for databases, tables, and other objects managed by the database server: 1. INFORMATION_SCHEMA: The MySQL server contains a data dictionary implemented as a database (schema) named INFORMATION_SCHEMAthat includes a number of objects that appear to be tables. 2. SHOW statements: Proprietary syntax to obtain data on server statistics, schemas, and … [Read more...] about How to obtain MySQL metadata (metadata access methods)
“Access denied for user ‘username’@’hostname’ (using password: YES)” – Error while connecting MySQL with PHP
The Problem If the MySQL password contains a dollar sign character '$', PHP is unable to connect and issues an error like: Access denied for user 'username'@'hostname' (using password: YES) Connections via other clients work correctly. The Solution PHP interprets dollar signs inside of double quotes as starting a variable name, which will be expanded. This expansion will change the password sent to MySQL. There are 3 ways to avoid this problem: Escape the character with a … [Read more...] about “Access denied for user ‘username’@’hostname’ (using password: YES)” – Error while connecting MySQL with PHP