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@ -1,5 +1,5 @@
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[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: translator: (qfzy1233)
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
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@ -1,144 +0,0 @@
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[#]: collector: (lujun9972)
|
||||
[#]: translator: (lxbwolf)
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (Drop PNG and JPG for your online images: Use WebP)
|
||||
[#]: via: (https://opensource.com/article/20/4/webp-image-compression)
|
||||
[#]: author: (Jeff Macharyas https://opensource.com/users/jeffmacharyas)
|
||||
|
||||
Drop PNG and JPG for your online images: Use WebP
|
||||
======
|
||||
Get started with this open source image editing tool to save time and
|
||||
space.
|
||||
![Painting art on a computer screen][1]
|
||||
|
||||
WebP is an image format developed by Google in 2010 that provides superior lossless and lossy compression for images on the web. Using WebP, web developers can create smaller, richer images that improve site speed. A faster loading website is critical to the user experience and for the website's marketing effectiveness.
|
||||
|
||||
For optimal loading across all devices and users, images on your site should not be larger than 500 KB in file size.
|
||||
|
||||
WebP lossless images are often at least 25% smaller in size compared to PNGs. WebP lossy images are often anywhere from 25-34% smaller than comparable JPEG images at equivalent SSIM (structural similarity) quality index.
|
||||
|
||||
Lossless WebP supports transparency, as well. For cases when lossy RGB compression is acceptable, lossy WebP also supports transparency, typically providing three times smaller file sizes compared to PNG.
|
||||
|
||||
Google reports a 64% reduction in file size for images converted from animated GIFs to lossy WebP, and a 19% reduction when converted to lossless WebP.
|
||||
|
||||
The WebP file format is based on the RIFF (resource interchange file format) document format. The file signature is **52 49 46 46** (RIFF), as you can see with [hexdump][2]:
|
||||
|
||||
|
||||
```
|
||||
$ hexdump --canonical pixel.webp
|
||||
00000000 52 49 46 46 26 00 00 00 [...] |RIFF&...WEBPVP8 |
|
||||
00000010 1a 00 00 00 30 01 00 9d [...] |....0....*......|
|
||||
00000020 0e 25 a4 00 03 70 00 fe [...] |.%...p...`....|
|
||||
0000002e
|
||||
```
|
||||
|
||||
The standalone libwebp library serves as a reference implementation for the WebP specification and is available from Google's [Git repository][3] or as a tarball.
|
||||
|
||||
The WebP format is compatible with 80% of the web browsers in use worldwide. At the time of this writing, it is not compatible with Apple's Safari browser. The workaround for this is to serve up a JPG/PNG alongside a WebP, and there are methods and Wordpress plugins to do that.
|
||||
|
||||
### Why does this matter?
|
||||
|
||||
Part of my job is to design and maintain our organization's website. Since the website is a marketing tool and site speed is a critical aspect of the user experience, I have been working to improve the speed, and reducing image sizes by converting them to WebP has been a good solution.
|
||||
|
||||
To test the speed of one of the pages, I turned to **web.dev**, which is powered by Lighthouse, released under the Apache 2.0 license, and can be found at <https://github.com/GoogleChrome/lighthouse>.
|
||||
|
||||
According to its official description, "Lighthouse is an open source, automated tool for improving the quality of web pages. You can run it against any web page—public or requiring authentication. It has audits for performance, accessibility, progressive web apps, SEO, and more. You can run Lighthouse in Chrome DevTools, from the command line, or as a Node module. You give Lighthouse a URL to audit, it runs a series of audits against the page, and then it generates a report on how well the page did. From there, use the failing audits as indicators on how to improve the page. Each audit has a reference doc explaining why the audit is important, as well as how to fix it."
|
||||
|
||||
### Creating a smaller WebP image
|
||||
|
||||
The page I tested returned three images. In the report it generates, it provides recommendations and targets. I chose the "app-graphic" image, which, it reported, is 650 KB. By converting it to WebP, I should save 589 KB, reducing the image to 61 KB. I converted the image in Photoshop and saved it with the default WebP settings, and it returned a file size of 44.9 KB. Better than expected! As the screenshot from Photoshop shows, the images look identical in visual quality.
|
||||
|
||||
![WebP vs JPG comparison][4]
|
||||
|
||||
On the left: 650 KB (actual size). On the right: 589 KB (target size after conversion).
|
||||
|
||||
Of course, the open source image editor [GIMP][5] also supports WebP as an export format. It offers several options for quality and compression profile:
|
||||
|
||||
![GIMP dialog for exporting webp, as a webp][6]
|
||||
|
||||
A zoomed-in look of another image:
|
||||
|
||||
![WebP vs PNG comparison][7]
|
||||
|
||||
PNG (left) and WebP (right), both converted from a JPG, shows the WebP, although smaller in size, is superior in visual quality.
|
||||
|
||||
### Convert to an image to WebP
|
||||
|
||||
To convert images on Linux from JPG/PNG to WebP, you can also use the command-line:
|
||||
|
||||
Use **cwebp** on the command line to convert PNG or JPG image files to WebP format. You can convert a PNG image file to a WebP image with a quality range of 80 with the command:
|
||||
|
||||
|
||||
```
|
||||
`cwebp -q 80 image.png -o image.webp`
|
||||
```
|
||||
|
||||
Alternatively, you can also use [Image Magick][8], which is probably available in your distribution's software repository. The subcommand for conversion is **convert**, and all that's needed is an input and output file:
|
||||
|
||||
|
||||
```
|
||||
`convert pixel.png pixel.webp`
|
||||
```
|
||||
|
||||
### Convert an image to WebP with an editor
|
||||
|
||||
To convert images to WebP with a photo editor, use [GIMP][9]. From version 2.10 on, it supports WebP natively.
|
||||
|
||||
If you're a Photoshop user, you need a plugin to convert the files, as Photoshop does not include it natively. WebPShop 0.2.1, released under the Apache License 2.0 license, is a Photoshop module for opening and saving WebP images, including animations, and can be found at: <https://github.com/webmproject/WebPShop>.
|
||||
|
||||
To use the plugin, put the file found in the **bin** folder inside your Photoshop plugin directory:
|
||||
|
||||
Windows x64—C:\Program Files\Adobe\Adobe Photoshop\Plug-ins\WebPShop.8bi
|
||||
|
||||
Mac—Applications/Adobe Photoshop/Plug-ins/WebPShop.plugin
|
||||
|
||||
### WebP on Wordpress
|
||||
|
||||
Many websites are built using Wordpress (that's what I use). So, how does Wordpress handle uploading WebP images? At the time of this writing, it doesn't. But, there are, of course, plugins to enable it so you can serve up both WebP alongside PNG/JPG images (for the Apple crowd).
|
||||
|
||||
Or there are these [instructions][10] from [Marius Hosting][11]:
|
||||
|
||||
"How about directly uploading WebP images to Wordpress? This is easy. Just add some text line on your theme functions.php file. Wordpress does not natively support viewing and uploading WebP files, but I will explain to you how you can make it work in a few simple steps. Log in to your Wordpress admin area and go to Appearance/Theme Editor and find functions.php. Copy and paste the code below at the end of the file and save it.
|
||||
|
||||
|
||||
```
|
||||
`//** *Enable upload for webp image files.*/ function webp_upload_mimes($existing_mimes) { $existing_mimes['webp'] = 'image/webp'; return $existing_mimes; } add_filter('mime_types', 'webp_upload_mimes');`
|
||||
```
|
||||
|
||||
If you want to see the thumbnail image preview when you go to Media/Library, you have to add the code below in the same functions.php file. To find the functions.php file, go to Appearance/Theme Editor and find functions.php, then copy and paste the code below at the end of the file and save it."
|
||||
|
||||
|
||||
```
|
||||
`//** * Enable preview / thumbnail for webp image files.*/ function webp_is_displayable($result, $path) { if ($result === false) { $displayable_image_types = array( IMAGETYPE_WEBP ); $info = @getimagesize( $path ); if (empty($info)) { $result = false; } elseif (!in_array($info[2], $displayable_image_types)) { $result = false; } else { $result = true; } } return $result; } add_filter('file_is_displayable_image', 'webp_is_displayable', 10, 2);`
|
||||
```
|
||||
|
||||
### WebP and the future
|
||||
|
||||
WebP is a robust and optimized format. It looks better, it has better compression ratio, and it has all the features of most other common image formats. There's no need to wait—start using it now.
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/20/4/webp-image-compression
|
||||
|
||||
作者：[Jeff Macharyas][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/jeffmacharyas
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/painting_computer_screen_art_design_creative.png?itok=LVAeQx3_ (Painting art on a computer screen)
|
||||
[2]: https://opensource.com/article/19/8/dig-binary-files-hexdump
|
||||
[3]: https://storage.googleapis.com/downloads.webmproject.org/releases/webp/index.html
|
||||
[4]: https://opensource.com/sites/default/files/uploads/webp-vs-jpg-app-graphic.png (WebP vs JPG comparison)
|
||||
[5]: http://gimp.org
|
||||
[6]: https://opensource.com/sites/default/files/webp-gimp.webp (GIMP dialog for exporting webp, as a webp)
|
||||
[7]: https://opensource.com/sites/default/files/uploads/xcompare-png-left-webp-right.png (WebP vs PNG comparison)
|
||||
[8]: https://imagemagick.org
|
||||
[9]: https://en.wikipedia.org/wiki/GIMP
|
||||
[10]: https://mariushosting.com/how-to-upload-webp-files-on-wordpress/
|
||||
[11]: https://mariushosting.com/
|
||||
@ -0,0 +1,108 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (4 cool new projects to try in COPR for May 2020)
|
||||
[#]: via: (https://fedoramagazine.org/4-cool-new-projects-to-try-in-copr-for-april-2020/)
|
||||
[#]: author: (Dominik Turecek https://fedoramagazine.org/author/dturecek/)
|
||||
|
||||
4 cool new projects to try in COPR for May 2020
|
||||
======
|
||||
|
||||
![][1]
|
||||
|
||||
COPR is a [collection][2] of personal repositories for software that isn’t carried in Fedora. Some software doesn’t conform to standards that allow easy packaging. Or it may not meet other Fedora standards, despite being free and open source. COPR can offer these projects outside the Fedora set of packages. Software in COPR isn’t supported by Fedora infrastructure or signed by the project. However, it can be a neat way to try new or experimental software.
