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@ -0,0 +1,100 @@
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||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: (oska874)
|
||||
[#]: reviewer: (wxy)
|
||||
[#]: publisher: (wxy)
|
||||
[#]: url: (https://linux.cn/article-10530-1.html)
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||||
[#]: subject: (Computer Laboratory – Raspberry Pi: Lesson 5 OK05)
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||||
[#]: via: (https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/ok05.html)
|
||||
[#]: author: (Robert Mullins http://www.cl.cam.ac.uk/~rdm34)
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||||
|
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计算机实验室之树莓派：课程 5 OK05
|
||||
======
|
||||
|
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OK05 课程构建于课程 OK04 的基础，使用它来闪烁摩尔斯电码的 SOS 序列（`...---...`）。这里假设你已经有了 [课程 4：OK04][1] 操作系统的代码作为基础。
|
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|
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### 1、数据
|
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|
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到目前为止，我们与操作系统有关的所有内容提供的都是指令。然而有时候，指令只是完成了一半的工作。我们的操作系统可能还需要数据。
|
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|
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> 一些早期的操作系统确实只允许特定文件中的特定类型的数据，但是这通常被认为限制太多了。现代方法确实可以使程序变得复杂的多。
|
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|
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通常，数据就是些很重要的值。你可能接受过培训，认为数据就是某种类型的，比如，文本文件包含文本，图像文件包含图片，等等。说实话，这只是你的想法而已。计算机上的全部数据都是二进制数字，重要的是我们选择用什么来解释这些数据。在这个例子中，我们会用一个闪灯序列作为数据保存下来。
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在 `main.s` 结束处复制下面的代码：
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|
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```
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.section .data %定义 .data 段
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.align 2 %对齐
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pattern: %定义整形变量
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.int 0b11111111101010100010001000101010
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```
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> `.align num` 确保下一行代码的地址是 2^num 的整数倍。
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> `.int val` 输出数值 `val`。
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|
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要区分数据和代码，我们将数据都放在 `.data` 区域。我已经将该区域包含在操作系统的内存布局图。我选择将数据放到代码后面。将我们的指令和数据分开保存的原因是，如果最后我们在自己的操作系统上实现一些安全措施，我们就需要知道代码的那些部分是可以执行的，而那些部分是不行的。
|
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|
||||
我在这里使用了两个新命令 `.align` 和 `.int`。`.align` 保证接下来的数据是按照 2 的乘方对齐的。在这个里，我使用 `.align 2` ，意味着数据最终存放的地址是 2^2=4 的整数倍。这个操作是很重要的，因为我们用来读取内存的指令 `ldr` 要求内存地址是 4 的倍数。
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命令 `.int` 直接复制它后面的常量到输出。这意味着 11111111101010100010001000101010<sub>2</sub> 将会被存放到输出，所以该标签模式实际是将这段数据标识为模式。
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> 关于数据的一个挑战是寻找一个高效和有用的展示形式。这种保存一个开、关的时间单元的序列的方式，运行起来很容易，但是将很难编辑，因为摩尔斯电码的 `-` 或 `.` 样式丢失了。
|
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|
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如我提到的，数据可以代表你想要的所有东西。在这里我编码了摩尔斯电码的 SOS 序列，对于不熟悉的人，就是 `...---...`。我使用 0 表示一个时间单元的 LED 灭灯，而 1 表示一个时间单元的 LED 亮。这样，我们可以像这样编写一些代码在数据中显示一个序列，然后要显示不同序列，我们所有需要做的就是修改这段数据。下面是一个非常简单的例子，操作系统必须一直执行这段程序，解释和展示数据。
|
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|
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复制下面几行到 `main.s` 中的标记 `loop$` 之前。
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```
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ptrn .req r4 %重命名 r4 为 ptrn
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ldr ptrn,=pattern %加载 pattern 的地址到 ptrn
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ldr ptrn,[ptrn] %加载地址 ptrn 所在内存的值
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seq .req r5 %重命名 r5 为 seq
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mov seq,#0 %seq 赋值为 0
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```
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这段代码加载 `pattrern` 到寄存器 `r4`，并加载 0 到寄存器 `r5`。`r5` 将是我们的序列位置，所以我们可以追踪我们已经展示了多少个 `pattern`。
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如果 `pattern` 的当前位置是 1 且仅有一个 1，下面的代码将非零值放入 `r1`。
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|
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```
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mov r1,#1 %加载1到 r1
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lsl r1,seq %对r1 的值逻辑左移 seq 次
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and r1,ptrn %按位与
|
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```
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这段代码对你调用 `SetGpio` 很有用，它必须有一个非零值来关掉 LED，而一个 0 值会打开 LED。
|
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|
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现在修改 `main.s` 中你的全部代码，这样代码中每次循环会根据当前的序列数设置 LED，等待 250000 毫秒（或者其他合适的延时），然后增加序列数。当这个序列数到达 32 就需要返回 0。看看你是否能实现这个功能，作为额外的挑战，也可以试着只使用一条指令。
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|
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### 2、当你玩得开心时，时间过得很快
|
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|
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你现在准备好在树莓派上实验。应该闪烁一串包含 3 个短脉冲，3 个长脉冲，然后 3 个短脉冲的序列。在一次延时之后，这种模式应该重复。如果这不工作，请查看我们的问题页。
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|
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一旦它工作，祝贺你已经抵达 OK 系列教程的结束点。
|
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|
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在这个系列我们学习了汇编代码，GPIO 控制器和系统定时器。我们已经学习了函数和 ABI，以及几个基础的操作系统原理，已经关于数据的知识。
|
