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Category: Howto

Building and running Google Chromium OS on Raspberry Pi 3

Foreword

I’ve been working on porting Google Chromium OS to various platforms in the last few months. One of the platforms is the very popular single board computer Raspberry Pi 3. Our team managed to successfuly build and run Chromium OS on it, and we have open sourced our work on Github.

This blog post is a re-post of the README.md document in our Github repository, which is also written by me. You are welcome to leave feedback on my blog or on Github.

Hapy hacking!

Table of contents

Introduction

This document describes how to build and run Google Chromium OS on Raspberry Pi, from its source code and the board overlay hosted in this repository.

This overlay can be used to build a Chromium OS image with Xorg/X11 as the graphics stack. As Google moved off from X since Chrome OS release 57, this overlay targets and was tested against the release 56 of Chromium OS.

This overlay and the document has been tested against Raspberry Pi 3 by the Flint team. It may also work on Pi 2 but is not tested, you are welcome to test it and send feedback.

About this repository

The code and document in this repository is the result of works by the people of the Flint team. We previously worked on this overlay internally and released a few disk images for Raspberry Pi to the public. Now we open this to the public.

Goal of this repository

  • To provide a open source code base that everybody can use to build and improve Chromium OS for Raspberry Pi.
  • To make as less change to the original Chromium OS code and process as possible, so that people can study and get used to the Chromium OS development process. We may provide scripts later to ease the process.

Typography Conventions

Shell commands running in the host OS are prefixed with the $ sign, like below.

$ cd /mydir

Shell commands running in the Chromium OS chroot environment are prefixed with (cr) $, like below.

(cr) $ cd /mydir         # This is a comment for the command. It should not be included in your command.

System requirement

  • A x86_64 system to perform the build. 64-bit hardware and OS are must. The Chromium OS is a very large project, building from the source form scratch usually takes hours to over 10 or even 20 hours, depends on the system configuration.
    • CPU: we recommend using a 4-core or higher processor. The Chromium OS build process runs in parallel so more cores can help shorten build time dramatically.

    • Memory: we recommend at least 8GB, plus enough swap space. Linking Chrome(the browser) could require more than 8GB of memory, so you will run into massive swapping or OOM if you have less memory.

    • Disk: at least 100GB of free space, 200GB or more is recommended. SSD could noticeably shorten the build time as there are many gigabytes of files need to be written to and read from the disk.

    • Network: total source code downloading will be over 10GB. A fast and stable Internet access is going to be very helpful.

  • A x86_64 Linux OS, it is called as the host OS later in this doc. The Chromium OS build process utilizes chroot to isolate the build environment from the host OS. So theoretically any modern Linux system should work. However, only limited Linux distros are tested by the Chromium OS team and the Flint team. Linux versions that are known to work:

    • Ubuntu Linux 14.04 & 16.04
    • Gentoo Linux
  • A non-root user account with sudo access. The build process should be run by this user, not the root user. The user need to have sudo access. For simplicity and convenience password-less sudo could be set for this user.

Prepare the system

Install necessary tools

Git and curl as the essential tools need to installed in the host OS. Python 2.7 is required to run scripts from Google depot_tools package. Python 3 support is marked as experimental by these scripts, so use it at your own risk, feedback are welcome.

Follow the usual way to install them on your host OS.

Install Google depot_tools

The depot_tools is a software package of scripts, provided by Google, to manage source code checkouts and code reviews. We need it to fetch the Chromium OS source code.

$ sudo mkdir -p /usr/local/repo
$ sudo chmod 777 /usr/local/repo
$ cd /usr/local/repo
$ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git

Then add depot_tools directory to PATH and setup proper umask for the user who is going to perform the build. Add below lines to the file ~/.bash_profile of that user. Or if you are using a different shell, handle that accordingly.

export PATH=/usr/local/repo/depot_tools:$PATH
umask 022

Then re-login to make above changes take effective.

Configure git

Better configure git now or it may complain in some operations later.

$ git config --global user.email "[email protected]"
$ git config --global user.name "Your Name"

Get Chromium OS source code

Create directory structure

The directory structure described here is a recommendation based on the best practice in the Flint team. You may host the files in a different way as you wish.

$ mkdir -p /project/chromiumos-R56      # This is the directory to hold Chromium OS source code.
$ mkdir -p /project/overlays            # This is the directory to hold this repository.