|
||||
|
||||
This article presents a few new and interesting projects in COPR. If you’re new to using COPR, see the [COPR User Documentation][3] for how to get started.
|
||||
|
||||
### Ytop
|
||||
|
||||
[Ytop][4] is a command-line system monitor similar to _htop_. The main difference between them is that _ytop_, on top of showing processes and their CPU and memory usage, shows graphs of system CPU, memory, and network usage over time. Additionally, _ytop_ shows disk usage and temperatures of the machine. Finally, _ytop_ supports multiple color schemes as well as an option to create new ones.
|
||||
|
||||
![][5]
|
||||
|
||||
#### Installation instructions
|
||||
|
||||
The [repo][6] currently provides _ytop_ for Fedora 30, 31, 32, and Rawhide, as well as EPEL 7. To install _ytop_, use these commands [with _sudo_][7]:
|
||||
|
||||
```
|
||||
sudo dnf copr enable atim/ytop
|
||||
sudo dnf install ytop
|
||||
```
|
||||
|
||||
### Ctop
|
||||
|
||||
[Ctop][8] is yet another command-line system monitor. However, unlike _htop_ and _ytop_, _ctop_ focuses on showing resource usage of containers. _Ctop_ shows both an overview of CPU, memory, network and disk usage of all containers running on your machine, and more comprehensive information about a single container, including graphs of resource usage over time. Currently, _ctop_ has support for Docker and runc containers.
|
||||
|
||||
![][9]
|
||||
|
||||
#### Installation instructions
|
||||
|
||||
The [repo][10] currently provides _ctop_ for Fedora 31, 32 and Rawhide, EPEL 7, as well as for other distributions. To install _ctop_, use these commands:
|
||||
|
||||
```
|
||||
sudo dnf copr enable fuhrmann/ctop
|
||||
sudo dnf install ctop
|
||||
```
|
||||
|
||||
### Shortwave
|
||||
|
||||
[Shortwave][11] is a program for listening to radio stations. Shortwave uses a community database of radio stations [www.radio-browser.info][12]. In this database, you can discover or search for radio stations, add them to your library, and listen to them. Additionally, Shortwave provides information about currently playing song and can record the songs as well.
|
||||
|
||||
![][13]
|
||||
|
||||
#### Installation instructions
|
||||
|
||||
The [repo][14] currently provides Shortwave for Fedora 31, 32, and Rawhide. To install Shortwave, use these commands:
|
||||
|
||||
```
|
||||
sudo dnf copr enable atim/shortwave
|
||||
sudo dnf install shortwave
|
||||
```
|
||||
|
||||
### Setzer
|
||||
|
||||
[Setzer][15] is a LaTeX editor that can build pdf documents and view them as well. It provides templates for various types of documents, such as articles or presentation slides. Additionally, Setzer has buttons for a lot of special symbols, math symbols and greek letters.
|
||||
|
||||
![][16]
|
||||
|
||||
#### Installation instructions
|
||||
|
||||
The [repo][17] currently provides Setzer for Fedora 30, 31, 32, and Rawhide. To install Setzer, use these commands:
|
||||
|
||||
```
|
||||
sudo dnf copr enable lyessaadi/setzer
|
||||
sudo dnf install setzer
|
||||
```
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://fedoramagazine.org/4-cool-new-projects-to-try-in-copr-for-april-2020/
|
||||
|
||||
作者：[Dominik Turecek][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://fedoramagazine.org/author/dturecek/
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://fedoramagazine.org/wp-content/uploads/2017/08/4-copr-945x400.jpg
|
||||
[2]: https://copr.fedorainfracloud.org/
|
||||
[3]: https://docs.pagure.org/copr.copr/user_documentation.html#
|
||||
[4]: https://github.com/cjbassi/ytop
|
||||
[5]: https://fedoramagazine.org/wp-content/uploads/2020/04/ytop.png
|
||||
[6]: https://copr.fedorainfracloud.org/coprs/atim/ytop/
|
||||
[7]: https://fedoramagazine.org/howto-use-sudo/
|
||||
[8]: https://github.com/bcicen/ctop
|
||||
[9]: https://fedoramagazine.org/wp-content/uploads/2020/04/ctop.png
|
||||
[10]: https://copr.fedorainfracloud.org/coprs/fuhrmann/ctop/
|
||||
[11]: https://github.com/ranfdev/shortwave
|
||||
[12]: http://www.radio-browser.info/gui/#!/
|
||||
[13]: https://fedoramagazine.org/wp-content/uploads/2020/04/shortwave.png
|
||||
[14]: https://copr.fedorainfracloud.org/coprs/atim/shortwave/
|
||||
[15]: https://www.cvfosammmm.org/setzer/
|
||||
[16]: https://fedoramagazine.org/wp-content/uploads/2020/04/setzer.png
|
||||
[17]: https://copr.fedorainfracloud.org/coprs/lyessaadi/setzer/
|
||||
@ -0,0 +1,123 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (Create interactive learning games for kids with open source)
|
||||
[#]: via: (https://opensource.com/article/20/5/jclic-games-kids)
|
||||
[#]: author: (Peter Cheer https://opensource.com/users/petercheer)
|
||||
|
||||
Create interactive learning games for kids with open source
|
||||
======
|
||||
Help your students learn by creating fun puzzles and games in JClic, an
|
||||
easy Java-based app.
|
||||
![Family learning and reading together at night in a room][1]
|
||||
|
||||
Schools are closed in many countries around the world to slow the spread of COVID-19. This has suddenly thrown many parents and teachers into homeschooling. Fortunately, there are plenty of educational resources on the internet to use or adapt, although their licenses vary. You can try searching for Creative Commons Open Educational Resources, but if you want to create your own materials, there are many options for that to.
|
||||
|
||||
If you want to create digital educational activities with puzzles or tests, two easy-to-use, open source, cross-platform applications that fit the bill are eXeLearning and JClic. My earlier article on [eXeLearning][2] is a good introduction to that program, so here I'll look at [JClic][3]. It is an open source software project for creating various types of interactive activities such as associations, text-based activities, crosswords, and other puzzles with text, graphics, and multimedia elements.
|
||||
|
||||
Although it's been around since the 1990s, JClic never developed a large user base in the English-speaking world. It was created in Catalonia by the [Catalan Educational Telematic Network][4] (XTEC).
|
||||
|
||||
### About JClic
|
||||
|
||||
JClic is a Java-based application that's available in many Linux repositories and can be downloaded from [GitHub][5]. It runs on Linux, macOS, and Windows, but because it is a Java program, you must have a Java runtime environment [installed][6].
|
||||
|
||||
The program's interface has not really changed much over the years, even while features have been added or dropped, such as introducing HTML5 export functionality to replace Java Applet technology for web-based deployment. It hasn't needed to change much, though, because it's very effective at what it does.
|
||||
|
||||
### Creating a JClic project
|
||||
|
||||
Many teachers from many countries have used JClic to create interactive materials for a wide variety of ability levels, subjects, languages, and curricula. Some of these materials have been collected in an [downloadable activities library][7]. Although few activities are in English, you can get a sense of the possibilities JClic offers.
|
||||
|
||||
As JClic has a visual, point-and-click program interface, it is easy enough to learn that a new user can quickly concentrate on content creation. [Documentation][8] is available on GitHub.
|
||||
|
||||
The screenshots below are from one of the JClic projects I created to teach basic Excel skills to learners in Papua New Guinea.
|
||||
|
||||
A JClic project is created in its authoring tool and consists of the following four elements:
|
||||
|
||||
#### 1\. Metadata about the project
|
||||
|
||||
![JClic metadata][9]
|
||||
|
||||
#### 2\. A library of the graphical and other resources it uses
|
||||
|
||||
![JClic media][10]
|
||||
|
||||
#### 3\. A series of one or more activities
|
||||
|
||||
![JClic activities][11]
|
||||
|
||||
JClic can produce seven different activity types:
|
||||
|
||||
* Associations where the user discovers the relationships between two information sets
|
||||
* Memory games where the user discovers pairs of identical elements or relations (which are hidden) between them
|
||||
* Exploration activities involving the identification and information, based on a single Information set
|
||||
* Puzzles where the user reconstructs information that is initially presented in a disordered form; the activity can include graphics, text, sound, or a combination of them
|
||||
* Written-response activities that are solved by writing text, either a single word or a sentence
|
||||
* Text activities that are based on words, phrases, letters, and paragraphs of text that need to be completed, understood, corrected, or ordered; these activities can contain images and windows with active content
|
||||
* Word searches and crosswords
|
||||
|
||||
|
||||
|
||||
Because of variants in the activities, there are 16 possible activity types.
|
||||
|
||||
#### 4\. A timeline to sequence the activities
|
||||
|
||||
![JClic timeline][12]
|
||||
|
||||
### Using JClic content
|
||||
|
||||
Projects can run in JClic's player (part of the Java application you used to create the project), or they can be exported to HTML5 so they can run in a web browser.
|
||||
|
||||
The one thing I don't like about JClic is that its default HTML5 export function assumes you'll be online when running a project. If you want a project to work offline as needed, you must download a compiled and minified HTML5 player from [Github][13], and place it in the same folder as your JClic project.
|
||||
|
||||
Next, open the **index.html** file in a text editor and replace this line:
|
||||
|
||||
|
||||
```
|
||||
`<script type="text/javascript" src="https://clic.xtec.cat/dist/jclic.js/jclic.min.js"></script>`
|
||||
```
|
||||
|
||||
With:
|
||||
|
||||
|
||||
```
|
||||
`<script type="text/javascript" src="jclic.min.js"></script>`
|
||||
```
|
||||
|
||||
Now the HTML5 version of your project runs in a web browser, whether the user is online or not.
|
||||
|
||||
JClic also provides a reports function that can store test scores in an ODBC-compliant database. I have not explored this feature, as my tests and puzzles are mostly used for self-assessment and to prompt reflection by the learner, rather than as part of a formal scheme, so the scores are not very important. If you would like to learn about it, there is [documentation][14] on running JClic Reports Server with Tomcat and MySQL (or [mariaDB][15]).
|
||||
|
||||
### Conclusion
|
||||
|
||||
JClic offers a wide range of activity types that provide plenty of room to be creative in designing content to fit your subject area and type of learner. JClic is a valuable addition for anyone who needs a quick and easy way to develop educational resources.