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|
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你现在已经可以准备学习下面几个更高级的课程的某一个。
|
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|
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* [Screen][2] 系列是接下来的，会教你如何通过汇编代码使用屏幕。
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* [Input][3] 系列教授你如何使用键盘和鼠标。
|
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|
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到现在，你已经有了足够的信息来制作操作系统，用其它方法和 GPIO 交互。如果你有任何机器人工具，你可能会想尝试编写一个通过 GPIO 管脚控制的机器人操作系统。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/ok05.html
|
||||
|
||||
作者：[Robert Mullins][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[ezio](https://github.com/oska874)
|
||||
校对：[wxy](https://github.com/wxy)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: http://www.cl.cam.ac.uk/~rdm34
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://linux.cn/article-10526-1.html
|
||||
[2]: https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/screen01.html
|
||||
[3]: https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/input01.html
|
||||
@ -1,14 +1,15 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: (HankChow)
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: reviewer: (wxy)
|
||||
[#]: publisher: (wxy)
|
||||
[#]: url: (https://linux.cn/article-10529-1.html)
|
||||
[#]: subject: (More About Angle Brackets in Bash)
|
||||
[#]: via: (https://www.linux.com/blog/learn/2019/1/more-about-angle-brackets-bash)
|
||||
[#]: author: (Paul Brown https://www.linux.com/users/bro66)
|
||||
|
||||
Bash 中尖括号的更多用法
|
||||
======
|
||||
> 在这篇文章，我们继续来深入探讨尖括号的更多其它用法。
|
||||
|
||||
|
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|
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@ -22,19 +23,20 @@ Bash 中尖括号的更多用法
|
||||
diff <(ls /original/dir/) <(ls /backup/dir/)
|
||||
```
|
||||
|
||||
[`diff`][2] 命令是一个逐行比较两个文件之间差异的工具。在上面的例子中，就使用了 `<` 让 `diff` 认为两个 `ls` 命令输出的结果都是文件，从而能够比较它们之间的差异。
|
||||
[diff][2] 命令是一个逐行比较两个文件之间差异的工具。在上面的例子中，就使用了 `<` 让 `diff` 认为两个 `ls` 命令输出的结果都是文件，从而能够比较它们之间的差异。
|
||||
|
||||
要注意，在 `<` 和 `(...)` 之间是没有空格的。
|
||||
|
||||
我尝试在我的图片目录和它的备份目录执行上面的命令，输出的是以下结果：
|
||||
|
||||
```
|
||||
diff <(ls /My/Pictures/) <(ls /My/backup/Pictures/) 5d4 < Dv7bIIeUUAAD1Fc.jpg:large.jpg
|
||||
diff <(ls /My/Pictures/) <(ls /My/backup/Pictures/)
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||||
5d4 < Dv7bIIeUUAAD1Fc.jpg:large.jpg
|
||||
```
|
||||
|
||||
输出结果中的 `<` 表示 `Dv7bIIeUUAAD1Fc.jpg:large.jpg` 这个文件存在于左边的目录（`/My/Pictures`）但不存在于右边的目录（`/My/backup/Pictures`）中。也就是说，在备份过程中可能发生了问题，导致这个文件没有被成功备份。如果 `diff` 没有显示出任何输出结果，就表明两个目录中的文件是一致的。
|
||||
|
||||
看到这里你可能会想到，既然可以通过 `<` 将一些命令行的输出内容作为一个文件，提供给一个需要接受文件格式的命令，那么在上一篇文章的“最喜欢的演员排序”例子中，就可以省去中间的一些步骤，直接对输出内容执行 `sort` 操作了。
|
||||
看到这里你可能会想到，既然可以通过 `<` 将一些命令行的输出内容作为一个文件提供给一个需要接受文件格式的命令，那么在上一篇文章的“最喜欢的演员排序”例子中，就可以省去中间的一些步骤，直接对输出内容执行 `sort` 操作了。
|
||||
|
||||
确实如此，这个例子可以简化成这样：
|
||||
|
||||
@ -42,7 +44,7 @@ diff <(ls /My/Pictures/) <(ls /My/backup/Pictures/) 5d4 < Dv7bIIeUUAAD1Fc.jpg:la
|
||||
sort -r <(while read -r name surname films;do echo $films $name $surname ; done < CBactors)
|
||||
```
|
||||
|
||||
### Here string
|
||||
### Here 字符串
|
||||
|
||||
除此以外，尖括号的重定向功能还有另一种使用方式。
|
||||
|
||||
@ -52,9 +54,9 @@ sort -r <(while read -r name surname films;do echo $films $name $surname ; done
|
||||
myvar="Hello World" echo $myvar | tr '[:lower:]' '[:upper:]' HELLO WORLD
|
||||
```
|
||||
|
||||
[`tr`][3] 命令可以将一个字符串转换为某种格式。在上面的例子中，就使用了 `tr` 将字符串中的所有小写字母都转换为大写字母。
|
||||
[tr][3] 命令可以将一个字符串转换为某种格式。在上面的例子中，就使用了 `tr` 将字符串中的所有小写字母都转换为大写字母。
|
||||
|
||||
要理解的是，这个传递过程的重点不是变量，而是变量的值，也就是字符串 `Hello World`。这样的字符串叫做 here string，含义是“这就是我们要处理的字符串”。但对于上面的例子，还可以用更直观的方式的处理，就像下面这样：
|
||||
要理解的是，这个传递过程的重点不是变量，而是变量的值，也就是字符串 `Hello World`。这样的字符串叫做 HERE 字符串，含义是“这就是我们要处理的字符串”。但对于上面的例子，还可以用更直观的方式的处理，就像下面这样：
|
||||
|
||||
```
|
||||
tr '[:lower:]' '[:upper:]' <<< $myvar
|
||||
@ -75,13 +77,13 @@ via: https://www.linux.com/blog/learn/2019/1/more-about-angle-brackets-bash
|
||||
作者：[Paul Brown][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[HankChow](https://github.com/HankChow)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
校对：[wxy](https://github.com/wxy)
|
||||
|
||||
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://www.linux.com/users/bro66
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://www.linux.com/blog/learn/2019/1/understanding-angle-brackets-bash
|
||||
[1]: https://linux.cn/article-10502-1.html
|
||||
[2]: https://linux.die.net/man/1/diff
|
||||
[3]: https://linux.die.net/man/1/tr
|
||||
|
||||
@ -0,0 +1,69 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (Introducing kids to computational thinking with Python)
|
||||
[#]: via: (https://opensource.com/article/19/2/break-down-stereotypes-python)
|
||||
[#]: author: (Don Watkins https://opensource.com/users/don-watkins)
|
||||
|
||||
Introducing kids to computational thinking with Python
|
||||
======
|
||||
Coding program gives low-income students the skills, confidence, and knowledge to break free from economic and societal disadvantages.
|
||||
|
||||
|
||||
|
||||
When the [Parkman Branch][1] of the Detroit Public Library was flooded with bored children taking up all the computers during summer break, the library saw it not as a problem, rather an opportunity. They started a coding club, the [Parkman Coders][2], led by [Qumisha Goss][3], a librarian who is leveraging the power of Python to introduce disadvantaged children to computational thinking.
|
||||
|
||||
When she started the Parkman Coders program about four years ago, "Q" (as she is known) didn't know much about coding. Since then, she's become a specialist in library instruction and technology and a certified Raspberry Pi instructor.
