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"SR BACKEND FAILURE 181" error - Fix it Now ?


This article covers how to fix "SR BACKEND FAILURE 181" error. Generally, user experiences issues with any storage related operations after installation or upgrade to XenServer 6.x. 

As a workaround, you can remove all special characters from the virtual machine name-label and description fields.  Contact our Technical Support to assist you in resolving the issue. 

Note: Special character should not be used for the storage repository and description field.

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Cloudflare err_ssl_protocol_error - Fix it Now ?


This article covers methods to resolve Cloudflare ERR_SSL_PROTOCOL_ERROR. Basically, this error happens as a result of a number of reasons that include wrong DNS settings, SSL mode, TLS version or issues with SSL certificate. 


To fix this error,

1. If you are not the site owner, contact the site owner and let them know you are having issues accessing their site.

2. The domain name has not fully been set to use Cloudflare yet. Check to see if there are non-Cloudflare nameservers that are conflicting with the assigned Cloudflare name servers.

3. You are signed up for Cloudflare, but you have set a DNS record to :grey:. If you have a subdomain or hostname and that serves HTTP/HTTPS traffic, we would advise that you :orange: this DNS record to take advantage of Cloudflare’s security and performance features. See What subdomains are appropriate for :orange:/:grey: clouds? 69

4. The Free Universal SSL certificate hasn’t yet been deployed, :grey: (deactivate) Cloudflare so that your website can continue to use your origin’s SSL certificate. Wait 24 hours and :orange: (activate) Cloudflare again to see if your SSL certificate has been successfully deployed.

5. You have some conflict with TLS 1.3, disable it and see if you still encounter the error.

6. You have selected Full SSL (strict) under your SSL/TLS app, but your origin does not have a valid certificate (i.e., it is expired, self-signed, or not issued by a trusted CA). Temporarily select another SSL option until you have a valid origin certificate in place.

7. Try to look at developer web console (firefox Ctrl+Shift+K) - anything interesting under Security tab.

8. Also, Try to run the command curl -vk on the affected domain.

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Cloudflare 502 error - Fix it Now ?


This article covers methods to resolve Cloudflare 502 error. Basically, the Cloudflare 502 error triggers when the origin web server responds with a standard HTTP 502 bad gateway or 504 gateway timeout error. 

This happens due to firewall restrictions and server resource issues.


Cause of 502 Bad Gateway Errors:

1. Domain name not resolvable

The domain name is not pointing to the correct IP or it does not point to any IP this problem may happen. Also, DNS propagation could take some time to make changes in DNS setting. It may take 24 to 48 hours to make reflect which is dependent upon the TTL defined per record on the DNS.

2. server down

The origin server is not reachable, this may due to the server is down for some reason or there is no communication to the server given.

3. Firewall blocks

A firewall interrupts the communication between the edge servers and the origin server. This may be caused by security plugins of your CMS.

As a part of DDOS protection and mitigation process or due to some strict firewall rules servers can be blocked from accessing the original server.

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Configure Varnish with Apache - How to do it


This article covers how to configure Varnish #cache on the #Apache server. Varnish is an HTTP accelerator and a useful tool for speeding up a server, especially during a times when there is high traffic to a site. 

It works by redirecting visitors to static pages whenever possible and only drawing on the virtual private server itself if there is a need for an active process.

#Varnish is a caching HTTP reverse proxy. It receives requests from clients and tries to answer them from the cache.


Where is varnish configuration file?

The Varnish configuration file will be located in the /etc/varnish directory in CentOS 7. 

To make Varnish work in front of Apache, you will need to set up some basic configurations. 

By default Varnish listens on port 6081 . 

You will need to change port 6081 to 80 so that website requests access the Varnish cache first.


What is varnish WordPress?

Varnish is a full-page cache and HTTP preprocessor which can be used to speed up requests for a WordPress site. 

Setting up Varnish is a technical task, as it requires installing and configuring a system package on a web server, rather than just installing a plugin.

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Install OpenCV on Ubuntu


This article will guide you on different methods to install OpenCV on #Ubuntu 20.04. Even though installing the packaged version from the Ubuntu repository is easier, building OpenCV from source gives you more flexibility, and it should be your first option when installing OpenCV.

#OpenCV is the huge open-source library for the computer vision, machine learning, and image processing and now it plays a major role in real-time operation which is very important in today's systems. 

By using it, one can process images and videos to identify objects, faces, or even handwriting of a human.


