The Geek Diary

Beginners Guide to Tuning Profiles in CentOS/RHEL

Mon, 26 Oct 2020 09:01:15 GMT

Tuning Systems System administrators can optimize the performance of a system by adjusting various device settings based on a variety of use case workloads. The tuned daemon applies tuning adjustments both statically and dynamically, using tuning profiles that reflect particular workload requirements. Configuring Static Tuning The tuned daemon applies system settings when the service starts […]

How to use ansible-config to discover and investigate configuration options

Fri, 23 Oct 2020 12:08:40 GMT

Viewing Configuration Options If you want to find out what options are available in the configuration file, use the ansible-config list command. It will display an exhaustive list of the available configuration options and their default settings. This list may vary depending on the version of Ansible that you have installed and whether you have […]

How to write multiple plays and per-play privilege escalation in Ansible

Thu, 15 Oct 2020 13:10:09 GMT

Writing Multiple Plays A playbook is a YAML file containing a list of one or more plays. Remember that a single play is an ordered list of tasks to execute against hosts selected from the inventory. Therefore, if a playbook contains multiple plays, each play may apply its tasks to a separate set of hosts. […]

How to Write Ansible Playbook and run it using the ansible-playbook command

Wed, 14 Oct 2020 13:36:41 GMT

Ansible Playbooks and Ad Hoc Commands Ad hoc commands can run a single, simple task against a set of targeted hosts as a one-time command. The real power of Ansible, however, is in learning how to use playbooks to run multiple, complex tasks against a set of targeted hosts in an easily repeatable manner. A […]

How to Run Ad-Hoc Commands Using Ansible

Wed, 14 Oct 2020 12:11:08 GMT

In this post, we will learn how to run a single Ansible automation task using an ad hoc command and explain some use cases for ad hoc commands. Running ad hoc Commands with Ansible An ad hoc command is a way of executing a single Ansible task quickly, one that you do not need to […]

Beginners Guide to Managing Package Module Streams in CentOS/RHEL 8

Mon, 12 Oct 2020 16:43:27 GMT

Introduction to Application Streams CentOS/RHEL 8.0 introduces the concept of Application Streams. Multiple versions of user-space components shipped with the distribution are now delivered at the same time. They may be updated more frequently than the core operating system packages. This provides you with greater ﬂexibility to customize Red Hat Enterprise Linux without impacting the underlying stability of […]

Common Error Messages from Command xfs_repair in Linux

Fri, 02 Oct 2020 18:30:56 GMT

The post explains some of the common error messages from command xfs_repair and the repairs that it performs. disconnected inode 242002, moving to lost+found xfs_repair found an inode that is in use but is not connected to the filesystem. The inode is moved to the filesystem’s lost+found directory. Its name is its inode number (in […]

How to Permanently set the ethtool settings in CentOS/RHEL 6

Fri, 02 Oct 2020 05:02:59 GMT

Modifications made with the ethtool command are by default disappeared after a reboot. For permanent settings, the interface configuration file has to be edited. For each network device, there will be a file in the /etc/sysconfig/network-scripts/ For example, for device eth0 there will be /etc/sysconfig/network-scripts/ifcfg-eth0 containing the properties of the device. A line can be […]

How to Check if any of the RPM files were tempered with

Fri, 02 Oct 2020 03:14:32 GMT

Question: In some scenarios which it is suspected that the files in the system from an rpm installation, have been altered, changed, or tampered. For example, the system was hacked and a binary file of ssh tampered. How to check if changes were made on it comparing since installation? To verify and check if the […]

How to Create a MySQL Docker Container for Testing

Fri, 18 Sep 2020 03:28:46 GMT

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 […]

Unable to run NGINX Docker due to "13: Permission denied”

Fri, 11 Sep 2020 15:26:51 GMT

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 scontext=system_u:system_r:container_t:s0:c345,c550 […]

How to extract RAR files in CentOS/RHEL 7 and 8

Sun, 23 Aug 2020 12:57:58 GMT

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 […]

How to Disable os-prober in CentOS/RHEL 7

Sun, 23 Aug 2020 12:45:16 GMT

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 […]

Understanding MySQL Storage Engines – MyISAM, MEMORY, BLACKHOLE and ARCHIVE

Wed, 12 Aug 2020 03:16:10 GMT

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 […]

Multi-Versioning in MySQL Database

Wed, 12 Aug 2020 02:14:20 GMT

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 […]

How to use foreign keys to attain referential integrity in MySQL

Tue, 11 Aug 2020 17:01:09 GMT

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 […]

Beginners Guide to Storage Engines in MySQL

Tue, 11 Aug 2020 16:43:32 GMT

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 […]

How to obtain MySQL metadata (metadata access methods)

Sun, 09 Aug 2020 20:16:25 GMT

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 […]

"Access denied for user ‘username’@’hostname’ (using password: YES)”– Error ...

Thu, 30 Jul 2020 01:29:15 GMT

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. […]

How to Restrict MySQL User Creation with Blank Password

Thu, 30 Jul 2020 01:18:12 GMT

Question: How can we not allow user creation with a blank password in MySQL? Using a blank password for a user is always a no go. In order to restrict user creation with blank password follow the steps given below: Before MySQL 5.6 In case of MySQL version below 5.6, this can not be achieved […]