Fetch Chromium OS source code

Fetching of Chromium OS source code may take 10 to more than 30 minutes depends on your connection speed.

$ cd /project/chromiumos-R56
$ repo init -u https://chromium.googlesource.com/chromiumos/manifest.git --repo-url https://chromium.googlesource.com/external/repo.git -b release-R56-9000.B
$ repo sync -j8         # Raise this number if you have a fast Internet connection

Request for Google API key

If you would like to login into the Chromium OS GUI by using your Google ID, you will need to request for Google API key and include them in the disk image you build. Since the only authentication mechanism included in Chromium OS is Google ID, you probably will need this or you will only be able to login as guest user.

Apply for Google API on Google website per this document. After acquired the client ID, client secret and API key, put then in ~/.googleapikeys file as in below format.

'google_api_key': 'your api key',
'google_default_client_id': 'your client id',
'google_default_client_secret': 'your client secret',

Then the Chromium OS build script will read necessary information from this file automatically, and the image you build will allow Google ID login.

Setup Raspberry Pi overlay

Now fetch this overlay and put it in the right place.

$ cd /project/overlays
$ git clone https://github.com/flintinnovations/overlay-rpi.git

$ cd /project/chromiumos-R56/src/overlays
$ ln -s /project/overlays/overlay-rpi .

Then edit file /project/chromiumos-R56/src/third_party/chromiumos-overlay/eclass/cros-board.eclass, and put a line rpi in the ALL_BOARDS array, around line 29. It looks like this when done.

ALL_BOARDS=(
     rpi
     acorn
     amd64-corei7
     ....
)

Build Chromium OS for Raspberry Pi

Create the chroot

As mentioned above, a chroot environment will be used to run the actual build process and some other related tasks. To create the chroot environment, run below commands.

$ cd /project/chromiumos-R56
$ cros_sdk

It make take 10 to over 30 minutes depends on your Internet connection speed and disk speed. Once finished, it will enter into the chroot. The shell prompt string looks like below so it is very easy to tell whether you are currently in the chroot or not.

(cr) (release-R56-9000.B/(aaab1a3...)) <user>@<host> ~/trunk/src/scripts $

The chroot environment is located under the /project/chromiumos-R56/chroot directory.

Let’s exit from the chroot first as we need to do some customization before move on. Type exit or Ctrl + D to exit from the chroot shell.

Usually the chroot only needs to be created once and can be used to build a board many times or build different boards. It very rarely need to be removed/re-created.

Delete the chroot

If you would like to remove the chroot and re-create it from scratch, don’t delete the chroot directory directly. As there could be directories from the host OS bind mounted in the chroot, a rm chroot command could actually remove files from your host OS undesirably.

The correct way to remove the chroot is by using below commands.

$ cd /project/chromiumos-R56
$ cros_sdk --delete

Setup bind mount directories for chroot

Programs running inside the chroot will not be able to access files outside of the chroot. One way to circumvent this is to bind mount those files into a directory inside the chroot.

When entering the Chromium OS chroot environment, a file named .local_mounts will be checked and directories listed in it will be bind mounted inside the chroot. All we need to do is to create this file in the right place and put necessary contents in, by using below command.

$ echo "/project" > /project/chromiumos-R56/src/scripts/.local_mounts

Now, after entered the chroot, a /project directory will exist in the chroot and its content is the same as the /project directory in the host OS, as it actually is bind mounted from the host OS.

If we don’t do this, the /project/chromiumos-R56/src/overlays/overlay-rpi symbolic link will not be accessible, as the top directory (/project) it points to doesn’t exist in the chroot.

Enter the chroot

Now we can enter the chroot.

$ cd /project/chromiumos-R56
$ cros_sdk

It is the same command used to create the chroot. It creates the chroot if one does not exist, and enters the chroot if there is already one.

And we can check whether above .local_mounts setup was done correctly. Notice that the (cr) $ prefix denotes these commands should be run in the chroot.

(cr) $ ls /project                      # You should be able to see the same content as in host OS.
(cr) $ ls ../overlays/overlay-rpi/      # You should be able to see the content of this repo.

Move on if it works well. If not, check and make sure you set up .local_mounts correctly.

Set password for the chronos user

The chronos user is used to log into the command line interface of Chromium OS, via SSH, local console or the shell in crosh interface. It is recommended that a password is set for this user so you can login as this user and also can do sudo in the Chromium OS command line, for advanced tasks.