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/20/5/jclic-games-kids
|
||||
|
||||
作者：[Peter Cheer][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/petercheer
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/family_learning_kids_night_reading.png?itok=6K7sJVb1 (Family learning and reading together at night in a room)
|
||||
[2]: https://opensource.com/article/18/5/exelearning
|
||||
[3]: https://clic.xtec.cat/legacy/en/jclic/index.html
|
||||
[4]: https://clic.xtec.cat/legacy/en/index.html
|
||||
[5]: https://github.com/projectestac/jclic
|
||||
[6]: https://adoptopenjdk.net/installation.html
|
||||
[7]: https://clic.xtec.cat/repo/
|
||||
[8]: https://github.com/projectestac/jclic/wiki/JClic_Guide
|
||||
[9]: https://opensource.com/sites/default/files/uploads/metadata.png (JClic metadata)
|
||||
[10]: https://opensource.com/sites/default/files/uploads/media.png (JClic media)
|
||||
[11]: https://opensource.com/sites/default/files/uploads/activities.png (JClic activities)
|
||||
[12]: https://opensource.com/sites/default/files/uploads/sequence.png (JClic timeline)
|
||||
[13]: http://projectestac.github.io/jclic.js/
|
||||
[14]: https://github.com/projectestac/jclic/wiki/Jclic-Reports-Server-with-Tomcat-and-MySQL-on-Ubuntu
|
||||
[15]: https://mariadb.org/
|
||||
@ -0,0 +1,150 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (Define and optimize data partitions in Apache Cassandra)
|
||||
[#]: via: (https://opensource.com/article/20/5/apache-cassandra)
|
||||
[#]: author: (Anil Inamdar https://opensource.com/users/anil-inamdar)
|
||||
|
||||
Define and optimize data partitions in Apache Cassandra
|
||||
======
|
||||
Apache Cassandra is built for speed and scalability; here's how to get
|
||||
the most out of those benefits.
|
||||
![Person standing in front of a giant computer screen with numbers, data][1]
|
||||
|
||||
Apache Cassandra is a database. But it's not just any database; it's a replicating database designed and tuned for scalability, high availability, low-latency, and performance. Cassandra can help your data survive regional outages, hardware failure, and what many admins would consider excessive amounts of data.
|
||||
|
||||
Having a thorough command of data partitions enables you to achieve superior Cassandra cluster design, performance, and scalability. In this article, I'll examine how to define partitions and how Cassandra uses them, as well as the most critical best practices and known issues you ought to be aware of.
|
||||
|
||||
To set the scene: partitions are chunks of data that serve as the atomic unit for key database-related functions like data distribution, replication, and indexing. Distributed data systems commonly distribute incoming data into these partitions, performing the partitioning with simple mathematical functions such as identity or hashing, and using a "partition key" to group data by partition. For example, consider a case where server logs arrive as incoming data. Using the "identity" partitioning function and the timestamps of each log (rounded to the hour value) for the partition key, we can partition this data such that each partition holds one hour of the logs.
|
||||
|
||||
### Data partitions in Cassandra
|
||||
|
||||
Cassandra operates as a distributed system and adheres to the data partitioning principles described above. With Cassandra, data partitioning relies on an algorithm configured at the cluster level, and a partition key configured at the table level.
|
||||
|
||||
![Cassandra data partition][2]
|
||||
|
||||
Cassandra Query Language (CQL) uses the familiar SQL table, row, and column terminologies. In the example diagram above, the table configuration includes the partition key within its primary key, with the format: Primary Key = Partition Key + [Clustering Columns].
|
||||
|
||||
A primary key in Cassandra represents both a unique data partition and a data arrangement inside a partition. Data arrangement information is provided by optional clustering columns. Each unique partition key represents a set of table rows managed in a server, as well as all servers that manage its replicas.
|
||||
|
||||
### Defining primary keys in CQL
|
||||
|
||||
The following four examples demonstrate how a primary key can be represented in CQL syntax. The sets of rows produced by these definitions are generally considered a partition.
|
||||
|
||||
#### Definition 1 (partition key: log_hour, clustering columns: none)
|
||||
|
||||
|
||||
```
|
||||
CREATE TABLE server_logs(
|
||||
log_hour TIMESTAMP PRIMARYKEY,
|
||||
log_level text,
|
||||
message text,
|
||||
server text
|
||||
)
|
||||
```
|
||||
|
||||
Here, all rows that share a **log_hour** go into the same partition.
|
||||
|
||||
#### Definition 2 (partition key: log_hour, clustering columns: log_level)
|
||||
|
||||
|
||||
```
|
||||
CREATE TABLE server_logs(
|
||||
log_hour TIMESTAMP,
|
||||
log_level text,
|
||||
message text,
|
||||
server text,
|
||||
PRIMARY KEY (log_hour, log_level)
|
||||
)
|
||||
```
|
||||
|
||||
This definition uses the same partition key as Definition 1, but here all rows in each partition are arranged in ascending order by **log_level**.
|
||||
|
||||
#### Definition 3 (partition key: log_hour, server, clustering columns: none)
|
||||
|
||||
|
||||
```
|
||||
CREATE TABLE server_logs(
|
||||
log_hour TIMESTAMP,
|
||||
log_level text,
|
||||
message text,
|
||||
server text,
|
||||
PRIMARY KEY ((log_hour, server))
|
||||
)
|
||||
```
|
||||
|
||||
In this definition, all rows share a **log_hour** for each distinct **server** as a single partition.
|
||||
|
||||
#### Definition 4 (partition key: log_hour, server, clustering columns: log_level)
|
||||
|
||||
|
||||
```
|
||||
CREATE TABLE server_logs(
|
||||
log_hour TIMESTAMP,
|
||||
log_level text,
|
||||
message text,
|
||||
server text,
|
||||
PRIMARY KEY ((log_hour, server),log_level)
|
||||
)WITH CLUSTERING ORDER BY (column3 DESC);
|
||||
```
|
||||
|
||||
This definition uses the same partition as Definition 3 but arranges the rows within a partition in descending order by **log_level**.
|
||||
|
||||
### How Cassandra uses the partition key
|
||||
|
||||
Cassandra relies on the partition key to determine which node to store data on and where to locate data when it's needed. Cassandra performs these read and write operations by looking at a partition key in a table, and using tokens (a long value out of range -2^63 to +2^63-1) for data distribution and indexing. These tokens are mapped to partition keys by using a partitioner, which applies a partitioning function that converts any partition key to a token. Through this token mechanism, every node of a Cassandra cluster owns a set of data partitions. The partition key then enables data indexing on each node.
|
||||
|
||||
![Cassandra cluster with 3 nodes and token-based ownership][3]
|
||||
|
||||
A Cassandra cluster with three nodes and token-based ownership. This is a simplistic representation: the actual implementation uses [Vnodes][4].
|
||||
|
||||
### Data partition impacts on Cassandra clusters
|
||||
|
||||
Careful partition key design is crucial to achieving the ideal partition size for the use case. Getting it right allows for even data distribution and strong I/O performance. Partition size has several impacts on Cassandra clusters you need to be aware of:
|
||||
|
||||
* Read performance—In order to find partitions in SSTables files on disk, Cassandra uses data structures that include caches, indexes, and index summaries. Partitions that are too large reduce the efficiency of maintaining these data structures – and will negatively impact performance as a result. Cassandra releases have made strides in this area: in particular, version 3.6 and above of the Cassandra engine introduce storage improvements that deliver better performance for large partitions and resilience against memory issues and crashes.
|
||||
* Memory usage— Large partitions place greater pressure on the JVM heap, increasing its size while also making the garbage collection mechanism less efficient.
|
||||
* Cassandra repairs—Large partitions make it more difficult for Cassandra to perform its repair maintenance operations, which keep data consistent by comparing data across replicas.
|
||||
* Tombstone eviction—Not as mean as it sounds, Cassandra uses unique markers known as "tombstones" to mark data for deletion. Large partitions can make that deletion process more difficult if there isn't an appropriate data deletion pattern and compaction strategy in place.
|
||||
|
||||
|
||||
|
||||
While these impacts may make it tempting to simply design partition keys that yield especially small partitions, the data access pattern is also highly influential on ideal partition size (for more information, read this in-depth guide to [Cassandra data modeling][5]). The data access pattern can be defined as how a table is queried, including all of the table's **select** queries. Ideally, CQL select queries should have just one partition key in the **where** clause—that is to say, Cassandra is most efficient when queries can get needed data from a single partition, instead of many smaller ones.
|
||||
|
||||
### Best practices for partition key design
|
||||
|
||||
Following best practices for partition key design helps you get to an ideal partition size. As a rule of thumb, the maximum partition size in Cassandra should stay under 100MB. Ideally, it should be under 10MB. While Cassandra versions 3.6 and newer make larger partition sizes more viable, careful testing and benchmarking must be performed for each workload to ensure a partition key design supports desired cluster performance.
