All posts by Sumarsono

Linux

How To Set Up an OpenVPN Server on Ubuntu 14.04

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How To Set Up an OpenVPN Server on Ubuntu 14.04

Introduction

Want to access the Internet safely and securely from your smartphone or laptop when connected to an untrusted network such as the WiFi of a hotel or coffee shop? A Virtual Private Network (VPN) allows you to traverse untrusted networks privately and securely to your DigitalOcean Droplet as if you were on a secure and private network. The traffic emerges from the Droplet and continues its journey to the destination.

When combined with HTTPS connections, this setup allows you to secure your wireless logins and transactions. You can circumvent geographical restrictions and censorship, and shield your location and unencrypted HTTP traffic from the untrusted network.

OpenVPN is a full-featured open source Secure Socket Layer (SSL) VPN solution that accommodates a wide range of configurations. In this tutorial, we’ll set up an OpenVPN server on a Droplet and then configure access to it from Windows, OS X, iOS and Android. This tutorial will keep the installation and configuration steps as simple as possible for these setups.

Note: OpenVPN can be installed automatically on your Droplet by adding this script to its User Data when launching it. Check out this tutorial to learn more about Droplet User Data.

Continue reading How To Set Up an OpenVPN Server on Ubuntu 14.04 →

Linux

How To Set Up Apache Virtual Hosts on Ubuntu 14.04 LTS

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How To Set Up Apache Virtual Hosts on Ubuntu 14.04 LTS

Introduction

The Apache web server is the most popular way of serving web content on the internet. It accounts for more than half of all active websites on the internet and is extremely powerful and flexible.

Apache breaks its functionality and components into individual units that can be customized and configured independently. The basic unit that describes an individual site or domain is called a virtual host.

These designations allow the administrator to use one server to host multiple domains or sites off of a single interface or IP by using a matching mechanism. This is relevant to anyone looking to host more than one site off of a single VPS.

Each domain that is configured will direct the visitor to a specific directory holding that site’s information, never indicating that the same server is also responsible for other sites. This scheme is expandable without any software limit as long as your server can handle the load.

In this guide, we will walk you through how to set up Apache virtual hosts on an Ubuntu 14.04 VPS. During this process, you’ll learn how to serve different content to different visitors depending on which domains they are requesting. Continue reading How To Set Up Apache Virtual Hosts on Ubuntu 14.04 LTS →

Linux

How To Set Up SSH Keys

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How To Set Up SSH Keys

About SSH Keys

SSH keys provide a more secure way of logging into a virtual private server with SSH than using a password alone. While a password can eventually be cracked with a brute force attack, SSH keys are nearly impossible to decipher by brute force alone. Generating a key pair provides you with two long string of characters: a public and a private key. You can place the public key on any server, and then unlock it by connecting to it with a client that already has the private key. When the two match up, the system unlocks without the need for a password. You can increase security even more by protecting the private key with a passphrase.

Step One—Create the RSA Key Pair

The first step is to create the key pair on the client machine (there is a good chance that this will just be your computer): Continue reading How To Set Up SSH Keys →

Linux

Add Swap on Ubuntu 14.04

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How To Add Swap on Ubuntu 14.04

Introduction

One of the easiest way of increasing the responsiveness of your server and guarding against out of memory errors in your applications is to add some swap space. Swap is an area on a hard drive that has been designated as a place where the operating system can temporarily store data that it can no longer hold in RAM.

Basically, this gives you the ability to increase the amount of information that your server can keep in its working “memory”, with some caveats. The space on the hard drive will be used mainly when space in RAM is no longer sufficient for data.

The information written to disk will be slower than information kept in RAM, but the operating system will prefer to keep running application data in memory and use swap for the older data. Overall, having swap space as a fall back for when your system’s RAM is depleted is a good safety net.

In this guide, we’ll cover how to create and enable a swap file on an Ubuntu 14.04 server.

Check the System for Swap Information

Before we begin, we will take a look at our operating system to see if we already have some swap space available. We can have multiple swap files or swap partitions, but generally one should be enough.

We can see if the system has any configured swap by typing: Continue reading Add Swap on Ubuntu 14.04 →

Linux

Understanding the Nginx Configuration File Structure and Configuration Contexts

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Understanding the Nginx Configuration File Structure and Configuration Contexts

Introduction

Nginx is a high performance web server that is responsible for handling the load of some of the largest sites on the internet. It is especially good at handling many concurrent connections and excels at serving static content.