To set password for chronos user, run below command.

(cr) $ ./set_shared_user_password.sh

Type in a password when been prompted. If you would like to change the password, simply run the command again.

The password is encrypted and saved in the file /etc/shared_user_passwd.txt in the chroot. You only need to set it once and it will be used for all the images you build, unless you re-create the chroot.

Setup Raspberry Pi board

In the Chromium OS terminology, a board refers to a class of computer platform with distinct hardware configurations. The board will be used as a target in the process of building software packages and disk image for that specific computer platform.

There are many boards exist in the Chromium OS code base. They are either development platforms or real selling products running Chrome OS, such as Chromebooks you can buy from many vendors.

The Chromium OS project utilizes the Portage package management system from Gentoo Linux. Each board lives in its own “overlay”, which holds distinct build configuration, system configurations, collection of software packages, system services, disk image customization etc. for that board.

In our case here, we created a board named “rpi” and it refers to the Raspberry Pi computer. And we call the overlay “overlay-rpi” or “rpi”, all its files are hosted in this repository.

To build Chromium OS for a board, the first thing is to initialize the board from its overlay.

(cr) $ ./setup_board --board=rpi

Again, it may take 10 to over 30 minutes depends on the speed of your Internet connection and disk I/O.

After it’s done, a directory structure for the “rpi” board will be created under /build/rpi of the chroot.

Re-initialize the board

It is usually not necessary to re-initialize the board as what you have already built will be lost, and you will have to spend hours to rebuild all packages from scratch. But if you really need to do so, just re-run the same setup_board command with the ---force option.

(cr) $ ./setup_board --board=rpi --force

The --force option will remove the existing board directory /build/rpi and re-create it from scratch.

Build packages

Now it time to build all software packages for the rpi board.

(cr) $ ./build_packages --board=rpi

It may take hours depends on your processor power, your memory size, your disk speed and your Internet bandwidth. On a decent machine with 4 cores 8 threads, 16GB memory, files on regular HDD, and 100Mb broadband, it takes about 5 to 6 hours for the command to finish.

When interrupted

The build process is incremental. If it gets interrupted for any reason, you can always rerun the same build_packages command and it will resume the build instead of rebuild from scratch.

Read the output

The build_packages command throw out a lot of information on the console. Fortunately those information are very well organized.

  • Red text: these are error messages and very likely will cause the build process to break.
  • Green text: these are useful messages printed by the build script itself. They are useful when debugging problem.
  • White text: these are regular information that mostly are printed by the commands called in the build script. They provide more details about the build process thus are also useful for debugging.

Read the logs

Most time the build_packages command spends on is running the emerge commands, to build, install and pack those hundreds of software packages required by the overlay. The emerge command is from the portage system of Gentoo Linux.

The emerge command saves the output of its building, installation and packing process into log files. These files are extremely useful if there is failure when building some package. Those log files are located under the /build/rpi/tmp/portage/logs directory of the chroot. They are plain text files so can be viewed by tools like less, or more, or editors such as vim.

Build the disk image

After the build_packages command finished successfully, you can start building the disk image.

(cr) $ ./build_image --board=rpi --noenable_rootfs_verification

It may take 10 to 30 minutes, mainly depends on the speed of your disk. It is much faster on SSD than on HDD.

Find your image

After the command finished successfully, you will have disk images generated, saved under /mnt/host/source/src/build/images/rpi/ directory in the chroot, or /project/chromiumos-R56/src/build/images/rpi in the host OS. These two are the same directory, just bind mounted in the chroot.

Each invoke of the build_image command will create a directory named similar to R56-9000.104.<date time>-a1 under above directory. There is a symlink named latest under above directory, that always point to the image directory of the last successful build.

The disk image is usually named chromiumos_image.bin, under abovementioned directory. So full path to the latest image is

/mnt/host/source/src/build/images/rpi/latest/chromiumos_image.bin

in the chroot, and

/project/chromiumos-R56/src/build/images/rpi/latest/chromiumos_image.bin

in the host OS.

Boot Raspberry Pi from the image

The Raspberry Pi boots from the SD card so we need to write the previously generated disk image on to the SD card. A SD card of at least 8GB capacity is required.