|
||||
|
||||
The program began by using [Scratch][4], but the students got bored with the block coding interface, which they regarded as "baby stuff." She says, "I knew we need to make a change to something that was still beginner friendly, but that would be more challenging for them to continue to hold their attention." At this point, she started teaching them Python.
|
||||
|
||||
Q first saw Python while playing a game with dungeons and skeleton monsters on [Code.org][5]. She began to learn Python by reading books like [Python Programming: An Introduction to Computer Science][6] and [Python for Kids][7]. She also recommends [Automate the Boring Stuff with Python][8] and [Lauren Ipsum: A Story about Computer Science and Other Improbable Things][9].
|
||||
|
||||
### Setting up a Raspberry Pi makerspace
|
||||
|
||||
Q decided to use [Raspberry Pi][10] computers to avoid the possibility that the students might be able to hack into the library system's computers, which weren't arranged in a way conducive to a makerspace anyway. The Pi's affordability, plus its flexibility and the included free software, lent more credibility to her decision.
|
||||
|
||||
While the coder program was the library's effort keep the peace and create a learning space that would engage the children, it quickly grew so popular that it ran out of space, computers, and adequate electrical outlets in a building built in 1921. They started with 10 Raspberry Pi computers shared among 20 children, but the library obtained funding from individuals, companies including Microsoft, the 4H, and the Detroit Public Library Foundation to get more equipment and expand the program.
|
||||
|
||||
Currently, about 40 children participate in each session and they have enough Raspberry Pi's for one device per child and some to give away. Many of the Parkman Coders come from low socio-economic backgrounds and don't have a computer at home, so the library provides them with donated Chromebooks.
|
||||
|
||||
Q says, "when kids demonstrate that they have a good understanding of how to use a Raspberry Pi or a [Microbit][11] and have been coming to programs regularly, we give them equipment to take home with them. This process is very challenging, however, because [they may not] have internet access at home [or] all the peripheral things they need like monitors, keyboards, and mice."
|
||||
|
||||
### Learning life skills and breaking stereotypes with Python
|
||||
|
||||
Q says, "I believe that the mainstays of learning computer science are learning critical thinking and problem-solving skills. My hope is that these lessons will stay with the kids as they grow and pursue futures in whatever field they choose. In addition, I'm hoping to inspire some pride in creatorship. It's a very powerful feeling to know 'I made this thing,' and once they've had these successes early, I hope they will approach new challenges with zeal."
|
||||
|
||||
She also says, "in learning to program, you have to learn to be hyper-vigilant about spelling and capitalization, and for some of our kids, reading is an issue. To make sure that the program is inclusive, we spell aloud during our lessons, and we encourage kids to speak up if they don't know a word or can't spell it correctly."
|
||||
|
||||
Q also tries to give extra attention to children who need it. She says, "if I recognize that someone has a more severe problem, we try to get them paired with a tutor at our library outside of program time, but still allow them to come to the program. We want to help them without discouraging them from participating."
|
||||
|
||||
Most importantly, the Parkman Coders program seeks to help every child realize that each has a unique skill set and abilities. Most of the children are African-American and half are girls. Q says, "we live in a world where we grow up with societal stigmas that frequently limit our own belief of what we can accomplish." She believes that children need a nonjudgmental space where "they can try new things, mess up, and discover."
|
||||
|
||||
The environment Q and the Parkman Coders program creates helps the participants break away from economic and societal disadvantages. She says that the secret sauce is to "make sure you have a welcoming space so anyone can come and that your space is forgiving and understanding. Let people come as they are, and be prepared to teach and to learn; when people feel comfortable and engaged, they want to stay."
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/19/2/break-down-stereotypes-python
|
||||
|
||||
作者：[Don Watkins][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/don-watkins
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://detroitpubliclibrary.org/locations/parkman
|
||||
[2]: https://www.dplfound.org/single-post/2016/05/15/Parkman-Branch-Coders
|
||||
[3]: https://www.linkedin.com/in/qumisha-goss-b3bb5470
|
||||
[4]: https://scratch.mit.edu/
|
||||
[5]: http://Code.org
|
||||
[6]: https://www.amazon.com/Python-Programming-Introduction-Computer-Science/dp/1887902996
|
||||
[7]: https://nostarch.com/pythonforkids
|
||||
[8]: https://automatetheboringstuff.com/
|
||||
[9]: https://nostarch.com/laurenipsum
|
||||
[10]: https://www.raspberrypi.org/
|
||||
[11]: https://microbit.org/guide/
|
||||
@ -1,5 +1,5 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: translator: (Guevaraya)
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
|
||||
172
sources/tech/20190205 5 Streaming Audio Players for Linux.md
Normal file
172
sources/tech/20190205 5 Streaming Audio Players for Linux.md
Normal file
@ -0,0 +1,172 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (5 Streaming Audio Players for Linux)
|
||||
[#]: via: (https://www.linux.com/blog/2019/2/5-streaming-audio-players-linux)
|
||||
[#]: author: (Jack Wallen https://www.linux.com/users/jlwallen)
|
||||
|
||||
5 Streaming Audio Players for Linux
|
||||
======
|
||||
|
||||
|
||||
As I work, throughout the day, music is always playing in the background. Most often, that music is in the form of vinyl spinning on a turntable. But when I’m not in purist mode, I’ll opt to listen to audio by way of a streaming app. Naturally, I’m on the Linux platform, so the only tools I have at my disposal are those that play well on my operating system of choice. Fortunately, plenty of options exist for those who want to stream audio to their Linux desktops.
|
||||
|
||||
In fact, Linux offers a number of solid offerings for music streaming, and I’ll highlight five of my favorite tools for this task. A word of warning, not all of these players are open source. But if you’re okay running a proprietary app on your open source desktop, you have some really powerful options. Let’s take a look at what’s available.
|
||||
|
||||
### Spotify
|
||||
|
||||
Spotify for Linux isn’t some dumb-downed, half-baked app that crashes every other time you open it, and doesn’t offer the full-range of features found on the macOS and Windows equivalent. In fact, the Linux version of Spotify is exactly the same as you’ll find on other platforms. With the Spotify streaming client you can listen to music and podcasts, create playlists, discover new artists, and so much more. And the Spotify interface (Figure 1) is quite easy to navigate and use.
|
||||
|
||||
![Spotify][2]
|
||||
|
||||
Figure 1: The Spotify interface makes it easy to find new music and old favorites.