While many users are aware of Nginx’s capabilities, new users are often confused by some of the conventions they find in Nginx configuration files. In this guide, we will focus on discussing the basic structure of an Nginx configuration file along with some guidelines on how to design your files.

Understanding Nginx Configuration Contexts

This guide will cover the basic structure found in the main Nginx configuration file. The location of this file will vary depending on how you installed the software on your machine. For many distributions, the file will be located at /etc/nginx/nginx.conf. If it does not exist there, it may also be at /usr/local/nginx/conf/nginx.conf or /usr/local/etc/nginx/nginx.conf.

One of the first things that you should notice when looking at the main configuration file is that it appears to be organized in a tree-like structure, defined by sets of brackets (that look like { and }). In Nginx parlance, the areas that these brackets define are called “contexts” because they contain configuration details that are separated according to their area of concern. Basically, these divisions provide an organizational structure along with some conditional logic to decide whether to apply the configurations within.

Because contexts can be layered within one another, Nginx provides a level of directive inheritance. As a general rule, if a directive is valid in multiple nested scopes, a declaration in a broader context will be passed on to any child contexts as default values. The children contexts can override these values at will. It is worth noting that an override to any array-type directives will replace the previous value, not append to it.

Directives can only be used in the contexts that they were designed for. Nginx will error out on reading a configuration file with directives that are declared in the wrong context. The Nginx documentation contains information about which contexts each directive is valid in, so it is a great reference if you are unsure.

Below, we’ll discuss the most common contexts that you’re likely to come across when working with Nginx. Continue reading Understanding the Nginx Configuration File Structure and Configuration Contexts →

Linux

Set Up Nginx Server Blocks (Virtual Hosts) on Ubuntu 14.04 LTS

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Introduction

When using the Nginx web server, server blocks (similar to the virtual hosts in Apache) can be used to encapsulate configuration details and host more than one domain off of a single server.

In this guide, we’ll discuss how to configure server blocks in Nginx on an Ubuntu 14.04 server.

Prerequisites

We’re going to be using a non-root user with sudo privileges throughout this tutorial. If you do not have a user like this configured, you can make one by following steps 1-4 in our Ubuntu 14.04 initial server setup guide.

You will also need to have Nginx installed on your server. If you want an entire LEMP (Linux, Nginx, MySQL, and PHP) stack on your server, you can follow our guide on setting up a LEMP stack in Ubuntu 14.04. If you only need Nginx, you can install it by typing:

sudo apt-get update
sudo apt-get install nginx

When you have fulfilled these requirements, you can continue on with this guide.

For demonstration purposes, we’re going to set up two domains with our Nginx server. The domain names we’ll use in this guide are example.com and test.com.

You can find a guide on how to set up domain names with DigitalOcean here. If you do not have two spare domain names to play with, use dummy names for now and we’ll show you later how to configure your local computer to test your configuration.

Step One — Set Up New Document Root Directories

By default, Nginx on Ubuntu 14.04 has one server block enabled by default. It is configured to serve documents out of a directory at:

/usr/share/nginx/html

We won’t use the default since it is easier to work with things in the /var/www directory. Ubuntu’s Nginx package does not use /var/www as its document root by default due to a Debian policy about packages utilizing /var/www. Continue reading Set Up Nginx Server Blocks (Virtual Hosts) on Ubuntu 14.04 LTS →

Linux

Install Linux, nginx, MySQL, PHP (LEMP) stack on Ubuntu 14.04

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Introduction

The LEMP software stack is a group of software that can be used to serve dynamic web pages and web applications. This is an acronym that describes a Linux operating system, with an Nginx web server. The backend data is stored in MySQL and the dynamic processing is handled by PHP.

In this guide, we will demonstrate how to install a LEMP stack on an Ubuntu 14.04 server. The Ubuntu operating system takes care of the first requirement. We will describe how to get the rest of the components up and running.

Note: The LEMP Stack can be installed automatically on your Droplet by adding this script to its User Data when launching it. Check out this tutorial to learn more about Droplet User Data.

Prerequisites

Before you complete this tutorial, you should have a regular, non-root user account on your server with sudo privileges. You can learn how to set up this type of account by completing steps 1-4 in our Ubuntu 14.04 initial server setup.

Once you have your account available, sign into your server with that username. You are now ready to begin the steps outlined in this guide. Continue reading Install Linux, nginx, MySQL, PHP (LEMP) stack on Ubuntu 14.04 →

Linux

Initial Server Setup with Ubuntu 14.04

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Introduction

When you first create a new Ubuntu 14.04 server, there are a few configuration steps that you should take early on as part of the basic setup. This will increase the security and usability of your server and will give you a solid foundation for subsequent actions.

