How to monitor OpenFlow messages with packet sniffer

As a key enabler for software-defined networking (SDN), OpenFlow was initially introduced in the academia as a way to enable innovation on production networks which had traditionally been built with closed and proprietary networking hardware. OpenFlow offloads the high-level routing/forwarding decisions (control plane) from networking devices such as switches, and moves the control plane on […]
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What are good web server benchmarking tools for Linux

As far as web server performance is concerned, there are many different factors at play, e.g., front-end application design, network latency/bandwidth, web server configuration, server-side in-memory cache, raw hardware capability, server load of shared hosting, etc. To compare and optimize web server performance under such a wide array of factors, we often perform load test […]
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How to disable Network Manager on Linux

Network Manager is a feature-rich network configuration service which is used by default in most Linux desktop environments nowadays. It provides automatic configuration of (wired/wireless) network interfaces, as well as VPN, mobile broadband and even Bluetooth connections. Network Manager is smart enough to automatically switch to the best (or the most recent) connection network, and […]
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How to block network traffic by country on Linux

As a system admin who maintains production Linux servers, there are circumstances where you need to selectively block or allow network traffic based on geographic locations. For example, you are experiencing denial-of-service attacks mostly originating from IP addresses registered with a particular country. In other cases, you want to block SSH logins from unknown foreign […]
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How to use Mutt email client with encrypted passwords

Mutt is an open-source email client written for Linux/UNIX terminal environment. Together with Alpine, Mutt has the most devoted followers among Linux command-line enthusiasts, and for good reasons. Think of anything you expect from an email client, and Mutt has it: multi-protocol support (e.g., POP3, IMAP and SMTP), S/MIME and PGP/GPG integration, threaded conversation, color […]
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How to send email notifications using Gmail SMTP server on Linux

Suppose you want to configure a Linux app to send out email messages from your server or desktop. The email messages can be part of email newsletters, status updates (e.g., Cachet), monitoring alerts (e.g., Monit), disk events (e.g., RAID mdadm), and so on. While you can set up your own outgoing mail server to deliver […]
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How to switch from NetworkManager to systemd-networkd on Linux

In the world of Linux, adoption of systemd has been a subject of heated controversy, and the debate between its proponents and critics is still going on. As of today, most major Linux distributions have adopted systemd as a default init system. Billed as a “never finished, never complete, but tracking progress of technology” by […]
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How to configure virtual hosts in Apache HTTP server

Virtual hosting refers to the technique that allows a physical server to host more than one website domain (e.g., site1.com, site2.com). Virtual hosting is prevalent in shared web hosting environments, where typically hundreds or more of websites or blogs are packed on a single dedicated server to amortize server maintenance cost. You are not a […]
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How to combine two graphs on Cacti

Cacti is a fantastic open source network monitoring system that is widely used to graph network elements like bandwidth, storage, processor and memory utilization. Using its web based interface, you can create and organize graphs easily. However, some advanced features like merging graphs, creating aggregate graphs using multiple sources, migration of Cacti to another server […]
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How to access a Linux server behind NAT via reverse SSH tunnel

You are running a Linux server at home, which is behind a NAT router or restrictive firewall. Now you want to SSH to the home server while you are away from home. How would you set that up? SSH port forwarding will certainly be an option. However, port forwarding can become tricky if you are […]
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