|
||||
|
||||
[Used with permission][3]
|
||||
|
||||
You can install Spotify either using snap (with the command sudo snap install spotify), or from the official repository, with the following commands:
|
||||
|
||||
* sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 931FF8E79F0876134EDDBDCCA87FF9DF48BF1C90
|
||||
|
||||
* sudo echo deb <http://repository.spotify.com> stable non-free | sudo tee /etc/apt/sources.list.d/spotify.list
|
||||
|
||||
* sudo apt-get update
|
||||
|
||||
* sudo apt-get install spotify-client
|
||||
|
||||
|
||||
|
||||
|
||||
Once installed, you’ll want to log into your Spotify account, so you can start streaming all of the great music to help motivate you to get your work done. If you have Spotify installed on other devices (and logged into the same account), you can dictate to which device the music should stream (by clicking the Devices Available icon near the bottom right corner of the Spotify window).
|
||||
|
||||
### Clementine
|
||||
|
||||
Clementine one of the best music players available to the Linux platform. Clementine not only allows user to play locally stored music, but to connect to numerous streaming audio services, such as:
|
||||
|
||||
* Amazon Cloud Drive
|
||||
|
||||
* Box
|
||||
|
||||
* Dropbox
|
||||
|
||||
* Icecast
|
||||
|
||||
* Jamendo
|
||||
|
||||
* Magnatune
|
||||
|
||||
* RockRadio.com
|
||||
|
||||
* Radiotunes.com
|
||||
|
||||
* SomaFM
|
||||
|
||||
* SoundCloud
|
||||
|
||||
* Spotify
|
||||
|
||||
* Subsonic
|
||||
|
||||
* Vk.com
|
||||
|
||||
* Or internet radio streams
|
||||
|
||||
|
||||
|
||||
|
||||
There are two caveats to using Clementine. The first is you must be using the most recent version (as the build available in some repositories is out of date and won’t install the necessary streaming plugins). Second, even with the most recent build, some streaming services won’t function as expected. For example, with Spotify, you’ll only have available to you the Top Tracks (and not your playlist … or the ability to search for songs).
|
||||
|
||||
With Clementine Internet radio streaming, you’ll find musicians and bands you’ve never heard of (Figure 2), and plenty of them to tune into.
|
||||
|
||||
![Clementine][5]
|
||||
|
||||
Figure 2: Clementine Internet radio is a great way to find new music.
|
||||
|
||||
[Used with permission][3]
|
||||
|
||||
### Odio
|
||||
|
||||
Odio is a cross-platform, proprietary app (available for Linux, MacOS, and Windows) that allows you to stream internet music stations of all genres. Radio stations are curated from [www.radio-browser.info][6] and the app itself does an incredible job of presenting the streams for you (Figure 3).
|
||||
|
||||
|
||||
![Odio][8]
|
||||
|
||||
Figure 3: The Odio interface is one of the best you’ll find.
|
||||
|
||||
[Used with permission][3]
|
||||
|
||||
Odio makes it very easy to find unique Internet radio stations and even add those you find and enjoy to your library. Currently, the only way to install Odio on Linux is via Snap. If your distribution supports snap packages, install this streaming app with the command:
|
||||
|
||||
sudo snap install odio
|
||||
|
||||
Once installed, you can open the app and start using it. There is no need to log into (or create) an account. Odio is very limited in its settings. In fact, it only offers the choice between a dark or light theme in the settings window. However, as limited as it might be, Odio is one of your best bets for playing Internet radio on Linux.
|
||||
|
||||
Streamtuner2 is an outstanding Internet radio station GUI tool. With it you can stream music from the likes of:
|
||||
|
||||
* Internet radio stations
|
||||
|
||||
* Jameno
|
||||
|
||||
* MyOggRadio
|
||||
|
||||
* Shoutcast.com
|
||||
|
||||
* SurfMusic
|
||||
|
||||
* TuneIn
|
||||
|
||||
* Xiph.org
|
||||
|
||||
* YouTube
|
||||
|
||||
|
||||
### StreamTuner2
|
||||
|
||||
Streamtuner2 offers a nice (if not slightly outdated) interface, that makes it quite easy to find and stream your favorite music. The one caveat with StreamTuner2 is that it’s really just a GUI for finding the streams you want to hear. When you find a station, double-click on it to open the app associated with the stream. That means you must have the necessary apps installed, in order for the streams to play. If you don’t have the proper apps, you can’t play the streams. Because of this, you’ll spend a good amount of time figuring out what apps to install for certain streams (Figure 4).
|
||||
|
||||
![Streamtuner2][10]
|
||||
|
||||
Figure 4: Configuring Streamtuner2 isn’t for the faint of heart.
|
||||
|
||||
[Used with permission][3]
|
||||
|
||||
### VLC
|
||||
|
||||
VLC has been, for a very long time, dubbed the best media playback tool for Linux. That’s with good reason, as it can play just about anything you throw at it. Included in that list is streaming radio stations. Although you won’t find VLC connecting to the likes of Spotify, you can head over to Internet-Radio, click on a playlist and have VLC open it without a problem. And considering how many internet radio stations are available at the moment, you won’t have any problem finding music to suit your tastes. VLC also includes tools like visualizers, equalizers (Figure 5), and more.
|
||||
|
||||
![VLC ][12]
|
||||
|
||||
Figure 5: The VLC visualizer and equalizer features in action.
|
||||
|
||||
[Used with permission][3]
|
||||
|
||||
The only caveat to VLC is that you do have to have a URL for the Internet Radio you wish you hear, as the tool itself doesn’t curate. But with those links in hand, you won’t find a better media player than VLC.
|
||||
|
||||
### Always More Where That Came From
|
||||
|
||||
If one of these five tools doesn’t fit your needs, I suggest you open your distribution’s app store and search for one that will. There are plenty of tools to make streaming music, podcasts, and more not only possible on Linux, but easy.
|
||||
|
||||
Learn more about Linux through the free ["Introduction to Linux" ][13] course from The Linux Foundation and edX.