|
||||
|
||||
Specifically, these best practices should be considered as part of any partition key design:
|
||||
|
||||
* The goal for a partition key must be to fit an ideal amount of data into each partition for supporting the needs of its access pattern.
|
||||
* A partition key should disallow unbounded partitions: those that may grow indefinitely in size over time. For instance, in the **server_logs** examples above, using the server column as a partition key would create unbounded partitions as the number of server logs continues to increase. In contrast, using **log_hour** limits each partition to an hour of data.
|
||||
* A partition key should also avoid creating a partition skew, in which partitions grow unevenly, and some are able to grow without limit over time. In the **server_logs** examples, using the server column in a scenario where one server generates considerably more logs than others would produce a partition skew. To avoid this, a useful technique is to introduce another attribute from the table to force an even distribution, even if it's necessary to create a dummy column to do so.
|
||||
* It's helpful to partition time-series data with a partition key that uses a time element as well as other attributes. This protects against unbounded partitions, enables access patterns to use the time attribute in querying specific data, and allows for time-bound data deletion. The examples above each demonstrate this by using the **log_hour** time attribute.
|
||||
|
||||
|
||||
|
||||
Several tools are available to help test, analyze, and monitor Cassandra partitions to check that a chosen schema is efficient and effective. By carefully designing partition keys to align well with the data and needs of the solution at hand, and following best practices to optimize partition size, you can utilize data partitions that more fully deliver on the scalability and performance potential of a Cassandra deployment.
|
||||
|
||||
Dani and Jon will give a three hour tutorial at OSCON this year called: Becoming friends with...
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/20/5/apache-cassandra
|
||||
|
||||
作者：[Anil Inamdar][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/anil-inamdar
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/data_metrics_analytics_desktop_laptop.png?itok=9QXd7AUr (Person standing in front of a giant computer screen with numbers, data)
|
||||
[2]: https://opensource.com/sites/default/files/uploads/apache_cassandra_1_0.png (Cassandra data partition)
|
||||
[3]: https://opensource.com/sites/default/files/uploads/apache_cassandra_2_0.png (Cassandra cluster with 3 nodes and token-based ownership)
|
||||
[4]: https://www.instaclustr.com/cassandra-vnodes-how-many-should-i-use/
|
||||
[5]: https://www.instaclustr.com/resource/6-step-guide-to-apache-cassandra-data-modelling-white-paper/
|
||||
@ -0,0 +1,445 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (Understanding systemd at startup on Linux)
|
||||
[#]: via: (https://opensource.com/article/20/5/systemd-startup)
|
||||
[#]: author: (David Both https://opensource.com/users/dboth)
|
||||
|
||||
Understanding systemd at startup on Linux
|
||||
======
|
||||
systemd's startup provides important clues to help you solve problems
|
||||
when they occur.
|
||||
![People at the start line of a race][1]
|
||||
|
||||
In [_Learning to love systemd_][2], the first article in this series, I looked at systemd's functions and architecture and the controversy around its role as a replacement for the old SystemV init program and startup scripts. In this second article, I'll start exploring the files and tools that manage the Linux startup sequence. I'll explain the systemd startup sequence, how to change the default startup target (runlevel in SystemV terms), and how to manually switch to a different target without going through a reboot.
|
||||
|
||||
I'll also look at two important systemd tools. The first is the **systemctl** command, which is the primary means of interacting with and sending commands to systemd. The second is **journalctl**, which provides access to the systemd journals that contain huge amounts of system history data such as kernel and service messages (both informational and error messages).
|
||||
|
||||
Be sure to use a non-production system for testing and experimentation in this and future articles. Your test system needs to have a GUI desktop (such as Xfce, LXDE, Gnome, KDE, or another) installed.
|
||||
|
||||
I wrote in my previous article that I planned to look at creating a systemd unit and adding it to the startup sequence in this article. Because this article became longer than I anticipated, I will hold that for the next article in this series.
|
||||
|
||||
### Exploring Linux startup with systemd
|
||||
|
||||
Before you can observe the startup sequence, you need to do a couple of things to make the boot and startup sequences open and visible. Normally, most distributions use a startup animation or splash screen to hide the detailed messages that would otherwise be displayed during a Linux host's startup and shutdown. This is called the Plymouth boot screen on Red Hat-based distros. Those hidden messages can provide a great deal of information about startup and shutdown to a sysadmin looking for information to troubleshoot a bug or to just learn about the startup sequence. You can change this using the GRUB (Grand Unified Boot Loader) configuration.
|
||||
|
||||
The main GRUB configuration file is **/boot/grub2/grub.cfg**, but, because this file can be overwritten when the kernel version is updated, you do not want to change it. Instead, modify the **/etc/default/grub** file, which is used to modify the default settings of **grub.cfg**.
|
||||
|
||||
Start by looking at the current, unmodified version of the **/etc/default/grub** file:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 ~]# cd /etc/default ; cat grub
|
||||
GRUB_TIMEOUT=5
|
||||
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
|
||||
GRUB_DEFAULT=saved
|
||||
GRUB_DISABLE_SUBMENU=true
|
||||
GRUB_TERMINAL_OUTPUT="console"
|
||||
GRUB_CMDLINE_LINUX="resume=/dev/mapper/fedora_testvm1-swap rd.lvm.
|
||||
lv=fedora_testvm1/root rd.lvm.lv=fedora_testvm1/swap rd.lvm.lv=fedora_
|
||||
testvm1/usr rhgb quiet"
|
||||
GRUB_DISABLE_RECOVERY="true"
|
||||
[root@testvm1 default]#
|
||||
```
|
||||
|
||||
Chapter 6 of the [GRUB documentation][3] contains a list of all the possible entries in the **/etc/default/grub** file, but I focus on the following:
|
||||
|
||||
* I change **GRUB_TIMEOUT**, the number of seconds for the GRUB menu countdown, from five to 10 to give a bit more time to respond to the GRUB menu before the countdown hits zero.
|
||||
* I delete the last two parameters on **GRUB_CMDLINE_LINUX**, which lists the command-line parameters that are passed to the kernel at boot time. One of these parameters, **rhgb** stands for Red Hat Graphical Boot, and it displays the little Fedora icon animation during the kernel initialization instead of showing boot-time messages. The other, the **quiet** parameter, prevents displaying the startup messages that document the progress of the startup and any errors that occur. I delete both **rhgb** and **quiet** because sysadmins need to see these messages. If something goes wrong during boot, the messages displayed on the screen can point to the cause of the problem.
|
||||
|
||||
|
||||
|
||||
After you make these changes, your GRUB file will look like:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 default]# cat grub
|
||||
GRUB_TIMEOUT=10
|
||||
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
|
||||
GRUB_DEFAULT=saved
|
||||
GRUB_DISABLE_SUBMENU=true
|
||||
GRUB_TERMINAL_OUTPUT="console"
|
||||
GRUB_CMDLINE_LINUX="resume=/dev/mapper/fedora_testvm1-swap rd.lvm.
|
||||
lv=fedora_testvm1/root rd.lvm.lv=fedora_testvm1/swap rd.lvm.lv=fedora_
|
||||
testvm1/usr"
|
||||
GRUB_DISABLE_RECOVERY="false"
|
||||
[root@testvm1 default]#
|
||||
```
|
||||
|
||||
The **grub2-mkconfig** program generates the **grub.cfg** configuration file using the contents of the **/etc/default/grub** file to modify some of the default GRUB settings. The **grub2-mkconfig** program sends its output to **STDOUT**. It has a **-o** option that allows you to specify a file to send the datastream to, but it is just as easy to use redirection. Run the following command to update the **/boot/grub2/grub.cfg** configuration file:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 grub2]# grub2-mkconfig > /boot/grub2/grub.cfg
|
||||
Generating grub configuration file ...
|
||||
Found linux image: /boot/vmlinuz-4.18.9-200.fc28.x86_64
|
||||
Found initrd image: /boot/initramfs-4.18.9-200.fc28.x86_64.img
|
||||
Found linux image: /boot/vmlinuz-4.17.14-202.fc28.x86_64
|
||||
Found initrd image: /boot/initramfs-4.17.14-202.fc28.x86_64.img
|
||||
Found linux image: /boot/vmlinuz-4.16.3-301.fc28.x86_64
|
||||
Found initrd image: /boot/initramfs-4.16.3-301.fc28.x86_64.img
|
||||
Found linux image: /boot/vmlinuz-0-rescue-7f12524278bd40e9b10a085bc82dc504
|
||||
Found initrd image: /boot/initramfs-0-rescue-7f12524278bd40e9b10a085bc82dc504.img
|
||||
done
|
||||
[root@testvm1 grub2]#
|
||||
```
|
||||
|
||||
Reboot your test system to view the startup messages that would otherwise be hidden behind the Plymouth boot animation. But what if you need to view the startup messages and have not disabled the Plymouth boot animation? Or you have, but the messages stream by too fast to read? (Which they do.)
|
||||
|
||||
There are a couple of options, and both involve log files and systemd journals—which are your friends. You can use the **less** command to view the contents of the **/var/log/messages** file. This file contains boot and startup messages as well as messages generated by the operating system during normal operation. You can also use the **journalctl** command without any options to view the systemd journal, which contains essentially the same information:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 grub2]# journalctl
|
||||
\-- Logs begin at Sat 2020-01-11 21:48:08 EST, end at Fri 2020-04-03 08:54:30 EDT. --
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: Linux version 5.3.7-301.fc31.x86_64 ([mockbuild@bkernel03.phx2.fedoraproject.org][4]) (gcc version 9.2.1 20190827 (Red Hat 9.2.1-1) (GCC)) #1 SMP Mon Oct >
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: Command line: BOOT_IMAGE=(hd0,msdos1)/vmlinuz-5.3.7-301.fc31.x86_64 root=/dev/mapper/VG01-root ro resume=/dev/mapper/VG01-swap rd.lvm.lv=VG01/root rd>
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers'
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers'
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers'
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: x86/fpu: xstate_offset[2]: 576, xstate_sizes[2]: 256
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: x86/fpu: Enabled xstate features 0x7, context size is 832 bytes, using 'standard' format.
