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Using the SCP Command to Securely Copy Files [Examples]

Using the SCP Command

SCP or Secure Copy securely transfers files between two hosts over the network using the SSH protocol. This tutorial explains how to use this popular command with numerous examples. SCP is pre-installed with most Linux distributions and is often used for deploying software to servers and backing up – frequently automated using Bash Scripts. SCP Command Syntax scp OPTIONS SOURCE … TARGET SCP has a lot of options that are outlined on the commands manual, available by running: man scp Here’s a summary of the most commonly used options from the … Read more

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What Is a 500 Internal Server Error and How to Fix It?

500 Internal Server Error

This guide explores the 500 internal server error code, an HTTP error, and how to fix it. HTTP Errors and Error Codes Whenever a web page is loaded, a request is made to an HTTP server (Most web servers run Linux, by the way), and part of the response is a numeric status code that tells your web browser what kind of response it is. This allows the browser to handle the contents of the response correctly. Some example responses are: Status Code Meaning 200 … Read more

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How to Use the Dig Command [With Examples]

How to Use the Dig Command

dig is the Linux command-line tool used to look up the DNS records for a host. This tutorial explains how to use this command and includes handy examples. DNS records provide information to your computer about a host’s IP address on a network, email configuration, or other text data that can be associated with the host. DNS records provide the street directory for the internet. When you access a website, your computer looks up the DNS record associated with the website’s domain to get the IP … Read more

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Track Cisco BGP peers using Nagios

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Few will deny that monitoring of Cisco devices is essential part of sysadmin’s job. I personally use Nagios to track states of BGP neighbors on Cisco routers so if one of peers goes down I’ll receive a phone call from Nagios. You may have redundant network topology but it still makes sense to know when peer goes offline, how often it happens and how fast failover router (if any) pick-ups the traffic from failed peer. There are a few plugins for Nagios to monitoring BGP … Read more

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Nfsen: Traffic Classification

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Nfsen is open source sensor: it accepts netflow data from multiple netflow probes (servers, routers, vpn concentrators etc) and then visualizes it into human readable form. So using Nfsen you can see traffic statistics of every network device in your network in one place (actually Nfsen provides much more features).

By default Nfsen makes it possible to see only inbound and outbound traffic statistics but no protocol breakdown or any traffic classification. In the meantime it’s always useful to know what network applications are eating the bandwidth to understand if that fits baseline or not and take necessary actions. For example, if you’re monitoring Linux server which primary task is to host some website but in Nfsen you see that it generates 90% of SSH traffic and only 10% of web traffic then it would be reasonable idea to check if somebody is trying to brute force SSH password and stop that activity. In other words it’s better to have traffic statistics classified. In this article I’ll tell you how to enable traffic classification in Nfsen.


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Install nfdump and nfsen netflow tools in Linux

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Using nfsen it is possible to view IP traffic statistics on Linux interfaces including the graphs showing data sent and received (see the screenshot to the right) as well as historical information about all data transfers. So after you’ve configured nfsen and nfdump to monitor traffic on certain Linux server or router you’ll be able to answer the following example questions: What IP was downloading data through 48161 last Wednesday? or How many bytes were sent to IP via 53 port from Linux server? … Read more

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How to monitor traffic at Cisco router using Linux (Netflow)

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By default Cisco IOS doesn’t provide any traffic monitoring tools like iftop or iptraff available in Linux. While there are lots of proprietary solutions for this purpose including Cisco Netflow Collection, you are free to choose nfdump and nfsen open source software to monitor traffic of one or many Cisco routers and get detailed monitoring data through your Linux command line or as graphs at absolutely no cost. Below is beginner’s guide that helps to quickly deploy netflow collector and visualizer under Linux and impress … Read more