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://www.linux.com/blog/2019/2/5-streaming-audio-players-linux
|
||||
|
||||
作者：[Jack Wallen][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://www.linux.com/users/jlwallen
|
||||
[b]: https://github.com/lujun9972
|
||||
[2]: https://www.linux.com/sites/lcom/files/styles/rendered_file/public/spotify_0.jpg?itok=8-Ym-R61 (Spotify)
|
||||
[3]: https://www.linux.com/licenses/category/used-permission
|
||||
[5]: https://www.linux.com/sites/lcom/files/styles/rendered_file/public/clementine_0.jpg?itok=5oODJO3b (Clementine)
|
||||
[6]: http://www.radio-browser.info
|
||||
[8]: https://www.linux.com/sites/lcom/files/styles/rendered_file/public/odio.jpg?itok=sNPTSS3c (Odio)
|
||||
[10]: https://www.linux.com/sites/lcom/files/styles/rendered_file/public/streamtuner2.jpg?itok=1MSbafWj (Streamtuner2)
|
||||
[12]: https://www.linux.com/sites/lcom/files/styles/rendered_file/public/vlc_0.jpg?itok=QEOsq7Ii (VLC )
|
||||
[13]: https://training.linuxfoundation.org/linux-courses/system-administration-training/introduction-to-linux
|
||||
@ -0,0 +1,192 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (How To Remove/Delete The Empty Lines In A File In Linux)
|
||||
[#]: via: (https://www.2daygeek.com/remove-delete-empty-lines-in-a-file-in-linux/)
|
||||
[#]: author: (Magesh Maruthamuthu https://www.2daygeek.com/author/magesh/)
|
||||
|
||||
How To Remove/Delete The Empty Lines In A File In Linux
|
||||
======
|
||||
|
||||
Some times you may wants to remove or delete the empty lines in a file in Linux.
|
||||
|
||||
If so, you can use the one of the below method to achieve it.
|
||||
|
||||
It can be done in many ways but i have listed simple methods in the article.
|
||||
|
||||
You may aware of that grep, awk and sed commands are specialized for textual data manipulation.
|
||||
|
||||
Navigate to the following URL, if you would like to read more about these kind of topics. For **[creating a file in specific size in Linux][1]** multiple ways, for **[creating a file in Linux][2]** multiple ways and for **[removing a matching string from a file in Linux][3]**.
|
||||
|
||||
These are fall in advanced commands category because these are used in most of the shell script to do required things.
|
||||
|
||||
It can be done using the following 5 methods.
|
||||
|
||||
* **`sed Command:`** Stream editor for filtering and transforming text.
|
||||
* **`grep Command:`** Print lines that match patterns.
|
||||
* **`cat Command:`** It concatenate files and print on the standard output.
|
||||
* **`tr Command:`** Translate or delete characters.
|
||||
* **`awk Command:`** The awk utility shall execute programs written in the awk programming language, which is specialized for textual data manipulation.
|
||||
* **`perl Command:`** Perl is a programming language specially designed for text editing.
|
||||
|
||||
|
||||
|
||||
To test this, i had already created the file called `2daygeek.txt` with some texts and empty lines. The details are below.
|
||||
|
||||
```
|
||||
$ cat 2daygeek.txt
|
||||
2daygeek.com is a best Linux blog to learn Linux.
|
||||
|
||||
It's FIVE years old blog.
|
||||
|
||||
This website is maintained by Magesh M, it's licensed under CC BY-NC 4.0.
|
||||
|
||||
He got two GIRL babys.
|
||||
|
||||
Her names are Tanisha & Renusha.
|
||||
```
|
||||
|
||||
Now everything is ready and i’m going to test this in multiple ways.
|
||||
|
||||
### How To Remove/Delete The Empty Lines In A File In Linux Using sed Command?
|
||||
|
||||
Sed is a stream editor. A stream editor is used to perform basic text transformations on an input stream (a file or input from a pipeline).
|
||||
|
||||
```
|
||||
$ sed '/^$/d' 2daygeek.txt
|
||||
2daygeek.com is a best Linux blog to learn Linux.
|
||||
It's FIVE years old blog.
|
||||
This website is maintained by Magesh M, it's licensed under CC BY-NC 4.0.
|
||||
He got two GIRL babes.
|
||||
Her names are Tanisha & Renusha.
|
||||
```
|
||||
|
||||
Details are follow:
|
||||
|
||||
* **`sed:`** It’s a command
|
||||
* **`//:`** It holds the searching string.
|
||||
* **`^:`** Matches start of string.
|
||||
* **`$:`** Matches end of string.
|
||||
* **`d:`** Delete the matched string.
|
||||
* **`2daygeek.txt:`** Source file name.
|
||||
|
||||
|
||||
|
||||
### How To Remove/Delete The Empty Lines In A File In Linux Using grep Command?
|
||||
|
||||
grep searches for PATTERNS in each FILE. PATTERNS is one or patterns separated by newline characters, and grep prints each line that matches a pattern.
|
||||
|
||||
```
|
||||
$ grep . 2daygeek.txt
|
||||
or
|
||||
$ grep -Ev "^$" 2daygeek.txt
|
||||
or
|
||||
$ grep -v -e '^$' 2daygeek.txt
|
||||
2daygeek.com is a best Linux blog to learn Linux.
|
||||
It's FIVE years old blog.
|
||||
This website is maintained by Magesh M, it's licensed under CC BY-NC 4.0.
|
||||
He got two GIRL babes.
|
||||
Her names are Tanisha & Renusha.
|
||||
```
|
||||
|
||||
Details are follow:
|
||||
|
||||
* **`grep:`** It’s a command
|
||||
* **`.:`** Replaces any character.
|
||||
* **`^:`** matches start of string.
|
||||
* **`$:`** matches end of string.
|
||||
* **`E:`** For extended regular expressions pattern matching.
|
||||
* **`e:`** For regular expressions pattern matching.
|
||||
* **`v:`** To select non-matching lines from the file.
|
||||
* **`2daygeek.txt:`** Source file name.
|
||||
|
||||
|
||||
|
||||
### How To Remove/Delete The Empty Lines In A File In Linux Using awk Command?
|
||||
|
||||
The awk utility shall execute programs written in the awk programming language, which is specialized for textual data manipulation. An awk program is a sequence of patterns and corresponding actions.
|
||||
|
||||
```
|
||||
$ awk NF 2daygeek.txt
|
||||
or
|
||||
$ awk '!/^$/' 2daygeek.txt
|
||||
or
|
||||
$ awk '/./' 2daygeek.txt
|
||||
2daygeek.com is a best Linux blog to learn Linux.
|
||||
It's FIVE years old blog.
|
||||
This website is maintained by Magesh M, it's licensed under CC BY-NC 4.0.
|
||||
He got two GIRL babes.
|
||||
Her names are Tanisha & Renusha.
|
||||
```
|
||||
|
||||
Details are follow:
|
||||
|
||||
* **`awk:`** It’s a command
|
||||
* **`//:`** It holds the searching string.
|
||||
* **`^:`** matches start of string.
|
||||
* **`$:`** matches end of string.
|
||||
* **`.:`** Replaces any character.
|
||||
* **`!:`** Delete the matched string.
|
||||
* **`2daygeek.txt:`** Source file name.