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-provided physical RAM map:
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-e820: [mem 0x0000000000100000-0x00000000dffeffff] usable
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-e820: [mem 0x00000000dfff0000-0x00000000dfffffff] ACPI data
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-e820: [mem 0x00000000fec00000-0x00000000fec00fff] reserved
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-e820: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: BIOS-e820: [mem 0x0000000100000000-0x000000041fffffff] usable
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: NX (Execute Disable) protection: active
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: SMBIOS 2.5 present.
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: DMI: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: Hypervisor detected: KVM
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: kvm-clock: Using msrs 4b564d01 and 4b564d00
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: kvm-clock: cpu 0, msr 30ae01001, primary cpu clock
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: kvm-clock: using sched offset of 8250734066 cycles
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: clocksource: kvm-clock: mask: 0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: tsc: Detected 2807.992 MHz processor
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
|
||||
Jan 11 21:48:08 f31vm.both.org kernel: e820: remove [mem 0x000a0000-0x000fffff] usable
|
||||
<snip>
|
||||
```
|
||||
|
||||
I truncated this datastream because it can be hundreds of thousands or even millions of lines long. (The journal listing on my primary workstation is 1,188,482 lines long.) Be sure to try this on your test system. If it has been running for some time—even if it has been rebooted many times—huge amounts of data will be displayed. Explore this journal data because it contains a lot of information that can be very useful when doing problem determination. Knowing what this data looks like for a normal boot and startup can help you locate problems when they occur.
|
||||
|
||||
I will discuss systemd journals, the **journalctl** command, and how to sort through all of that data to find what you want in more detail in a future article in this series.
|
||||
|
||||
After GRUB loads the kernel into memory, it must first extract itself from the compressed version of the file before it can perform any useful work. After the kernel has extracted itself and started running, it loads systemd and turns control over to it.
|
||||
|
||||
This is the end of the boot process. At this point, the Linux kernel and systemd are running but unable to perform any productive tasks for the end user because nothing else is running, there's no shell to provide a command line, no background processes to manage the network or other communication links, and nothing that enables the computer to perform any productive function.
|
||||
|
||||
Systemd can now load the functional units required to bring the system up to a selected target run state.
|
||||
|
||||
### Targets
|
||||
|
||||
A systemd target represents a Linux system's current or desired run state. Much like SystemV start scripts, targets define the services that must be present for the system to run and be active in that state. Figure 1 shows the possible run-state targets of a Linux system using systemd. As seen in the first article of this series and in the systemd bootup man page (man bootup), there are other intermediate targets that are required to enable various necessary services. These can include **swap.target**, **timers.target**, **local-fs.target**, and more. Some targets (like **basic.target**) are used as checkpoints to ensure that all the required services are up and running before moving on to the next-higher level target.
|
||||
|
||||
Unless otherwise changed at boot time in the GRUB menu, systemd always starts the **default.target**. The **default.target** file is a symbolic link to the true target file. For a desktop workstation, this is typically going to be the **graphical.target**, which is equivalent to runlevel 5 in SystemV. For a server, the default is more likely to be the **multi-user.target**, which is like runlevel 3 in SystemV. The **emergency.target** file is similar to single-user mode. Targets and services are systemd units.
|
||||
|
||||
The following table, which I included in the previous article in this series, compares the systemd targets with the old SystemV startup runlevels. The systemd target aliases are provided by systemd for backward compatibility. The target aliases allow scripts—and sysadmins—to use SystemV commands like **init 3** to change runlevels. Of course, the SystemV commands are forwarded to systemd for interpretation and execution.
|
||||
|
||||
**systemd targets** | **SystemV runlevel** | **target aliases** | **Description**
|
||||
---|---|---|---
|
||||
default.target | | | This target is always aliased with a symbolic link to either **multi-user.target** or **graphical.target**. systemd always uses the **default.target** to start the system. The **default.target** should never be aliased to **halt.target**, **poweroff.target**, or **reboot.target**.
|
||||
graphical.target | 5 | runlevel5.target | **Multi-user.target** with a GUI
|
||||
| 4 | runlevel4.target | Unused. Runlevel 4 was identical to runlevel 3 in the SystemV world. This target could be created and customized to start local services without changing the default **multi-user.target**.
|
||||
multi-user.target | 3 | runlevel3.target | All services running, but command-line interface (CLI) only
|
||||
| 2 | runlevel2.target | Multi-user, without NFS, but all other non-GUI services running
|
||||
rescue.target | 1 | runlevel1.target | A basic system, including mounting the filesystems with only the most basic services running and a rescue shell on the main console
|
||||
emergency.target | S | | Single-user mode—no services are running; filesystems are not mounted. This is the most basic level of operation with only an emergency shell running on the main console for the user to interact with the system.
|
||||
halt.target | | | Halts the system without powering it down
|
||||
reboot.target | 6 | runlevel6.target | Reboot
|
||||
poweroff.target | 0 | runlevel0.target | Halts the system and turns the power off
|
||||
|
||||
Each target has a set of dependencies described in its configuration file. systemd starts the required dependencies, which are the services required to run the Linux host at a specific level of functionality. When all of the dependencies listed in the target configuration files are loaded and running, the system is running at that target level. If you want, you can review the systemd startup sequence and runtime targets in the first article in this series, [_Learning to love systemd_][2].
|
||||
|
||||
### Exploring the current target
|
||||
|
||||
Many Linux distributions default to installing a GUI desktop interface so that the installed systems can be used as workstations. I always install from a Fedora Live boot USB drive with an Xfce or LXDE desktop. Even when I'm installing a server or other infrastructure type of host (such as the ones I use for routers and firewalls), I use one of these installations that installs a GUI desktop.
|
||||
|
||||
I could install a server without a desktop (and that would be typical for data centers), but that does not meet my needs. It is not that I need the GUI desktop itself, but the LXDE installation includes many of the other tools I use that are not in a default server installation. This means less work for me after the initial installation.
|
||||
|
||||
But just because I have a GUI desktop does not mean it makes sense to use it. I have a 16-port KVM that I can use to access the KVM interfaces of most of my Linux systems, but the vast majority of my interaction with them is via a remote SSH connection from my primary workstation. This way is more secure and uses fewer system resources to run **multi-user.target** compared to **graphical.target.**
|
||||
|
||||
To begin, check the default target to verify that it is the **graphical.target**:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 ~]# systemctl get-default
|
||||
graphical.target
|
||||
[root@testvm1 ~]#
|
||||
```
|
||||
|
||||
Now verify the currently running target. It should be the same as the default target. You can still use the old method, which displays the old SystemV runlevels. Note that the previous runlevel is on the left; it is **N** (which means None), indicating that the runlevel has not changed since the host was booted. The number 5 indicates the current target, as defined in the old SystemV terminology:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 ~]# runlevel
|
||||
N 5
|
||||
[root@testvm1 ~]#
|
||||
```
|
||||
|
||||
Note that the runlevel man page indicates that runlevels are obsolete and provides a conversion table.
|
||||
|
||||
You can also use the systemd method. There is no one-line answer here, but it does provide the answer in systemd terms:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 ~]# systemctl list-units --type target
|
||||
UNIT LOAD ACTIVE SUB DESCRIPTION
|
||||
basic.target loaded active active Basic System
|
||||
cryptsetup.target loaded active active Local Encrypted Volumes
|
||||
getty.target loaded active active Login Prompts
|
||||
graphical.target loaded active active Graphical Interface
|
||||
local-fs-pre.target loaded active active Local File Systems (Pre)
|
||||
local-fs.target loaded active active Local File Systems
|
||||
multi-user.target loaded active active Multi-User System
|
||||
network-online.target loaded active active Network is Online
|
||||
network.target loaded active active Network
|
||||
nfs-client.target loaded active active NFS client services
|
||||
nss-user-lookup.target loaded active active User and Group Name Lookups
|
||||
paths.target loaded active active Paths
|
||||
remote-fs-pre.target loaded active active Remote File Systems (Pre)
|
||||
remote-fs.target loaded active active Remote File Systems
|
||||
rpc_pipefs.target loaded active active rpc_pipefs.target
|
||||
slices.target loaded active active Slices
|
||||
sockets.target loaded active active Sockets
|
||||
sshd-keygen.target loaded active active sshd-keygen.target
|
||||
swap.target loaded active active Swap
|
||||
sysinit.target loaded active active System Initialization
|
||||
timers.target loaded active active Timers
|
||||
|
||||
LOAD = Reflects whether the unit definition was properly loaded.
|
||||
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
|
||||
SUB = The low-level unit activation state, values depend on unit type.
|
||||
|
||||
21 loaded units listed. Pass --all to see loaded but inactive units, too.
|
||||
To show all installed unit files use 'systemctl list-unit-files'.
|
||||
```
|
||||
|
||||
This shows all of the currently loaded and active targets. You can also see the **graphical.target** and the **multi-user.target**. The **multi-user.target** is required before the **graphical.target** can be loaded. In this example, the **graphical.target** is active.