To install the latest OpenCV version from the source:

1. Install the required dependencies:

sudo apt install build-essential cmake git pkg-config libgtk-3-dev \
    libavcodec-dev libavformat-dev libswscale-dev libv4l-dev \
    libxvidcore-dev libx264-dev libjpeg-dev libpng-dev libtiff-dev \
    gfortran openexr libatlas-base-dev python3-dev python3-numpy \
    libtbb2 libtbb-dev libdc1394-22-dev

2. Clone the OpenCV’s and OpenCV contrib repositories:

mkdir ~/opencv_build && cd ~/opencv_build
git clone https://github.com/opencv/opencv.git
git clone https://github.com/opencv/opencv_contrib.git

3. Once the download is complete, create a temporary build directory, and switch to it:

cd ~/opencv_build/opencv
mkdir build && cd build

4. Set up the OpenCV build with CMake:

cmake -D CMAKE_BUILD_TYPE=RELEASE \
    -D CMAKE_INSTALL_PREFIX=/usr/local \
    -D INSTALL_C_EXAMPLES=ON \
    -D INSTALL_PYTHON_EXAMPLES=ON \
    -D OPENCV_GENERATE_PKGCONFIG=ON \
    -D OPENCV_EXTRA_MODULES_PATH=~/opencv_build/opencv_contrib/modules \
    -D BUILD_EXAMPLES=ON ..

5. Start the compilation process:

make -j8

6. Install OpenCV with:

sudo make install


To uninstall OpenCV Linux: 

i. If you installed OpenCV from package manager, it's best to remove those packages. Check: apt list --installed | grep opencv

ii. If you built it yourself, and you still got the build folder, run sudo make uninstall from the OpenCV build directory.

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Install XRDP Server


This article will guide you on steps to install XRDP #Server on #Ubuntu. To provide remote access via RDP, a Windows native protocol, XRDP behind the scenes uses #VNC, a remote access protocol more common in Linux.

After #xrdp is installed you can start the server with the following command:

Service xrdp start.

Service xrdp-sesman start (Thanks to Greg for pointing that out) — UPDATE!!

If want it to auto start after reboot you need to run this command also: update-rc.d xrdp enable (It will not start xrdp-sesman automatic).


To use XRDP Linux:

1. With #Ubuntu 18.04 first install xrdp: sudo apt-get -y install xrdp.

2. Next, one may adjust the configuration file: sudo nano /etc/xrdp/xrdp.ini.

3. Set encryption level to high: encrypt_level=high.

4. Next, allow just RDP through the local firewall: sudo ufw allow 3389/tcp.

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Install Vesta control panel in Ubuntu


This article will guide you on easy steps to install Vesta control panel in #Ubuntu. VestaCP is a control panel for Linux with many features that facilitate the administration of a #server. 

Vesta Development team provides an installer script that automates setting up of Vesta hosting control panel on Ubuntu / Debian and RHEL based Linux distributions. Login to your Ubuntu / #Debian system and ensure the system is updated. Download #Vesta installer. Run install with sudo if you're logged in as standard user.

To install vestaCP on Ubuntu:

1. # Connect to your server as root via #SSH

ssh root@your.server

2. # Download installation script

curl -O http://vestacp.com/pub/vst-install.sh

3. # Run it

bash vst-install.sh

To change my VestaCP port:

i. conf file and change the port that NGINX listens on from 8083 to 2083 (or the port you chose to use). listen 2083; 

ii. Once the port has been changed, press CTRL+X , followed by y , and then hit enter to save your changes. 

iii. The final step is removing the firewall entry for the previous port we were using.

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Microsoft SQL server error 18470 How to fix it


This article will guide you on the different factors that causes SQL server error: 18470 and also how to fix this #error.

In SQL Server Configuration Manager, in the left pane, click SQL Server Services. In the results pane, right-click SQL Server (#MSSQLServer) or a named instance, and then click Start, Stop, Pause, Resume, or Restart.

User gets the #Microsoft SQL Server Error: 18470. This may happen if the SA (System Administrator) user account is disabled in #SQL Server. It can be verified by trying to log in to SQL Server Management Studio (#SSMS) using the SA account. In the Login Properties screen, select Status on the left side.

To Microsoft SQL Server Error 18456:

1. Log In with Remote Desktop.

2. Run Microsoft SQL Server Management.

3. Checking the Server Authentication Mode.

4. Restart the SQL Service.

5. Checking SQL User Permissions.

6. Mapping the User to the #Database.

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Ansible Playbook to Install WordPress with LAMP


This article will guide you on the step to follow to use #Ansible Playbook to install #WordPress with #LAMP on #Ubuntu 18.04.

In Ansible, the role is the primary mechanism for breaking a #playbook into multiple files. This simplifies writing complex #playbooks, and it makes them easier to reuse. The breaking of playbook allows you to logically break the playbook into reusable components.