|
||||
|
||||
|
||||
|
||||
### How To Delete The Empty Lines In A File In Linux using Combination of cat And tr Command?
|
||||
|
||||
cat stands for concatenate. It is very frequently used in Linux to reads data from a file.
|
||||
|
||||
cat is one of the most frequently used commands on Unix-like operating systems. It’s offer three functions which is related to text file such as display content of a file, combine multiple files into the single output and create a new file.
|
||||
|
||||
Translate, squeeze, and/or delete characters from standard input, writing to standard output.
|
||||
|
||||
```
|
||||
$ cat 2daygeek.txt | tr -s '\n'
|
||||
2daygeek.com is a best Linux blog to learn Linux.
|
||||
It's FIVE years old blog.
|
||||
This website is maintained by Magesh M, it's licensed under CC BY-NC 4.0.
|
||||
He got two GIRL babes.
|
||||
Her names are Tanisha & Renusha.
|
||||
```
|
||||
|
||||
Details are follow:
|
||||
|
||||
* **`cat:`** It’s a command
|
||||
* **`tr:`** It’s a command
|
||||
* **`|:`** Pipe symbol. It pass first command output as a input to another command.
|
||||
* **`s:`** Replace each sequence of a repeated character that is listed in the last specified SET.
|
||||
* **`\n:`** To add a new line.
|
||||
* **`2daygeek.txt:`** Source file name.
|
||||
|
||||
|
||||
|
||||
### How To Remove/Delete The Empty Lines In A File In Linux Using perl Command?
|
||||
|
||||
Perl stands in for “Practical Extraction and Reporting Language”. Perl is a programming language specially designed for text editing. It is now widely used for a variety of purposes including Linux system administration, network programming, web development, etc.
|
||||
|
||||
```
|
||||
$ perl -ne 'print if /\S/' 2daygeek.txt
|
||||
2daygeek.com is a best Linux blog to learn Linux.
|
||||
It's FIVE years old blog.
|
||||
This website is maintained by Magesh M, it's licensed under CC BY-NC 4.0.
|
||||
He got two GIRL babes.
|
||||
Her names are Tanisha & Renusha.
|
||||
```
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://www.2daygeek.com/remove-delete-empty-lines-in-a-file-in-linux/
|
||||
|
||||
作者：[Magesh Maruthamuthu][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://www.2daygeek.com/author/magesh/
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://www.2daygeek.com/create-a-file-in-specific-certain-size-linux/
|
||||
[2]: https://www.2daygeek.com/linux-command-to-create-a-file/
|
||||
[3]: https://www.2daygeek.com/empty-a-file-delete-contents-lines-from-a-file-remove-matching-string-from-a-file-remove-empty-blank-lines-from-a-file/
|
||||
107
sources/tech/20190211 How does rootless Podman work.md
Normal file
107
sources/tech/20190211 How does rootless Podman work.md
Normal file
@ -0,0 +1,107 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (How does rootless Podman work?)
|
||||
[#]: via: (https://opensource.com/article/19/2/how-does-rootless-podman-work)
|
||||
[#]: author: (Daniel J Walsh https://opensource.com/users/rhatdan)
|
||||
|
||||
How does rootless Podman work?
|
||||
======
|
||||
Learn how Podman takes advantage of user namespaces to run in rootless mode.
|
||||
|
||||
|
||||
In my [previous article][1] on user namespace and [Podman][2], I discussed how you can use Podman commands to launch different containers with different user namespaces giving you better separation between containers. Podman also takes advantage of user namespaces to be able to run in rootless mode. Basically, when a non-privileged user runs Podman, the tool sets up and joins a user namespace. After Podman becomes root inside of the user namespace, Podman is allowed to mount certain filesystems and set up the container. Note there is no privilege escalation here other then additional UIDs available to the user, explained below.
|
||||
|
||||
### How does Podman create the user namespace?
|
||||
|
||||
#### shadow-utils
|
||||
|
||||
Most current Linux distributions include a version of shadow-utils that uses the **/etc/subuid** and **/etc/subgid** files to determine what UIDs and GIDs are available for a user in a user namespace.
|
||||
|
||||
```
|
||||
$ cat /etc/subuid
|
||||
dwalsh:100000:65536
|
||||
test:165536:65536
|
||||
$ cat /etc/subgid
|
||||
dwalsh:100000:65536
|
||||
test:165536:65536
|
||||
```
|
||||
|
||||
The useradd program automatically allocates 65536 UIDs for each user added to the system. If you have existing users on a system, you would need to allocate the UIDs yourself. The format of these files is **username:STARTUID:TOTALUIDS**. Meaning in my case, dwalsh is allocated UIDs 100000 through 165535 along with my default UID, which happens to be 3265 defined in /etc/passwd. You need to be careful when allocating these UID ranges that they don't overlap with any **real** UID on the system. If you had a user listed as UID 100001, now I (dwalsh) would be able to become this UID and potentially read/write/execute files owned by the UID.
|
||||
|
||||
Shadow-utils also adds two setuid programs (or setfilecap). On Fedora I have:
|
||||
|
||||
```
|
||||
$ getcap /usr/bin/newuidmap
|
||||
/usr/bin/newuidmap = cap_setuid+ep
|
||||
$ getcap /usr/bin/newgidmap
|
||||
/usr/bin/newgidmap = cap_setgid+ep
|
||||
```
|
||||
|
||||
Podman executes these files to set up the user namespace. You can see the mappings by examining /proc/self/uid_map and /proc/self/gid_map from inside of the rootless container.
|
||||
|
||||
```
|
||||
$ podman run alpine cat /proc/self/uid_map /proc/self/gid_map
|
||||
0 3267 1
|
||||
1 100000 65536
|
||||
0 3267 1
|
||||
1 100000 65536
|
||||
```
|
||||
|
||||
As seen above, Podman defaults to mapping root in the container to your current UID (3267) and then maps ranges of allocated UIDs/GIDs in /etc/subuid and /etc/subgid starting at 1. Meaning in my example, UID=1 in the container is UID 100000, UID=2 is UID 100001, all the way up to 65536, which is 165535.
|
||||
|
||||
Any item from outside of the user namespace that is owned by a UID or GID that is not mapped into the user namespace appears to belong to the user configured in the **kernel.overflowuid** sysctl, which by default is 35534, which my /etc/passwd file says has the name **nobody**. Since your process can't run as an ID that isn't mapped, the owner and group permissions don't apply, so you can only access these files based on their "other" permissions. This includes all files owned by **real** root on the system running the container, since root is not mapped into the user namespace.
