Manage KVM guest virtual machines via virsh commands

This article will guide you on how to use to manage KVM guest virtual #machines using virsh #commands.

virsh is a command line utility for managing virsh guest domains/virtual machines and the #hypervisor.

Linux list a KVM vm guest using #virsh command.

The main command interface used to control both Solaris xVM and guest domains is the virsh command. virsh provides a generic and stable interface for controlling virtualized operating systems.

Many virsh commands act asynchronously. This means that the system prompt can return before the operation has completed.

#KVM lets you turn Linux into a hypervisor that allows a host machine to run multiple, isolated virtual environments called guests or virtual machines (VMs).

To log into VM with Virsh, simply:

1. Open a shell prompt or login using ssh. 

2. Login to a host server called server1. 

3. Use the virsh console command to log in to a running VM called 'centos7' type: virsh console centos7.

The virsh destroy #command initiates an immediate ungraceful shutdown and stops the specified guest virtual machine. 

Using virsh destroy can corrupt guest virtual machine file systems. 

Use the virsh destroy command only when the guest virtual machine is unresponsive.

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DEBIAN_FRONTEND noninteractive in Docker

This article will guide you on why you should not set the DEBIAN_FRONTEND value to noninteractive is a 'cosmetic' change. If you really need to change its setting, make sure to change it back to its default value afterward. Simply prepending an apt command with DEBIAN_FRONTEND=something does not persist after the single command to which it is applied. 

apt-get update downloads the package lists from the repositories and "updates" them to get information on the newest versions of packages and their dependencies. 

It will do this for all repositories and PPAs.

To Preserve Configuration Files:

During package installation or upgrade, Debian may wish to prompt the user on overwriting a configuration file. 

This preference can be appended to the installation command:

apt-get install -q -y \
-o Dpkg::Options::="--force-confdef" \
-o Dpkg::Options::="--force-confold" \
postfix

This command will instruct the installer to quiet any messages, assume yes, and then upgrade configuration files if no changes are present in the new package.

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Roundcube empty startup greeting

This article will guide you on methods to resolve #Roundcube empty startup greeting error which occurs due to many reasons which include improper configuration of SSL, network #problem, firewall #error and so on.

Roundcube is a webmail client with strong security features and extensive customization options from its plugin repository.

It is important to set Roundcube config file as follows:

$config['default_host'] = 'imaps://domain.tld';

// TCP port used for IMAP connections

$config['default_port'] = 993;


To fix cPanel Roundcube Webmail "An error occurred":

This error indicates a potentially corrupt index file. 

1. establish an SSH session with the server and navigate to:

/home/<username>/mail/<domain name>/<email account name>/

2. Find dovecot.index and rename it to dovecot.index.bak.

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AWS security vulnerabilities

This article will guide you on how to create a virtual machine using #Lightsail in AWS.

AWS Cloud Compliance enables you to understand the robust controls in place at AWS to maintain security and data protection in the cloud. 

The IT infrastructure that AWS provides to its customers is designed and managed in alignment with best #security practices and a variety of IT security standards.

AWS WAF is a web application #firewall that helps protect your web applications or APIs against common web exploits that may affect availability, compromise security, or consume excessive resources.

List of AWS Limitations:

1. #AWS service limits. AWS service limits are set by the platform.

2. Technology limitations. An exceptional characteristic of this limiting factor is that it can be applied to all Cloud services, not just on AWS.

3. Lack of relevant knowledge by your team.

4. Technical support fee.

5. General Cloud Computing issues.

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Vue js authentication using vue-router

This article will guide you on how to set up Vue.js authentication using vue-router. If we couple Vue.js with vue-router, we can build high-performance applications.

To run a Vue application:

1. Open the package.json file and add the following:

[...]
"scripts": {
    "dev": "webpack-dev-server --inline --progress --config build/webpack.dev.conf.js",
    "start": "npm run dev",
    "server": "node server/app",
    "build": "node build/build.js"
  },
[...]

2. We added the server script to help us start up the node server. Now, run the following command to start the server:

npm run server

3. Then create another terminal instance and run the Vue app like this:

npm run dev

This will build all the assets and start the application. You can open the link it shows you to see the application.

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Troubleshoot Redis latency Issues

This article will guide you on steps to troubleshoot Redis #latency problems.

#Amazon #ElastiCache allows you to seamlessly set up, run, and scale popular open-source compatible in-memory data stores in the cloud. 

Build data-intensive apps or boost the performance of your existing databases by retrieving data from high throughput and low latency in-memory data stores.

#Redis #performance monitoring metrics:

1. Used Memory

"memory_used" gives the total amount of memory in bytes that is used by the Redis server. If it exceeds physical memory, system will start swapping causing severe performance degradation.

2. Peak used memory

"memory_used_peak" metric calculates and displays the highest amount of memory in bytes consumed by the Redis server.

3. Used CPU system

The metric "cpu_used_sys" gets the total amount of system CPU consumed by the Redis server. High CPU usage is not bad as long as it doesn't exceed CPU limit.

4. Used CPU user

The metric "cpu_used_user" records the total amount of user CPU consumed by the Redis server.

5. Used CPU user children

The metric "cpu_used_user_children" records the total amount of user CPU consumed by other background processes.

6. Used CPU system children

Get the total amount of system #CPU consumed by background processes with the metric "cpu_used_sys_children".

7. Rejected connections

Use the metric "total_conn_rec" and get the total number of connections accepted by the Redis server.

8. Connected clients

Get the total number of slave connections made to the Redis server with the metric "conn_slaves".

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