To start using Ansible:

1. Prerequisites.

2. Install Ansible.

3. Establish a manual connection to a managed node.

4. Run your first network Ansible command.

5. Create and run your first network Ansible Playbook.

6. Gathering facts from network devices.

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MySQL BLOB Data Type


This article will guide you on how #MySQL #BLOB data type works in storing and displaying images with #PHP on Ubuntu 18.04. A BLOB is a binary large object that can hold a variable amount of data.
A Binary Large OBject (BLOB) is a collection of #binary data stored as a single entity in a database management system. Blobs are typically images, audio or other multimedia objects, though sometimes binary executable code is stored as a blob.
The four BLOB types are #TINYBLOB , #BLOB , #MEDIUMBLOB , and #LONGBLOB . These differ only in the maximum length of the values they can hold. The four TEXT types are TINYTEXT , TEXT , MEDIUMTEXT , and LONGTEXT .
The size of blob in MySQL:
TINYBLOB - Up to 255 bytes - 1 byte
BLOB - Up to 64 Kb - 2 bytes
MEDIUMBLOB - Up to 16 Mb - 3 bytes
LONGBLOB - Up to 4 Gb - 1 Bytes

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List installed software Linux


This article will guide you on different methods to #list all #software, the number of #packages available on the server along with the method to copy them and use them when we reinstall our operating system(#OS).
Yum automatically refreshes the list of packages, whilst with apt-get you must execute a command 'apt-get update' to get the fresh packages.
To list of installed programs in #Linux:
1. Aptitude-based distributions (#Ubuntu, #Debian, etc): dpkg -l.
2. RPM-based distributions (#Fedora, #RHEL, etc): rpm -qa.
3. pkg*-based distributions (#OpenBSD, #FreeBSD, etc): pkg_info.
4. Portage-based distributions (#Gentoo, etc): equery list or eix -I.
5. pacman-based distributions (Arch Linux, etc): pacman -Q.

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How To Install MariaDB on Ubuntu Focal Fossa


This article will guide you on steps to install #MariaDB from the #Ubuntu #repositories and from the official MariaDB repositories. You can install MariaDB in two different ways.

To install MariaDB on Ubuntu, follow these steps:

1. Update #packages index. sudo apt update.

2. Once the packages list is updated, install MariaDB by issuing the following command: sudo apt install mariadb-server.

3. The MariaDB service will start automatically.

The default data directory for the MariaDB database server is /var/lib/mysql. The configuration file of MariaDB database server is /etc/mysql/mariadb. conf. d/50-server.

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Update Ubuntu from 16 04 to 18 04 via command line


This article will guide you on steps to #upgrade #Ubuntu #version.

To update Ubuntu using #terminal:

1. Open the terminal application.

2. For remote server use the ssh command to login (e.g. ssh user@server-name )

3. Fetch update software list by running #sudo apt-get update command.

4. Update Ubuntu #software by running sudo apt-get upgrade command.

5. Reboot the Ubuntu box if required by running sudo reboot.

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SQL Server and create a database on Ubuntu How to install


This article will guide you on how to #install MS SQL on #Ubuntu Server 18.04. 

To Install #Microsoft SQL Server 2017:

1. Visit Microsoft's official SQL Server 2017 download page.

2. Select the edition you want to #download. 

3. Click Download now below your selected edition. 

4. The wizard will prompt you to select an installation type. 

5. On the next page, select a directory for the installation folder.

To connect to the SQL Server using #SSMS:

i. From the Connect menu under the Object Explorer, choose the #Database Engine.

ii. Then, enter the information for the Server name (localhost), Authentication (SQL Server Authentication), and password for the sa user.

iii. Click the Connect button to connect to the SQL Server.

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Rewrite URLs with mod_rewrite for Apache on Ubuntu 16 04


This article will guide you on how to rewrite URLs with mod_rewrite in #Apache. Basically, mod_rewrite helps in creating human-readable URLs.

The URL #Rewrite #Module is an extension software for #IIS (Internet Information Services). URLs should be created so that they are easy to remember for the users and easy to find for the search engines. The URL Rewrite Module enables web administrators to develop and implement rules that assist them in this task.

htaccess rewrite rule includes setting a combination of rewrite condition ( #RewriteCond ) tests along with a corresponding rule ( #RewriteRule ) if the prior conditions pass. In most cases, these rules should be placed at any point after the RewriteEngine line.

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Deploy Laravel using Nginx on Ubuntu


This guide will help to set up Laravel with #Nginx on #Ubuntu 16.04. Laravel is the most popular, free, and open-source #PHP #framework in the world, known for its expressive and elegant syntax.
To move laravel project from localhost to production server, do:
1. Zip your #laravel app files.
2. Export your app's #database then set it up on your server.
3. After you have uploaded your laravel app files, open the . env file found on the root.
4. That's it!, now check your live #site.