|
||||
|
||||
The [Buildah][3] command has a cool feature, [**buildah unshare**][4]. This puts you in the same user namespace that Podman runs in, but without entering the container's filesystem, so you can list the contents of your home directory.
|
||||
|
||||
```
|
||||
$ ls -ild /home/dwalsh
|
||||
8193 drwx--x--x. 290 dwalsh dwalsh 20480 Jan 29 07:58 /home/dwalsh
|
||||
$ buildah unshare ls -ld /home/dwalsh
|
||||
drwx--x--x. 290 root root 20480 Jan 29 07:58 /home/dwalsh
|
||||
```
|
||||
|
||||
Notice that when listing the home dir attributes outside the user namespace, the kernel reports the ownership as dwalsh, while inside the user namespace it reports the directory as owned by root. This is because the home directory is owned by 3267, and inside the user namespace we are treating that UID as root.
|
||||
|
||||
### What happens next in Podman after the user namespace is set up?
|
||||
|
||||
Podman uses [containers/storage][5] to pull the container image, and containers/storage is smart enough to map all files owned by root in the image to the root of the user namespace, and any other files owned by different UIDs to their user namespace UIDs. By default, this content gets written to ~/.local/share/containers/storage. Container storage works in rootless mode with either the vfs mode or with Overlay. Note: Overlay is supported only if the [fuse-overlayfs][6] executable is installed.
|
||||
|
||||
The kernel only allows user namespace root to mount certain types of filesystems; at this time it allows mounting of procfs, sysfs, tmpfs, fusefs, and bind mounts (as long as the source and destination are owned by the user running Podman. OverlayFS is not supported yet, although the kernel teams are working on allowing it).
|
||||
|
||||
Podman then mounts the container's storage if it is using fuse-overlayfs; if the storage driver is using vfs, then no mounting is required. Podman on vfs requires a lot of space though, since each container copies the entire underlying filesystem.
|
||||
|
||||
Podman then mounts /proc and /sys along with a few tmpfs and creates the devices in the container.
|
||||
|
||||
In order to use networking other than the host networking, Podman uses the [slirp4netns][7] program to set up **User mode networking for unprivileged network namespace**. Slirp4netns allows Podman to expose ports within the container to the host. Note that the kernel still will not allow a non-privileged process to bind to ports less than 1024. Podman-1.1 or later is required for binding to ports.
|
||||
|
||||
Rootless Podman can use user namespace for container separation, but you only have access to the UIDs defined in the /etc/subuid file.
|
||||
|
||||
### Conclusion
|
||||
|
||||
The Podman tool is enabling people to build and use containers without sacrificing the security of the system; you can give your developers the access they need without giving them root.
|
||||
|
||||
And when you put your containers into production, you can take advantage of the extra security provided by the user namespace to keep the workloads isolated from each other.
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/19/2/how-does-rootless-podman-work
|
||||
|
||||
作者：[Daniel J Walsh][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/rhatdan
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://opensource.com/article/18/12/podman-and-user-namespaces
|
||||
[2]: https://podman.io/
|
||||
[3]: https://buildah.io/
|
||||
[4]: https://github.com/containers/buildah/blob/master/docs/buildah-unshare.md
|
||||
[5]: https://github.com/containers/storage
|
||||
[6]: https://github.com/containers/fuse-overlayfs
|
||||
[7]: https://github.com/rootless-containers/slirp4netns
|
||||
@ -0,0 +1,68 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: ( )
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (What's the right amount of swap space for a modern Linux system?)
|
||||
[#]: via: (https://opensource.com/article/19/2/swap-space-poll)
|
||||
[#]: author: (David Both https://opensource.com/users/dboth)
|
||||
|
||||
What's the right amount of swap space for a modern Linux system?
|
||||
======
|
||||
Complete our survey and voice your opinion on how much swap space to allocate.
|
||||
|
||||
|
||||
Swap space is one of those things that everyone seems to have an idea about, and I am no exception. All my sysadmin friends have their opinions, and most distributions make recommendations too.
|
||||
|
||||
Many years ago, the rule of thumb for the amount of swap space that should be allocated was 2X the amount of RAM installed in the computer. Of course that was when a typical computer's RAM was measured in KB or MB. So if a computer had 64KB of RAM, a swap partition of 128KB would be an optimum size.
|
||||
|
||||
This took into account the fact that RAM memory sizes were typically quite small, and allocating more than 2X RAM for swap space did not improve performance. With more than twice RAM for swap, most systems spent more time thrashing than performing useful work.
|
||||
|
||||
RAM memory has become quite inexpensive and many computers now have RAM in the tens of gigabytes. Most of my newer computers have at least 4GB or 8GB of RAM, two have 32GB, and my main workstation has 64GB. When dealing with computers with huge amounts of RAM, the limiting performance factor for swap space is far lower than the 2X multiplier. As a consequence, recommended swap space is considered a function of system memory workload, not system memory.
|
||||
|
||||
Table 1 provides the Fedora Project's recommended size for a swap partition, depending on the amount of RAM in your system and whether you want enough memory for your system to hibernate. To allow for hibernation, you need to edit the swap space in the custom partitioning stage. The "recommended" swap partition size is established automatically during a default installation, but I usually find it's either too large or too small for my needs.
|
||||
|
||||
The [Fedora 28 Installation Guide][1] defines current thinking about swap space allocation. Note that other versions of Fedora and other Linux distributions may differ slightly, but this is the same table Red Hat Enterprise Linux uses for its recommendations. These recommendations have not changed since Fedora 19.
|
||||
|
||||
| Amount of RAM installed in system | Recommended swap space | Recommended swap space with hibernation |
|
||||
| --------------------------------- | ---------------------- | --------------------------------------- |
|
||||
| ≤ 2GB | 2X RAM | 3X RAM |
|
||||
| 2GB – 8GB | = RAM | 2X RAM |
|
||||
| 8GB – 64GB | 4G to 0.5X RAM | 1.5X RAM |
|
||||
| >64GB | Minimum 4GB | Hibernation not recommended |
|
||||
|
||||
Table 1: Recommended system swap space in Fedora 28's documentation.
|
||||
|
||||
Table 2 contains my recommendations based on my experiences in multiple environments over the years.
|
||||
| Amount of RAM installed in system | Recommended swap space |
|
||||
| --------------------------------- | ---------------------- |
|
||||
| ≤ 2GB | 2X RAM |
|
||||
| 2GB – 8GB | = RAM |
|
||||
| > 8GB | 8GB |
|
||||
|
||||
Table 2: My recommended system swap space.