|
||||
|
||||
### Switching to a different target
|
||||
|
||||
Making the switch to the **multi-user.target** is easy:
|
||||
|
||||
|
||||
```
|
||||
`[root@testvm1 ~]# systemctl isolate multi-user.target`
|
||||
```
|
||||
|
||||
The display should now change from the GUI desktop or login screen to a virtual console. Log in and list the currently active systemd units to verify that **graphical.target** is no longer running:
|
||||
|
||||
|
||||
```
|
||||
`[root@testvm1 ~]# systemctl list-units --type target`
|
||||
```
|
||||
|
||||
Be sure to use the **runlevel** command to verify that it shows both previous and current "runlevels":
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 ~]# runlevel
|
||||
5 3
|
||||
```
|
||||
|
||||
### Changing the default target
|
||||
|
||||
Now, change the default target to the **multi-user.target** so that it will always boot into the **multi-user.target** for a console command-line interface rather than a GUI desktop interface. As the root user on your test host, change to the directory where the systemd configuration is maintained and do a quick listing:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 ~]# cd /etc/systemd/system/ ; ll
|
||||
drwxr-xr-x. 2 root root 4096 Apr 25 2018 basic.target.wants
|
||||
<snip>
|
||||
lrwxrwxrwx. 1 root root 36 Aug 13 16:23 default.target -> /lib/systemd/system/graphical.target
|
||||
lrwxrwxrwx. 1 root root 39 Apr 25 2018 display-manager.service -> /usr/lib/systemd/system/lightdm.service
|
||||
drwxr-xr-x. 2 root root 4096 Apr 25 2018 getty.target.wants
|
||||
drwxr-xr-x. 2 root root 4096 Aug 18 10:16 graphical.target.wants
|
||||
drwxr-xr-x. 2 root root 4096 Apr 25 2018 local-fs.target.wants
|
||||
drwxr-xr-x. 2 root root 4096 Oct 30 16:54 multi-user.target.wants
|
||||
<snip>
|
||||
[root@testvm1 system]#
|
||||
```
|
||||
|
||||
I shortened this listing to highlight a few important things that will help explain how systemd manages the boot process. You should be able to see the entire list of directories and links on your virtual machine.
|
||||
|
||||
The **default.target** entry is a symbolic link (symlink, soft link) to the directory **/lib/systemd/system/graphical.target**. List that directory to see what else is there:
|
||||
|
||||
|
||||
```
|
||||
`[root@testvm1 system]# ll /lib/systemd/system/ | less`
|
||||
```
|
||||
|
||||
You should see files, directories, and more links in this listing, but look specifically for **multi-user.target** and **graphical.target**. Now display the contents of **default.target**, which is a link to **/lib/systemd/system/graphical.target**:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 system]# cat default.target
|
||||
# SPDX-License-Identifier: LGPL-2.1+
|
||||
#
|
||||
# This file is part of systemd.
|
||||
#
|
||||
# systemd is free software; you can redistribute it and/or modify it
|
||||
# under the terms of the GNU Lesser General Public License as published by
|
||||
# the Free Software Foundation; either version 2.1 of the License, or
|
||||
# (at your option) any later version.
|
||||
|
||||
[Unit]
|
||||
Description=Graphical Interface
|
||||
Documentation=man:systemd.special(7)
|
||||
Requires=multi-user.target
|
||||
Wants=display-manager.service
|
||||
Conflicts=rescue.service rescue.target
|
||||
After=multi-user.target rescue.service rescue.target display-manager.service
|
||||
AllowIsolate=yes
|
||||
[root@testvm1 system]#
|
||||
```
|
||||
|
||||
This link to the **graphical.target** file describes all of the prerequisites and requirements that the graphical user interface requires. I will explore at least some of these options in the next article in this series.
|
||||
|
||||
To enable the host to boot to multi-user mode, you need to delete the existing link and create a new one that points to the correct target. Make the [PWD][5] **/etc/systemd/system**, if it is not already:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 system]# rm -f default.target
|
||||
[root@testvm1 system]# ln -s /lib/systemd/system/multi-user.target default.target
|
||||
```
|
||||
|
||||
List the **default.target** link to verify that it links to the correct file:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 system]# ll default.target
|
||||
lrwxrwxrwx 1 root root 37 Nov 28 16:08 default.target -> /lib/systemd/system/multi-user.target
|
||||
[root@testvm1 system]#
|
||||
```
|
||||
|
||||
If your link does not look exactly like this, delete it and try again. List the content of the **default.target** link:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 system]# cat default.target
|
||||
# SPDX-License-Identifier: LGPL-2.1+
|
||||
#
|
||||
# This file is part of systemd.
|
||||
#
|
||||
# systemd is free software; you can redistribute it and/or modify it
|
||||
# under the terms of the GNU Lesser General Public License as published by
|
||||
# the Free Software Foundation; either version 2.1 of the License, or
|
||||
# (at your option) any later version.
|
||||
|
||||
[Unit]
|
||||
Description=Multi-User System
|
||||
Documentation=man:systemd.special(7)
|
||||
Requires=basic.target
|
||||
Conflicts=rescue.service rescue.target
|
||||
After=basic.target rescue.service rescue.target
|
||||
AllowIsolate=yes
|
||||
[root@testvm1 system]#
|
||||
```
|
||||
|
||||
The **default.target**—which is really a link to the **multi-user.target** at this point—now has different requirements in the **[Unit]** section. It does not require the graphical display manager.
|
||||
|
||||
Reboot. Your virtual machine should boot to the console login for virtual console 1, which is identified on the display as tty1. Now that you know how to change the default target, change it back to the **graphical.target** using a command designed for the purpose.
|
||||
|
||||
First, check the current default target:
|
||||
|
||||
|
||||
```
|
||||
[root@testvm1 ~]# systemctl get-default
|
||||
multi-user.target
|
||||
[root@testvm1 ~]# systemctl set-default graphical.target
|
||||
Removed /etc/systemd/system/default.target.
|
||||
Created symlink /etc/systemd/system/default.target → /usr/lib/systemd/system/graphical.target.
|
||||
[root@testvm1 ~]#
|
||||
```
|
||||
|
||||
Enter the following command to go directly to the **graphical.target** and the display manager login page without having to reboot:
|
||||
|
||||
|
||||
```
|
||||
`[root@testvm1 system]# systemctl isolate default.target`
|
||||
```
|
||||
|
||||
I do not know why the term "isolate" was chosen for this sub-command by systemd's developers. My research indicates that it may refer to running the specified target but "isolating" and terminating all other targets that are not required to support the target. However, the effect is to switch targets from one run target to another—in this case, from the multi-user target to the graphical target. The command above is equivalent to the old init 5 command in SystemV start scripts and the init program.
|
||||
|
||||
Log into the GUI desktop, and verify that it is working as it should.
|
||||
|
||||
### Summing up
|
||||
|
||||
This article explored the Linux systemd startup sequence and started to explore two important systemd tools, **systemctl** and **journalctl**. It also explained how to switch from one target to another and to change the default target.
|
||||
|
||||
The next article in this series will create a new systemd unit and configure it to run during startup. It will also look at some of the configuration options that help determine where in the sequence a particular unit will start, for example, after networking is up and running.
|
||||
|
||||
### Resources
|
||||
|
||||
There is a great deal of information about systemd available on the internet, but much is terse, obtuse, or even misleading. In addition to the resources mentioned in this article, the following webpages offer more detailed and reliable information about systemd startup.
|
||||
|
||||
* The Fedora Project has a good, practical [guide][6] [to systemd][6]. It has pretty much everything you need to know in order to configure, manage, and maintain a Fedora computer using systemd.
|
||||
* The Fedora Project also has a good [cheat sheet][7] that cross-references the old SystemV commands to comparable systemd ones.
|
||||
* For detailed technical information about systemd and the reasons for creating it, check out [Freedesktop.org][8]'s [description of systemd][9].
|
||||
* [Linux.com][10]'s "More systemd fun" offers more advanced systemd [information and tips][11].
|
||||
|
||||
|
||||
|
||||
There is also a series of deeply technical articles for Linux sysadmins by Lennart Poettering, the designer and primary developer of systemd. These articles were written between April 2010 and September 2011, but they are just as relevant now as they were then. Much of everything else good that has been written about systemd and its ecosystem is based on these papers.
|
||||
|
||||
* [Rethinking PID 1][12]
|
||||
* [systemd for Administrators, Part I][13]
|
||||
* [systemd for Administrators, Part II][14]
|
||||
* [systemd for Administrators, Part III][15]
|
||||
* [systemd for Administrators, Part IV][16]
|
||||
* [systemd for Administrators, Part V][17]
|
||||
* [systemd for Administrators, Part VI][18]
|
||||
* [systemd for Administrators, Part VII][19]
|
||||
* [systemd for Administrators, Part VIII][20]
|
||||
* [systemd for Administrators, Part IX][21]
|
||||
* [systemd for Administrators, Part X][22]
|
||||
* [systemd for Administrators, Part XI][23]
|
||||
|
||||
|
||||
|
||||
Alison Chiaken, a Linux kernel and systems programmer at Mentor Graphics, offers a preview of her...