Write the disk image to a SD card

There are two usual ways to write the Chromium OS disk image to a SD card. You can copy the image out to another Window/Mac/Linux system and write it using your favorite GUI/CLI application. It is the same as writing other Linux images for Raspberry Pi, so will not be explained here.

Another Chromium OS specific way is by using the cros command in the chroot.

Write the image by using the cros command

First plug the SD card into the box used to build the image and has the chroot. Then run below command.

(cr) $ cros flash usb:// rpi/latest

This asks to write the latest disk image to USB removable media. A list of USB removable media will be presented, with index number prefixed. You can select which USB drive to write to by type in the index number when prompted.

Boot from the SD card

After the disk image is successfully written to the SD card, plug it into the Raspberry Pi and boot it as usual. After a few seconds you will see a Chromium logo, later on it will boot into GUI mode and the first time setup screen will pop up for you to configure the system and login.

More information

Chromium OS Developer Guide. This is the official source of how to build Chromium OS

The Flint OS website, English site, our home 🙂

The Flint OS website, Chinese site, our home, in Chinese.

About us

We are a UK/China based technology start-up. We have offices in both London and Beijing at the moment and are looking to expand to the city of Shenzhen. The team of 3 founders have spent many years in technology, consulting and media industries and gained valuable experiences of how things work. We have also witnessed the trend of digital transformation and the disruption it has caused to businesses and individuals. Realizing there is the lack of simple, secure and reliable “IT-as-a-Service” offerings for businesses, schools and individuals, we decided to come together and founded Flint.

Flint began with a vision where all applications and services we use today will be living in the Cloud. With the ever advancing browser platform technology and web frontend performances, it’s not surprising that most things we do today with the internet can be done through a single browser window. We are stepping into an era where installable apps will soon become history.

Therefore, we built Flint OS – a simple, secure, fast and productive operating system. Based on the open-source Chromium Project that also powers the well-known Google Chromebooks. Flint OS inherits most of the benefits that Chromebooks have but also bundled with our enhancements and new features. We have turned Flint OS into a more open platform, users will no longer be forced to rely on Google services and have the freedom to choose whichever services they prefer. We have also made Flint OS run on a wider range of hardware platforms ranging from x86 PCs and ARM based single board computers, providing endless of possibilities and potentials of how Flint OS can be used and applied.

4 Comments

Get real time Telegram notification when SSH login on Linux

Traditionally, Linux system admins use commands such as last, lastlog or some log analysis service to monitor user logins and catch suspicious activities. This is a good security practice. However these methods have their drawbacks – as the usual approch is to do periodic scans there could be delay between a login event and the report of incident. The delay could be minutes to hours depends on how the system is configured.

In this post I’m going to introduce a way to get near real time notification when a user login event occurred. This method make use of the popular instant messaging cilent Telegram and its Bot API to send a notification on user login so the delay is usually within just a couple of seconds!

The basic idea

Telegram Bot is a special kind of account that operated by software instead of real human being. Telegram provides a HTTP API to control the bot, to do things like send a message, or receive a message and process it as command, etc. etc. I have made use of that feature to do following things:

  1. On user login, run a script.
  2. The script calls Telegram Bot API to send a message.
  3. The message is sent by Telegram server to my Telegram account.
  4. My Telegram client on phone and PC receive the message, I know a login event occured.

All this happends right after the user logs in. I usually got the notification from Telegram on PC within 2 secs. Keep reading to see how to set up this.

Setup a Telegram bot

First of all, you’ll need to have a Telegram account and create a Telegram bot. I won’t go into detail for this as it is easy and is already well documented on Telegram website. Check it out here.

Once the setup of bot is finished, a token will be allocated for the bot. Keep that token. It will be used by the script to control the bot via Telegram HTTP API.

Connect the bot with your Telegram account

For obvious reason regarding privacy, a Telegram bot cannot initiate a message to a Telegram user. If you need to received messsages from a bot, you need to first start a chat with it and send a hello message. This process is like talking to a readl human account, just talk to the bot and send any text is OK.

After you initiate the chat, the bot and you is now in a conversation which represents by an unique ID in Telegram API. We need to find out this conversation ID, as it will be the “destination” for our script to send notification message to.

Here is how to get that chat ID – first send a message to the bot, then access the Telegram API getUpdates.

The API URL is https://api.telegram.org/bot<your bot token>/getUpdates. HTTP method GET should be used to access it. <your bot token> is the token allocated to your bot, as mentioned above.