Step One — Root Login

To log into your server, you will need to know your server’s public IP address and the password for the “root” user’s account. If you have not already logged into your server, you may want to follow the first tutorial in this series, How to Connect to Your Droplet with SSH, which covers this process in detail.

If you are not already connected to your server, go ahead and log in as the root user using the following command (substitute the highlighted word with your server’s public IP address):

  • ssh root@SERVER_IP_ADDRESS

Complete the login process by accepting the warning about host authenticity, if it appears, then providing your root authentication (password or private key). If it is your first time logging into the server, with a password, you will also be prompted to change the root password.

About Root

The root user is the administrative user in a Linux environment that has very broad privileges. Because of the heightened privileges of the root account, you are actually discouraged from using it on a regular basis. This is because part of the power inherent with the root account is the ability to make very destructive changes, even by accident.

The next step is to set up an alternative user account with a reduced scope of influence for day-to-day work. We’ll teach you how to gain increased privileges during the times when you need them. Continue reading Initial Server Setup with Ubuntu 14.04 →

Linux

Install Graylog2 And Centralize Logs On Ubuntu 14.04

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Introduction

In this tutorial, we will cover the installation of Graylog2 (v0.20.2), and configure it to gather the syslogs of our systems in a centralized location. Graylog2 is a powerful log management and analysis tool that has many use cases, from monitoring SSH logins and unusual activity to debugging applications. It is based on Elasticsearch, Java, MongoDB, and Scala.

It is possible to use Graylog2 to gather and monitor a large variety of logs, but we will limit the scope of this tutorial to syslog gathering. Also, because we are demonstrating the basics of Graylog2, we will be installing all of the components on a single server.

About Graylog2 Components

Graylog2 has four main components:

  • Graylog2 Server nodes: Serves as a worker that receives and processes messages, and communicates with all other non-server components. Its performance is CPU dependent
  • Elasticsearch nodes: Stores all of the logs/messages. Its performance is RAM and disk I/O dependent
  • MongoDB: Stores metadata and does not experience much load
  • Web Interface: The user interface

Here is a diagram of the Graylog2 components (note that the messages are sent from your other servers):

Basic Graylog2 Setup

For a very basic setup, all of the components can be installed on the same server. For a larger, production setup, it would be wise to set up some high-availability features because if the server, Elasticsearch, or MongoDB components experiences an outage, Graylog2 will not gather the messages generated during the outage. Continue reading Install Graylog2 And Centralize Logs On Ubuntu 14.04 →

Linux

Troubleshoot Common HTTP Error Codes

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How To Troubleshoot Common HTTP Error Codes

Introduction

When accessing a web server or application, every HTTP request that is received by a server is responded to with an HTTP status code. HTTP status codes are three-digit codes, and are grouped into five different classes. The class of a status code can be quickly identified by its first digit:

  • 1xx: Informational
  • 2xx: Success
  • 3xx: Redirection
  • 4xx: Client Error
  • 5xx: Server Error

This guide focuses on identifying and troubleshooting the most commonly encountered HTTP error codes, i.e. 4xx and 5xx status codes, from a system administrator’s perspective. There are many situations that could cause a web server to respond to a request with a particular error code–we will cover common potential causes and solutions.

Client and Server Error Overview

Client errors, or HTTP status codes from 400 to 499, are the result of HTTP requests sent by a user client (i.e. a web browser or other HTTP client). Even though these types of errors are client-related, it is often useful to know which error code a user is encountering to determine if the potential issue can be fixed by server configuration.

Server errors, or HTTP status codes from 500 to 599, are returned by a web server when it is aware that an error has occurred or is otherwise not able to process the request.

General Troubleshooting Tips

  • When using a web browser to test a web server, refresh the browser after making server changes
  • Check server logs for more details about how the server is handling the requests. For example, web servers such as Apache or Nginx produce two files called access.log and error.log that can be scanned for relevant information
  • Keep in mind that HTTP status code definitions are part of a standard that is implemented by the application that is serving requests. This means that the actual status code that is returned depends on how the server software handles a particular error–this guide should generally point you in the right direction

Now that you have a high-level understanding of HTTP status codes, we will look at the commonly encountered errors. Continue reading Troubleshoot Common HTTP Error Codes →