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/20/5/systemd-startup
|
||||
|
||||
作者：[David Both][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/dboth
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/start_line.jpg?itok=9reaaW6m (People at the start line of a race)
|
||||
[2]: https://opensource.com/article/20/4/systemd
|
||||
[3]: http://www.gnu.org/software/grub/manual/grub
|
||||
[4]: mailto:mockbuild@bkernel03.phx2.fedoraproject.org
|
||||
[5]: https://en.wikipedia.org/wiki/Pwd
|
||||
[6]: https://docs.fedoraproject.org/en-US/quick-docs/understanding-and-administering-systemd/index.html
|
||||
[7]: https://fedoraproject.org/wiki/SysVinit_to_Systemd_Cheatsheet
|
||||
[8]: http://Freedesktop.org
|
||||
[9]: http://www.freedesktop.org/wiki/Software/systemd
|
||||
[10]: http://Linux.com
|
||||
[11]: https://www.linux.com/training-tutorials/more-systemd-fun-blame-game-and-stopping-services-prejudice/
|
||||
[12]: http://0pointer.de/blog/projects/systemd.html
|
||||
[13]: http://0pointer.de/blog/projects/systemd-for-admins-1.html
|
||||
[14]: http://0pointer.de/blog/projects/systemd-for-admins-2.html
|
||||
[15]: http://0pointer.de/blog/projects/systemd-for-admins-3.html
|
||||
[16]: http://0pointer.de/blog/projects/systemd-for-admins-4.html
|
||||
[17]: http://0pointer.de/blog/projects/three-levels-of-off.html
|
||||
[18]: http://0pointer.de/blog/projects/changing-roots
|
||||
[19]: http://0pointer.de/blog/projects/blame-game.html
|
||||
[20]: http://0pointer.de/blog/projects/the-new-configuration-files.html
|
||||
[21]: http://0pointer.de/blog/projects/on-etc-sysinit.html
|
||||
[22]: http://0pointer.de/blog/projects/instances.html
|
||||
[23]: http://0pointer.de/blog/projects/inetd.html
|
||||
@ -0,0 +1,124 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (Browse the Peer-to-peer Web With Beaker Browser)
|
||||
[#]: via: (https://itsfoss.com/beaker-browser/)
|
||||
[#]: author: (John Paul https://itsfoss.com/author/john/)
|
||||
|
||||
Browse the Peer-to-peer Web With Beaker Browser
|
||||
======
|
||||
|
||||
The Internet as we know it has existed unchanged (more or less) for the last 50 years. People across the globe use their devices to retrieve data from huge servers dotted around the world.
|
||||
|
||||
A group of dedicated technologists wants to change that to make the internet a place where people can connect and share information directly instead of relying on a central server (decentralization).
|
||||
|
||||
There are a bunch of such decentralized services that we have already covered on It’s FOSS. [LBRY as YouTube alternative][1], [Mastodon as Twitter alternative][2] are just a couple of such examples.
|
||||
|
||||
And today I am going to cover another such product called [Beaker Browser][3] which is essentially for browsing the peer to peer web.
|
||||
|
||||
![Beaker Browser][4]
|
||||
|
||||
### What is the ‘peer-to-peer Web’?
|
||||
|
||||
According to [one of the devs][5] behind the Beaker browser, “The P2P Web is an experimental set of technologies…to give users more control over the Web.”
|
||||
|
||||
Further, they say that the peer-to-peer Web has three main principles: anybody can be a server; multiple computers can serve the same site; there is no back end.
|
||||
|
||||
As you can see from those principles. the idea of the peer-to-peer Web is very similar to BitTorrent where files are seeded by multiple peers and those peers share the bandwidth load. This reduces the overall bandwidth that a person needs to provide for their site.
|
||||
|
||||
![Beaker Browser Settings][6]
|
||||
|
||||
The other major part of the peer-to-peer Web is creator control of their ideas. In this day and age, platforms being controlled by large corporations, who try to use your data for their benefit. Beaker returns control to the content creators.
|
||||
|
||||
### Browsing the decentralized web with Beaker
|
||||
|
||||
The [Beaker Browser][3] first came into existence in 2016. The project (and the technology that surrounds it) is created by a team of three at [Blue Link Labs][7]. The Beaker Browser uses the [Dat protocol][8] to share data between computers. All websites that use the Dat protocol start with `dat://` instead of `http://`.
|
||||
|
||||
The strengths of the Dat protocol are:
|
||||
|
||||
* Fast – Archives sync from multiple sources at once.
|
||||
* Secure – All updates are signed and integrity-checked.
|
||||
* Resilient – Archives can change hosts without changing their URLs.
|
||||
* Versioned – Changes are written to an append-only version log.
|
||||
* Decentralized – Any device can host any archive.
|
||||
|
||||
|
||||
|
||||
![Beaker Browser Seeding][9]
|
||||
|
||||
The Beaker Browser is essentially a cut down version of Chromium with built-in support for `dat://`addresses. It can still visit regular `http://` sites.
|
||||
|
||||
Each time you visit a dat site, the content for that site is downloaded to your computer as you request it. For example, a picture of Linux Torvalds on the about page of a site is not downloaded until you navigate to that page.
|
||||
|
||||
Also, once you visit a dat website, “[you temporarily][10] re-upload or seed whichever files you’ve downloaded from the website.” You can also choose to seed the website to help its creator.
|
||||
|
||||
![Beaker Browser Menu][11]
|
||||
|
||||
Since the whole idea of Beaker is to create a more open web, you can easily view the source of any website. Unlike most browsers where you just see the source code the current page, you are viewing, Beaker shows you the entire structure of the site in a GitHub-like view. You can even fork the site and host your version of it.
|
||||
|
||||
Besides visiting dat-based websites, you can also create your own site. In the Beaker Browser menu, there is an option to create a new website or an empty project. If you select the option to create a new website, Beaker will build a little demo site that you can edit with the browser’s built-in editor.
|
||||
|
||||
However, if you are like me and prefer to use Markdown, you can choose to create an empty project. Beaker will create the structure of a site and assign it a `dat://`address. Create an `index.md` file and you are good to go. There is a [short tutorial][12] with more info. You can also use the create empty project option to build a web app.
|
||||
|
||||
![Beaker Browser Website Template][13]
|
||||
|
||||
Since Beaker acts as a web server and site seeder, any time you close it or turn off your computer your site will become unavailable. Thankfully, you don’t have to run your computer or the browser constantly. You can also use a seeding service named [Hashbase][14] or you can set up a [`homebase`][15] seeding server.
|
||||
|
||||
Though Beaker is [available][16] for Linux, Windows, and macOS. If you do start playing around Beaker, be sure to take a quick look at [their gui][17][d][17][es][17].
|
||||
|
||||
### Beaker Browser is not for everyone but it has a purpose
|
||||
|
||||
When I first got this assignment, I had high hopes for the Beaker Browser. As it stands now, it’s still very experimental. A number of the dat sites that I tried to visit were unavailable because the user was not seeding their site. Beaker does have an option to notify you when that site is back online.
|
||||
|
||||
![Beaker Browser No Peer][18]
|
||||
|
||||
Another problem is that Beaker is a really stripped down version of Chromium. There is no option to install extensions or themes. Instead, you are stuck with a white theme and a very limited toolset. I would not use this as my main browser and having access to the world of dat websites is not enough of a reason to keep it installed on my system.
|
||||
|
||||
I looked to see if there is an extension for Firefox that would add support for the `dat://` protocol. I did find such an extension, but it also required the installation of a couple of other pieces of software. It’s just easier to install Beaker.
|
||||
|
||||
As it stands now, Beaker is not for me. Maybe in the future, more people will start using Beaker or the dat protocol will gain support by other browsers. Then it might be interesting. Right now, it’s kinda empty.
|
||||
|
||||
As part of my time with Beaker, I created a [website][19] using the built-in tools. Don’t worry, I made sure that it’s seeded.
|
||||
|
||||
![Beaker Bowser Site Source][20]
|
||||
|
||||