I use curl to do this.

$ curl "https://api.telegram.org/bot<bot token>/getUpdates"
{"ok":true,"result":[{"update_id":xxxxxxxxx,
"message":{"message_id":1954,"from":{"id":xxxxxxxxx,"first_name":"Your first name","last_name":"Your last name","username":"Your telegram user name"},"chat":{"id":xxxxxxxxx,"first_name":"Your first name","last_name":"Your last name","username":"username","type":"private"},"date":1494671101,"text":"test"}}]}

The return message is a JSON text. This is how it looks after beautification.

{
  "ok": true,
  "result": [{
    "update_id": xxxxxxxxx,
    "message": {
      "message_id": 1954,
      "from": {
        "id": xxxxxxxxx,
        "first_name": "Your first name",
        "last_name": "Your last name",
        "username": "username"
      },
      "chat": {
        "id": xxxxxxxxx,          <--- This is the chat ID you need.
        "first_name": "Your first name",
        "last_name": "Your last name",
        "username": "username",
        "type": "private"
      },
      "date": 1494671101,
      "text": "test"
    }
  }]
}

Note down the value of message.chat.id, we will need it in the script.

Create a script to send message via the bot

Now we need to create a script which sends a predefined message via Telelgram.

Create a executable script file named /usr/local/bin/tgbot.sh and put below content in.

#!/bin/bash

KEY="<your bot token>"

URL="https://api.telegram.org/bot$KEY/sendMessage"

TARGET="<your chat ID>" # Telegram ID of the conversation with the bot, get it from /getUpdates API

TEXT="User *$PAM_USER* logged in on *$HOSTNAME* at $(date '+%Y-%m-%d %H:%M:%S %Z')
Remote host: $PAM_RHOST
Remote user: $PAM_RUSER
Service: $PAM_SERVICE
TTY: $PAM_TTY"

PAYLOAD="chat_id=$TARGET&text=$TEXT&parse_mode=Markdown&disable_web_page_preview=true"

# Run in background so the script could return immediately without blocking PAM
curl -s --max-time 10 --retry 5 --retry-delay 2 --retry-max-time 10 -d "$PAYLOAD" $URL > /dev/null 2>&1 &

Remember to replace <your bot token> and <your chat ID> with the real data of your own.

Basically, this script use curl to access the Telegram HTTP API to send a text message to the designated user. Those $PAM_* variables are provided by PAM, they will be explained later.

You can now run this script to test. If everything goes right, your Telegram client will receieve a message like this:

User  logged in on myhost at 2017-05-13 18:45:20 CST
Remote host: 
Remote user: 
Service: 
TTY:

That means the script is working. The real useful information is still empty, they will be filled in when running by PAM.

Run the script when a user logs in on the server

Now the final part is to make the script running when a user logs in on the server.

There are some information available on the Internet regarding this topic, however most of them just put the command to run in the user’s shell init script, such as .bashrc, or /etc/profile or a script under /etc/profile.d/. This way works, but is not secure. Because a user have access to his own shell init scripts such as .bashrc or .zshrc, a hacker who steal the user’s identitiy and log in on the server can easily remove the command from the script or remove the script itself entirely. This makes it practically useless – the script will only be run just once and send out the notification once, then the hacker is able to mute it.

A better approach is to use the capability of PAM. I’ve introduced it in an earlier post, read it if you are not familiar with PAM yet.

Here we are going to use the pam_exec module to accomplish our goal. This module is part of the PAM and it can run a command specified by user. We can use it to run the Telegram message sending script on user login, then we will be able to accomplish our goal. Here is how.

Edit the file /etc/pam.d/system-auth, this is the PAM service that will be called by many system commands that tries to authenticate a user, SSH is one of them. Put below line at the last line.

session optional pam_exec.so type=open_session seteuid /usr/local/bin/tgbot.sh

This command tells PAM to run the script /usr/local/bin/tgbot.sh after a user successfully authenticated himself and logged into the system. The pam_exec module will export a few environment variables so the script could read them and send in the message. Below are the explaination of the variables.

PAM_USER: name of the user name who is logging in.
PAM_RHOST: the remote host that the user connects from.
PAM_RUSER: the user name on the remote host that the user connects from.
PAM_SERVICE: the PAM service, which in some way represents the system service that user trying to access.
PAM_TTY: if the user logs in locally, this will be the TTY name. For remote login via SSH, it will just be “ssh”.

