How to use on-screen virtual keyboard on Linux

On-screen virtual keyboard is an alternative input method that can replace a real hardware keyboard. Virtual keyboard may be a necessity in various cases. For example, your hardware keyboard is just broken; you do not have enough keyboards for extra machines; your hardware does not have an available port left to connect a keyboard; you […]
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How to sniff HTTP traffic from the command line on Linux

Suppose you want to sniff live HTTP web traffic (i.e., HTTP requests and responses) on the wire for some reason. For example, you may be testing experimental features of a web server. Or you may be debugging a web application or a RESTful service. Or you may be trying to troubleshoot PAC (proxy auto config) […]
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How to access Linux command cheat sheets from the command line

The power of Linux command line is its flexibility and versatility. Each Linux command comes with its share of command line options and parameters. Mix and match them, and even chain different commands with pipes and redirects. You get yourself literally hundreds of use cases even with a few basic commands, and it’s hard even […]
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How to manage DigitalOcean VPS droplets from the command line on Linux

DigitalOcean is one of the hottest new kids in the block in the cloud VPS hosting market. While not offering as comprehensive service portfolio as Amazon Web Services and the likes, DigitalOcean is already a strong contender for the best Linux-based cloud VPS service targeted at small businesses and developers, thanks to their competitive pricing […]
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How to check RPM package dependencies on Fedora, CentOS or RHEL

A typical RPM package on Red Hat-based systems requires all its dependent packages be installed to function properly. For end users, the complexity of such RPM dependency is hidden by package managers (e.g., yum or DNF) during package install/upgrade/removal process. However, if you are a sysadmin or a RPM maintainer, you need to be well-versed […]
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How to set up two-factor authentication for SSH login on Linux

With many high-profile password leaks nowadays, there is a lot of buzz in the industry on “multi-factor” authentication. In a multi-factor authentication system, users are required to go through two distinct authentication procedures: providing something they know (e.g., username/password), and leveraging something they have “physical” access to (e.g., one-time passcode generated by their mobile phone). […]
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How to repair a crashed WordPress database table

A WordPress database may experience failure and corruption under various circumstances. One of common problems with it is “crashed database.” When that happens, you will find the following error in WordPress error log: WordPress database error Table ‘./my_home/wp_posts’ is marked as crashed and last (automatic?) repair failed for query SELECT post_date_gmt FROM wp_posts WHERE post_status […]
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