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Steps To Harden OpenSSH Client on Ubuntu 18 04


This article will guide you on how to harden #OpenSSH Client by following some quick and easy steps.
#Hardening of the #OS is the act of configuring an OS securely, updating it, creating #rules and #policies to help govern the system in a secure manner, and removing unnecessary applications and services. This is done to minimize a computer OS's exposure to threats and to mitigate possible #risk.

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JupyterLab Environment on Ubuntu 18 04


This article will guide you on the process to set up a JupyterLab Environment on Ubuntu and made it accessible remotely. 

The JupyterLab Credential Store uses a password that you set upon first use. Each credential is encrypted with a hash of your password. The encrypted credentials are stored in the credentialstore file in the #directory you start #JupyterLab from.

You can also create new #environments from within Jupyter Notebook (home screen, Conda tab, and then click the plus sign). And you can create a notebook in any environment you want. Select the "Files" tab on the home screen and click the "New" dropdown menu, and in that menu select a Python environment from the list.

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Method to Install Software From Source on Ubuntu


This article will guide you on steps to #install #software from #source on #Ubuntu. The Complete #command is apt-get which is the easiest way to install files/Softwares #packages.

Once installed, on the command line, you can use dpkg --listfiles packagename . For instance, dpkg --listfiles firefox . 

If you want to see what files a package contains without installing it, then you can install apt-file and use that.

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SQL server error 17 Steps to fix it


This article will guide you on the steps to fix 'SQL Server does not exist or access denied' error which occurs when the computer running #Microsoft #SQL Server is not reachable.

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cURL 18 transfer closed with outstanding read data remaining


This article will guide you on the steps to fix cURL error 'cURL 18 transfer closed with outstanding read data remaining' which occurs while retrieving data from a #URL using a #cURL.

This #error can be fixed by correcting the permission of #directory '/var/cache/nginx'

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SQL error 15123


This article will guide you on the steps to troubleshoot and fix #SQL server #error #15123 which occurs in the process of changing or viewing the values of any advanced server configuration option.

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Fix SQL server error 18


When there is an issue with TLS version or encryption of an SQL server, an SQL server error 18 occurs.

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Method to fix Cloudflare error 527


When a #connection is interrupted between Cloudflare data center and an origin #Railgun server(rg-listener), thus a #Cloudflare error 527 will occur. This is influenced by loss of #packet data or a #firewall restriction in this situation.

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Fix Cloudflare error 1018


Cloudflare error 1018 is a common Cloudflare error which affects a domain whose DNS is hosted on the Cloudflare network in the case when cloudflare cannot resolve to the domain when trying to access it on a browser.


To resolve Cloudflare error 1016:

1. Verify your Cloudflare DNS settings include an A record that points to a valid IP address that resolves via a DNS lookup tool.

2. For a CNAME record pointing to a different domain, ensure that the target domain resolves via a DNS lookup tool.


Generally, to fix Cloudflare errors:

1. Contact your site administrator or hosting provider to eliminate these common causes.

2. Ensure your origin web server is responsive.

3. Review origin web server error logs to identify web server application crashes or outages.

4. Confirm Cloudflare IP addresses are not blocked or rate limited.

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How to securely back up your Linux Ubuntu Centos and Debian Server


#Backup and #restore refers to technologies and practices for making periodic copies of data and applications to a separate, secondary device and then using those copies to recover the data and applications—and the business operations on which they depend in the event that the original data and applications are lost.

#rsync uses what is called a delta-transfer algorithm which compares files from source and destination and sends only the differences between them.


To automatically backup #files and directories in Linux:

1. archive the content. Backing up your files using tar is very simple using the following command: # tar -cvpzf /backup/backupfilename.tar.gz /data/directory.

2. create backup script. Now let's add tar command in a bash script to make this backup process automatic.


#Rsync, or Remote Sync, is a free command-line tool that lets you transfer files and directories to local and remote destinations. 

Rsync is used for mirroring, performing backups, or migrating data to other servers.

Backing up file systems means copying file systems to removable media (such as tape) to safeguard against loss, damage, or corruption. 

Restoring file systems means copying reasonably current backup files from removable media to a working directory.

Data losses can be a very frustration encounter for a server owner. To avoid such catastrophic situations in losing your website data, it is very important to do a regular backup for your server and website.

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For Linux Tutorials

We create Linux HowTos and Tutorials for Sys Admins. Visit us on LinuxAPT.com

Also for Tech related tips, Visit forum.outsourcepath.com or General Technical tips on www.outsourcepath.com






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