These variables are send in the Telegram message, so we can now who from where on when has logged in on which server via which service, enough for us to know whether it normal or suspecious.

As this file is only writable by root, a non-root user could not bypass this step. This is much secure than the shell init script method. Of course, if the root user is hacked it still could be modified and the notification could be muted. Some further facility could be deployed to mitigate this problem, such as file integrity check, which is beyond the scope of this article.

Test it

Now login in to the server via SSH, and you will be able to recieve a message on Telegram from the bot, like in below screenshot. Congratulations!

More

In fact, this is just an demostration of the functionality of pam_exec and Telegram bot. You can actually do more. A few ideas is on my mind.

  • Trigger a system task such as mount a remote filesystem on user login via pam_exec.
  • Send a log to a remote server on user login via pam_exec.
  • Send notification via Telegram on failure of a critical system crontab.
  • Send notification via Telegram when system update is available.
  • And more….
7 Comments

Setup Free SSL with Let’s Encrypt and DNS validation

In this howto I’m going to talk about setup free SSL with Let’s Encrypt and DNS challenge validation on a Linux server, with auto-renew support. The free SSL certificates will work for both Nginx and Apache, the two most popular open source web servers.

Why use DNS challenge validation instead of web server validation

There are many articles on the Internet describing how to setup free SSL by using Let’s Encrypt. However most of them use web server challenge validation. This is great, though sometimes your web server setup don’t allow you to do that easily. There are several possible reasons to use DNS instead.

  • You have more than one web servers to serve your site, load balanced for example. You can’t tell in advance which server will respond to the challenges from Let’s Encrypt servers. There are solution for this situation but it is not trivial to setup.
  • Your web site runs in a intranet and no public access, thus unable to perform a web challenge validation.
  • You host quite a lot domains on your web server, you might want to avoid touching web server configurations to lower risks.
  • You have complex setup in your web server, such as all kinds of redirection between domains(non-www to www or vice versa, which is very common), mixed dynamic and static content, reverse caching proxies, firewalls etc., sometimes it might be hard to set it up quickly and correctly for web challenge validation.
  • You web server is managed by some other administrator and you don’t want to bother him.
  • You are building a new site and the web server is not up yet.
  • You want to keep another possible method on hand just in case.

Prerequisites

Your domain must be using one of the DNS providers that provide API access and is supported by the Lexicon DNS record manipulating tool. Check here for the full and up-to-date list of supported DNS service providers. Some commonly used DNS providers are in the list, such as AWS Route53, Cloudflare, Digital Ocean, EasyDNS, Namesilo, NS1, Rage4, Vultr.

If you are already using one of these providers to serve your domain, just move on. If you are not, I recommend you to try Cloudflare if possible. I’ll use Cloudflare as example in this howto.

Gather necessary information

First you need to log into your DNS providers’s website and get the required API access information. Take Cloudflare for example, after you logged in, click your email address at the top right corner of the page, then choose “My Settings” from the menu. This will open your account profile. Scroll down and you will see a section for API information, just like below.

Setup free SSL with Let's Encrypt and DNS validation

Click the “View API Key” button for Global API key, you will then see a popup text box with you key in it. We will need this key later. For different DNS providers, they may provide the API key in different but similar name, such as API token.

Install required software

This howto will use CentOS for example to demonstrate how to install necessary software packages. If you are using a different Linux distribution such as Ubuntu / Arch / Gentoo, the command line and package name might be a bit different. Leave a reply below if you don’t know how to find that out, I’m glad to help.

First install OpenSSL Git, Python, Pip.

yum install openssl git python python-pip

Then create a directory to hold the software we need to install from GitHub.

mkdir /usr/local/repo

Install Dehydrated, which is the tool to manage Let’s Encrypt SSL certificate. It can register, apply and renew certs for you.

git clone https://github.com/lukas2511/dehydrated.git /usr/local/repo/dehydrated

Then install Lexicon, a Python package that talks to DNS providers and manges DNS records. Dehydrated will use it to create DNS challenge validation record for Let’s Encryption.

pip install dns-lexicon
git clone https://github.com/AnalogJ/lexicon.git /usr/local/repo/lexicon

If you are using DNS provider other than Cloudflare demonstrated here, you may need to install extra dependencies for Lexicon, check for details here.