What are your thoughts on the Beaker Brower? What are your thoughts on the peer-to-peer web? Please let us know in the comments below.
|
||||
|
||||
If you found this article interesting, please take a minute to share it on social media, Hacker News, or [Reddit][21].
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://itsfoss.com/beaker-browser/
|
||||
|
||||
作者：[John Paul][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://itsfoss.com/author/john/
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://itsfoss.com/lbry/
|
||||
[2]: https://itsfoss.com/mastodon-open-source-alternative-twitter/
|
||||
[3]: https://beakerbrowser.com/
|
||||
[4]: https://i2.wp.com/itsfoss.com/wp-content/uploads/2020/04/beaker-browser.jpg?resize=800%2C426&ssl=1
|
||||
[5]: https://pfrazee.hashbase.io/blog/what-is-the-p2p-web
|
||||
[6]: https://i0.wp.com/itsfoss.com/wp-content/uploads/2020/04/beaker-bowser-setting.jpg?resize=800%2C573&ssl=1
|
||||
[7]: https://bluelinklabs.com/
|
||||
[8]: https://www.datprotocol.com/
|
||||
[9]: https://i0.wp.com/itsfoss.com/wp-content/uploads/2020/04/beaker-bowser-seedding.jpg?resize=800%2C466&ssl=1
|
||||
[10]: https://beakerbrowser.com/docs/faq/
|
||||
[11]: https://i1.wp.com/itsfoss.com/wp-content/uploads/2020/04/beaker-browser-menu.jpg?ssl=1
|
||||
[12]: https://beakerbrowser.com/docs/guides/create-a-markdown-site
|
||||
[13]: https://i1.wp.com/itsfoss.com/wp-content/uploads/2020/04/beaker-browser-website-template.jpg?resize=800%2C459&ssl=1
|
||||
[14]: https://hashbase.io/
|
||||
[15]: https://github.com/beakerbrowser/homebase
|
||||
[16]: https://beakerbrowser.com/install/
|
||||
[17]: https://beakerbrowser.com/docs/guides/
|
||||
[18]: https://i0.wp.com/itsfoss.com/wp-content/uploads/2020/04/beaker-browser-no-peer.jpg?resize=800%2C424&ssl=1
|
||||
[19]: https://41bfbd06731e8d9c5d5676e8145069c69b254e7a3b710ddda4f6e9804529690c/
|
||||
[20]: https://i2.wp.com/itsfoss.com/wp-content/uploads/2020/04/beaker-bowser-source.jpg?resize=800%2C544&ssl=1
|
||||
[21]: https://reddit.com/r/linuxusersgroup
|
||||
@ -0,0 +1,143 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: (lxbwolf)
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (Drop PNG and JPG for your online images: Use WebP)
|
||||
[#]: via: (https://opensource.com/article/20/4/webp-image-compression)
|
||||
[#]: author: (Jeff Macharyas https://opensource.com/users/jeffmacharyas)
|
||||
|
||||
线上图片请抛弃 PNG 和 JPG 后缀：使用 WebP
|
||||
======
|
||||
了解一下这个开源的图片编辑工具来节省时间和空间。
|
||||
![Painting art on a computer screen][1]
|
||||
|
||||
WebP 是 2010 年 Google 开发的一种图片格式，能提供对网络图片的无损压缩和有损压缩。网络开发者们可以使用 WebP 来创建更小更丰富的图片，以此来提高网站的速度。更快的加载速度对于网站的用户体验和网站市场的效能是至关重要的。
|
||||
|
||||
为了提供领先于所有的设备和用户的图片加载能力，你网站上的图片文件大小不应该超过 500 KB。
|
||||
|
||||
WebP 无损图片通常比 PNG 图片文件小至少 25%。在相同的 SSIM（structural similarity，结构相似性）质量指标下，WebP 有损图片通常比 JPEG 图片小 25% 到 34%。
|
||||
|
||||
无损 WebP 也支持透明度。在有损 RGB 压缩可接受的情况下，有损 WebP 也支持透明度，PNG 文件的大小通常为 WebP 文件大小的四倍。
|
||||
|
||||
Google 报告把动图 GIF 文件转换为有损 WebP后文件大小减少了 64%，转换为无损 WebP 后文件大小减少了 19%。
|
||||
|
||||
WebP 文件格式是一种基于 RIFF（resource interchange file format，资源交换文件格式）的文档格式。你可以用 [hexdump][2] 看到文件的签名是 **52 49 46 46** (RIFF)：
|
||||
|
||||
|
||||
```
|
||||
$ hexdump --canonical pixel.webp
|
||||
00000000 52 49 46 46 26 00 00 00 [...] |RIFF&...WEBPVP8 |
|
||||
00000010 1a 00 00 00 30 01 00 9d [...] |....0....*......|
|
||||
00000020 0e 25 a4 00 03 70 00 fe [...] |.%...p...`....|
|
||||
0000002e
|
||||
```
|
||||
|
||||
独立的 libwebp 库以 WebP 技术规范的引用实现的方式提供服务，可以从 Google 的 [Git 仓库][3] 或下载 tar 包获得。
|
||||
|
||||
全球在用的 80% 的 web 浏览器兼容 WebP 格式。本文撰写时，Apple 的 Safari 浏览器还不兼容。对于不兼容的情况，应变方法是在 WebP 图片旁边准备一张 JPG/PNG 图片，我们有很多种方法和 Wordpress 插件来实现。
|
||||
|
||||
### 为什么这很重要？
|
||||
|
||||
我的部分工作是设计和维护我们组织的网站。由于网站是个市场工具并且网站速度是衡量用户体验的重要指标，我一直致力于提高网站速度，通过把图片转换为 WebP 来减少图片大小是一个有效的解决方案。
|
||||
|
||||
我使用了 **web.dev** 来检测其中一个网页，该工具是由 Lighthouse 提供服务的，遵循 Apache 2.0 证书，可以在 <https://github.com/GoogleChrome/lighthouse> 找到。
|
||||
|
||||
根据官方描述，”LIghthouse 是一个开源的，旨在提升网页质量的自动化工具。你可以在任何网页上运行它 — 公共的或需要鉴权的。它有性能、可用性、积极的 web 应用、SEO和其他项目的审计。你可以使用命令行、作为一个 Node 模块或在 Chrome DevTools 里运行 Lighthouse。你输入一个 URL 给 Lighthouse，它对这个网页运行一系列的审计规则，之后生成这个网页的审计结果报告。从报告的失败审计条目中可以知道应该怎么优化网页。每条审计都有对应的文档解释为什么该项目是重要的，以及如何修复它。“
|
||||
|
||||
### 创建更小的 WebP 图片
|
||||
|
||||
我测试的页面返回了三张图片。在它生成的报告中，它提供了推荐和目标格式。我选择了它报告有 650 KB 的 ”app-graphic“ 图片。通过把它转换为 WebP 格式，预计可以图片大小降到 61 KB，节省 589 KB。我在 Photoshop 中把它转换了，用默认的 WebP 设置参数保存它，它的文件大小为 44.9 KB。比预期的还要好！从下面的 Photoshop 截图中可以看出，两张图在视觉上完全一样。
|
||||
|
||||
![WebP vs JPG comparison][4]
|
||||
|
||||
左图：650 KB（实际大小）。右图： 589 KB（转换之后的目标大小）。
|
||||
|
||||
当然，也可以用开源图片编辑工具 [GIMP][5] 把图片导出为 WebP。它提供了几个质量和压缩的参数：
|
||||
|
||||
![GIMP dialog for exporting webp, as a webp][6]
|
||||
|
||||
另一张图拉近视野后：
|
||||
|
||||
![WebP vs PNG comparison][7]
|
||||
|
||||
PNG（左图）和 WebP（右图），都是从 JPG 转换而来，两图对比可以看出 WebP 不仅在文件大小更小，在视觉质量上也更优秀。
|
||||
|
||||
### 把图片转换为 WebP
|
||||
|
||||
你也可以用 Linux 的命令行工具把图片从 JPG/PNG 转换为 WebP：
|
||||
|
||||
在命令行使用 **cwebp** 把 PNG 或 JPG 图片文件转换为 WebP 格式。你可以用下面的命令把 PNG 图片文件转换为质量参数为 80 的 WebP 图片。
|
||||
|
||||
|
||||
```
|
||||
`cwebp -q 80 image.png -o image.webp`
|
||||
```
|
||||
|
||||
你还可以用 [Image Magick][8]，这个工具可能在你的发行版本软件仓库中可以找到。转换的子命令是 **convert**，它需要的所有参数就是输入和输出文件：
|
||||
|
||||
|
||||
```
|
||||
`convert pixel.png pixel.webp`
|
||||
```
|
||||
|
||||
### 使用编辑器把图片转换为 WebP
|
||||
|
||||
使用 [GIMP][9] 图片编辑器来把图片转换为 WebP。从 2.10 版本开始，它原生地支持 WebP。
|
||||
|
||||
如果你是 Photoshop 用户，由于 Photoshop 默认不包含 WebP，因此你需要一个转换插件。遵循 Apache License 2.0 证书发行的 WebPShop 0.2.1 是一个用户打开和保存包括动图在内的 WebP 图片的 Photoshop 模块，在 <https://github.com/webmproject/WebPShop> 可以找到。
|
||||
|
||||
为了能正常使用它，你需要把它放进 Photoshop 插件目录下的 **bin** 文件夹：
|
||||
|
||||
Windows x64—C:\Program Files\Adobe\Adobe Photoshop\Plug-ins\WebPShop.8bi
|
||||
|
||||
Mac—Applications/Adobe Photoshop/Plug-ins/WebPShop.plugin
|
||||
|
||||
### Wordpress 上的 WebP
|
||||
|
||||
很多网站是用 Wordpress 搭建的（我的网站就是）。因此，Wordpress 怎么上传 WebP 图片？本文撰写时，它还不支持。但是，当然已经有插件来满足这种需求，因此你可以在你的网站上同时准备 WebP 和 PNG/JPG 图片（为 Apple 用户）。
|
||||
|
||||
在 [Marius Hosting][11] 有下面的指示：
|
||||
|
||||
”直接向 Wordpress 上传 WebP 图片会怎样？这很简单。向你的主题 functions.php 文件添加几行内容就可以了。Wordpress 默认不支持展示和上传 WebP 文件，但是我会向你陈述怎么通过几个简单的步骤来让它支持。登录进你的 Wordpress 管理员界面，进入 Appearance/Theme Editor 找到 functions.php。拷贝下面的代码粘贴到文件最后并保存。
|
||||
|
||||
|
||||
```
|
||||
`//** *Enable upload for webp image files.*/ function webp_upload_mimes($existing_mimes) { $existing_mimes['webp'] = 'image/webp'; return $existing_mimes; } add_filter('mime_types', 'webp_upload_mimes');`
|
||||
```
|
||||
|
||||
"如果你想在 Media/Library 看缩略图预览，那么你需要把下面的代码也添加到 functions.php 文件。为了找到 functions.php 文件，进入 Appearance/Theme Editor 并搜索 functions.php，然后拷贝下面的代码粘贴到文件最后并保存。“
|
||||
|
||||
|
||||
```
|
||||
`//** * Enable preview / thumbnail for webp image files.*/ function webp_is_displayable($result, $path) { if ($result === false) { $displayable_image_types = array( IMAGETYPE_WEBP ); $info = @getimagesize( $path ); if (empty($info)) { $result = false; } elseif (!in_array($info[2], $displayable_image_types)) { $result = false; } else { $result = true; } } return $result; } add_filter('file_is_displayable_image', 'webp_is_displayable', 10, 2);`
|
||||
```
|
||||
|
||||
### WebP 和未来
|
||||
|
||||
WebP 是鲁棒的和最优的格式。它看起来更好，有更好的压缩率，它拥有其他大部分常见图片格式的所有特性。不必再等了，现在就使用它把。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/20/4/webp-image-compression
|
||||
|
||||
作者：[Jeff Macharyas][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[lxbwolf](https://github.com/lxbwolf)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/jeffmacharyas
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/painting_computer_screen_art_design_creative.png?itok=LVAeQx3_ (Painting art on a computer screen)
|
||||
[2]: https://opensource.com/article/19/8/dig-binary-files-hexdump
|
||||
[3]: https://storage.googleapis.com/downloads.webmproject.org/releases/webp/index.html
|
||||
[4]: https://opensource.com/sites/default/files/uploads/webp-vs-jpg-app-graphic.png (WebP vs JPG comparison)
|
||||
[5]: http://gimp.org
|
||||
[6]: https://opensource.com/sites/default/files/webp-gimp.webp (GIMP dialog for exporting webp, as a webp)
|
||||
[7]: https://opensource.com/sites/default/files/uploads/xcompare-png-left-webp-right.png (WebP vs PNG comparison)
|
||||
[8]: https://imagemagick.org
|
||||
[9]: https://en.wikipedia.org/wiki/GIMP
|
||||
[10]: https://mariushosting.com/how-to-upload-webp-files-on-wordpress/
|
||||
[11]: https://mariushosting.com/
|
||||
Loading…
Reference in New Issue
Block a user