How to Make DNF and YUM Save Downloaded RPM Packages

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DNF/YUM can automatically download the RPM packages and install them. Under some situations, we may prefer to make a copy of the RPM files for offline usage so that no need to have network connections to install the software packages. For such purposes, we need to make a copy of the RPM packages. It is
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Compress PNG Images on Linux

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PNG images already use DEFLATE data compression algorithm involving a combination of LZ77 and Huffman coding. But the PNG images can be further compressed by removing non-important metadata or using lossy compression to save storage space and/or data transfer bandwidth. In this post, we introduce 2 compression ways with tools available on Linux. Lossless compression
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Change Another Process’ Environment Variables in Linux

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Each process has its environment variables in Linux. But is it possible to change another process’ environment variable from another process in Linux? If it is possible to do so, how to do it? There is a trick which can work for some scenarios. First, find out the process ID, then start gdb and attach
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Redirect Feed Links to follow.it using .htaccess

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Feedburner used to a powerful tool for RSS feeds publishing and subscriber management. However, feedburner will unlikely leave its maintenance mode because there has been no new features yet less features for quite some years. But RSS feed is still an important part of the Web supported by many software such as WordPress. follow.it is
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Make Grub2 Boot Older Kernel Version in Ubuntu 20.04

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In a Linux system, we may have multiple kernels installed. Usually, it is the latest kernel configured to be the default one the system boot loader will use during automatic boot if there is no manual kernel choosing. In many cases, such as there is no driver ready yet for some devices in newer kernels,
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Add Inline Comments for Multi-line Command in Bash Script

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In Bash script, it is common that multiple small commands run together connected by pipes (|) and the whole command is quite long. For clarity, we may write the command in multiple lines. How to add comments for these long multi-line commands? In Bash, the content after # in a line is the comment. Using
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How to Match Multiple Lines using Regex in Perl One-liners

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Perl one-liners with perl’s regular expression statement can be a very powerful text processing tools used as commands in a terminal or a script. By default, the input to the perl one-liner with -p or -n options is passed line by line. However, when we want to match multiple lines, it gets us some trouble.
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How to Install Hyperledger Fabric 2.0 in Ubuntu 18.04

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Hyperledger Fabric is a consortium blockchain system. It’s performance is relatively good and its modular architecture enables it to be usable in many scenarios. Hyperledger Fabric itself has rich documents and samples of test networks. For beginners, deploying a new network for trying and testing still consumes quite some time. In this post, we will
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Grep 2 Lines using `grep` Command in Linux

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grep is excellent to match patterns from STDOUT/text files in command line or scripts. It’s handy. Sometimes, our problem is more complex than finding a keyword from a file. On a first thought, it may sound impossible using grep for such complex problems. But grep can be quite powerful than we thought. Today, let’s check
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How to Install Go 1.13.x on Ubuntu 18.04

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In Ubuntu 18.04 LTS, the default Go lang version is 1.10. For compatibility reason, the Ubuntu LTS will usually keep the major release version numbers for packages. However, many applications, such as Hyperledger Fabric 2.0, require a newer version of Go. In this post, let’s take a look at how to install a system level
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Dynamics 365 Developer Extension is Now Working in Visual Studio 2017

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I don’t know why Jason Lattimer’s D365DeveloperExensions no more working after VS 2017 release? It seems D365DeveloperExtensions anymore supported for newer Visual Studio version. I am pretty much sure, some of you may be still struggling with installing Dynamics 355 Developer extension for your Visual Studio 2017 community or professional edition. Not sure why this tool has been
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Bash Learning Materials

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Bash (GNU Bourne-Again SHell) the default shell for many Linux distributions. It is very common for scripting languages in Linux. Bash is easy and straightforward for writing small tools. However, as most tools, it has its grammars that could easily cause bugs if they are not used correctly. Here I summarize a list of good
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How to Install Wine 32-bit on CentOS 8

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Since version 7, RHEL and CentOS only have 64 bit versions. For some reasons, it’s better to run many Windows applications under 32 bit wine. Like How to Install Wine 32-bit on CentOS 7, this post introduce how to install 32-bit Wine on CentOS 8. Most of the mechanisms are similar yet there are differences.
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How to Convert Integers to Strings and Strings to Integers in PHP

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Conversion from integer to string and from string to integer are common operations in most applications such as C++. PHP has its uniqueness in language and standard library design. In this post, we will check methods to convert integers to strings and vice versa. Convert string to int in PHP You can cast a string
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How to list and start VirtualBox VMs in command line in Linux?

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VirtualBox is a nice open source virtual machine software. It works nicely on Linux and is supported by many Linux distros like Ubuntu in their official package repositories, so it is quite easy to set it up on Linux. The VMs can also be managed in command line using the vboxmanage command line tool provided
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Adding Gmail SMTP in Thunderbird

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Gmail’s authentication is secured by rejecting access from less secure apps. By default, adding Gmail SMTP in Thunderbird with your Google account password as SMTP authentication password will not work. And Google is beginning to shut off Google Account access to less secure apps. To solve this, the method is to use OAuth2 authentication instead
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How to synchronize OneDrive and OneDrive for Business files in Linux using Insync

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OneDrive is one of the good cloud storage services available and there is a business version called OneDrive for Business. Microsoft’s Office 365 plan is widely used including Exchange Email service and OneDrive for Business. However, there is no official client released yet for Linux users. Insync is a third party cloud storage syncing software
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