Configuration

Now you need to configure Dehydrated to tell it necessary information about the SSL certificate you would like to request. Create a new text file /etc/dehydrated/config and put below content in:

CHALLENGETYPE=dns-01
CONTACT_EMAIL=your_email_address
HOOK=/usr/local/repo/lexicon/examples/dehydrated.default.sh

Remember to put in your own email address for the second line. This configuration tells Dehydrated to use DNS challenge instead of the default web server challenge.

Then create file /etc/dehydrated/domains.txt to put in the domain name you would like to apply SSL certificate for. For example, if you have a domain example.com, and would like the certificate to work for hosts including www.example.com, forum.example.com, blog.example.com, then put a line as below in the file.

example.com www.example.com forum.example.com blog.example.com

Apply for Let’s Encrypt SSL certificate

Now you are ready to apply for the Let’s Encrypt SSL certificate for your domain. First is to register on Let’s Encrypt using the email address you provided earlier in the configuration.

/usr/local/repo/dehydrated/dehydrated --register --accept-terms

Then run below commands to apply for a new certificate

export LEXICON_CLOUDFLARE_USERNAME=your_cloudflare_account_email
export LEXICON_CLOUDFLARE_TOKEN=your_cloudflare_api_key
export PROVIDER=cloudflare
/usr/local/repo/dehydrated/dehydrated

This tells the dehydrated script to read the DNS configuration information from the environment variables. We do this just for quick setup. Later we will put them in a script for easier execution.

Once you started these commands, you will see output saying that Dehydrated is trying to request for certificate, setup DNS record etc. Once it’s finished, your certificate will be located under /etc/dehydrated/certs/ directory.

These commands are for Cloudflare. If you are using a different DNS provider, consult this link for corresponding parameters.

Setup web server

Now it’s time to tell your web server to use the certificates for your site. I’m using Nginx so below are the instruction for Nginx. If you need Apache information, please leave a message below and I’m glad to help.

Put below content in your Nginx configuration file. They can be in the http block if you only host example.com, or can be put in the server block for example.com if you host multiple different domains.

# Below 3 lines enhance SSL security
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers 'ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA';
ssl_prefer_server_ciphers on;
ssl_dhparam /etc/nginx/dhparam.pem;
# Change the file name in below two lines to your actual certificate names.
ssl_certificate /etc/dehydrated/certs/example.com/fullchain.pem;
ssl_certificate_key /etc/dehydrated/certs/example.com/privkey.pem;
ssl_session_cache shared:SSL:50m;
ssl_session_timeout 10m;

Make sure you change the two lines that refer to the certificate files to your actual file.

Then run below command to generate the dhparam file as referenced in above configuration. It may take a while depends on the hardware configuration of your server.

# openssl dhparam -out /etc/nginx/dhparam.pem 2048

After it is done, you can now run nginx -t to test your Nginx configuration. Make sure you see it says everything is OK before move on! A wrong configuration may take your site offline.

Now go to https://your.site.address, you will see your site loaded via HTTPS if you have done every step correctly.

Setup cron job for auto renewal

The Let’s Encrypt SSL certificate is free and easy to get, but it is only validate for 90 days. So you need to setup an scheduled job(called cron job on Linux) to check the remaining time of your certificates and renew it if necessary.

To do that, first create a script with below content, and save it as /usr/local/sbin/letsencrypt.sh

#!/bin/bash

export LEXICON_CLOUDFLARE_USERNAME=your_cloudflare_account_email
export LEXICON_CLOUDFLARE_TOKEN=your_cloudflare_api_key
export PROVIDER=cloudflare

/usr/local/repo/dehydrated/dehydrated --cron

nginx -s reload

Again, remember to put correct DNS parameters as your actual situation. And remind that the dehydrated command has a “–cron” option. This option takes care of necessary certificate expiration check and renew process. The last command reloads Nginx so if the cerificates are renewed nginx will pick them up.

Then make the script executable and scheduled to run every week.

chmod +x /usr/local/sbin/letsencrypt.sh
ln -s /usr/local/sbin/letsencrypt.sh /etc/cron.weekly/letsencrypt.sh

Congratulations!

Now you have finished setup of Let’s Encrypt free SSL certificate, you site now serves content via the much safer HTTPS protocol, and you have auto renew in place. Enjoy it.

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