|
||||
|
||||
It's possible that neither of these tables will work for your environment, but they will give you a place to start. The main consideration is that as the amount of RAM increases, adding more swap space simply leads to thrashing well before the swap space comes close to being filled. If you have too little virtual memory, you should add more RAM, if possible, rather than more swap space.
|
||||
|
||||
In order to test the Fedora (and RHEL) swap space recommendations, I used its recommendation of **0.5*RAM** on my two largest systems (the ones with 32GB and 64GB of RAM). Even when running four or five VMs, multiple documents in LibreOffice, Thunderbird, the Chrome web browser, several terminal emulator sessions, the Xfe file manager, and a number of other background applications, the only time I see any use of swap is during backups I have scheduled for every morning at about 2am. Even then, swap usage is no more than 16MB—yes megabytes. These results are for my system with my loads and do not necessarily apply to your real-world environment.
|
||||
|
||||
I recently had a conversation about swap space with some of the other Community Moderators here at [Opensource.com][2], and Chris Short, one of my friends in that illustrious and talented group, pointed me to an old [article][3] where he recommended using 1GB for swap space. This article was written in 2003, and he told me later that he now recommends zero swap space.
|
||||
|
||||
So, we wondered, what you think? What do you recommend or use on your systems for swap space?
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/19/2/swap-space-poll
|
||||
|
||||
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://docs.fedoraproject.org/en-US/fedora/f28/install-guide/
|
||||
[2]: http://Opensource.com
|
||||
[3]: https://chrisshort.net/moving-to-linux-partitioning/
|
||||
@ -1,103 +0,0 @@
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: (oska874)
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
[#]: subject: (Computer Laboratory – Raspberry Pi: Lesson 5 OK05)
|
||||
[#]: via: (https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/ok05.html)
|
||||
[#]: author: (Robert Mullins http://www.cl.cam.ac.uk/~rdm34)
|
||||
|
||||
translating by ezio
|
||||
|
||||
树莓派计算机实验室 课程 5 OK05
|
||||
======
|
||||
|
||||
OK05 课程构建于课程 OK04 的基础，使用更多代码方式烧、保存写莫尔斯码的 SOS 序列(`...---...`)。这里假设你已经有了 [课程 4: OK04][1] 操作系统的代码基础。
|
||||
|
||||
### 1 数据
|
||||
|
||||
到目前为止，我们与操作系统有关的所有内容都提供了遵循的说明。然而有时候，说明只是一半。我们的操作系统可能需要数据
|
||||
|
||||
> 一些早期的操作系统确实只允许特定文件中的特定类型的数据，但是这通常被认为太严格了。现代方法确实使程序变得复杂的多。
|
||||
|
||||
通常，只是数据的值很重要。你可能经过训练，认为数据是指定类型，比如，一个文本文件包含文章，一个图像文件包含一幅图片，等等。说实话，这只是一个理想罢了。计算机上的全部数据都是二进制数字，重要的是我们选择用什么来解释这些数据。在这个例子中，我们会将一个闪灯序列作为数据保存下来。
|
||||
|
||||
在 `main.s` 结束处复制下面的代码：
|
||||
|
||||
```
|
||||
.section .data %定义 .data 段
|
||||
.align 2 %对齐
|
||||
pattern: %定义整形变量
|
||||
.int 0b11111111101010100010001000101010
|
||||
```
|
||||
|
||||
>`.align num` 保证下一行代码的地址是 `2^num` 的整数倍。
|
||||
|
||||
>`.int val` 输出数值 `val`。
|
||||
|
||||
要区分数据和代码，我们将数据都放在 `.data` 区域。我已经将该区域包含在操作系统的内存布局图。我已经选择将数据放到代码后面。将我们的指令和数据分开保存的原因是，如果最后我们在自己的操作系统上实现一些安全措施，我们就需要知道代码的那些部分是可以执行的，而那些部分是不行的。
|
||||
|
||||
我在这里使用了两个新命令 `.align` 和 `.int`。`.align` 保证下来的数据是按照 2 的乘方对齐的。在这个里，我使用 `.align 2` ，意味着数据最终存放的地址是 `2^2=4` 的整数倍。这个操作是很重要的，因为我们用来读取内寸的指令 `ldr` 要求内存地址是 4 的倍数。
|
||||
|
||||
The .int command copies the constant after it into the output directly. That means that 111111111010101000100010001010102 will be placed into the output, and so the label pattern actually labels this piece of data as pattern.
|
||||
|
||||
命令 `.int` 直接复制它后面的常量到输出。这意味着 `11111111101010100010001000101010`(二进制数) 将会被存放到输出，所以标签模式实际将标记这段数据作为模式。
|
||||
|
||||
> 关于数据的一个挑战是寻找一个高效和有用的展示形式。这种保存一个开、关的时间单元的序列的方式，运行起来很容易，但是将很难编辑，因为摩尔斯的原理 `-` 或 `.` 丢失了。
|
||||
|
||||
如我提到的，数据可以意味这你想要的所有东西。在这里我编码了摩尔斯代码 SOS 序列，对于不熟悉的人，就是 `...---...`。我使用 0 表示一个时间单元的 LED 灭灯，而 1 表示一个时间单元的 LED 亮。这样，我们可以像这样编写一些代码在数据中显示一个序列，然后要显示不同序列，我们所有需要做的就是修改这段数据。下面是一个非常简单的例子，操作系统必须一直执行这段程序，解释和展示数据。
|
||||
|
||||
复制下面几行到 `main.s` 中的标记 `loop$` 之前。
|
||||
|
||||
```
|
||||
ptrn .req r4 %重命名 r4 为 ptrn
|
||||
ldr ptrn,=pattern %加载 pattern 的地址到 ptrn
|
||||
ldr ptrn,[ptrn] %加载地址 ptrn 所在内存的值
|
||||
seq .req r5 %重命名 r5 为 seq
|
||||
mov seq,#0 %seq 赋值为 0
|
||||
```
|
||||
|
||||
这段代码加载 `pattrern` 到寄存器 `r4`，并加载 0 到寄存器 `r5`。`r5` 将是我们的序列位置，所以我们可以追踪有多少 `pattern` 我们已经展示了。
|
||||
|
||||
下面的代码将非零值放入 `r1` ，如果仅仅是如果，这里有个 1 在当前位置的 `pattern`。
|
||||
|
||||
```
|
||||
mov r1,#1 %加载1到 r1
|
||||
lsl r1,seq %对r1 的值逻辑左移 seq 次
|
||||
and r1,ptrn %按位与
|
||||
```
|
||||
|
||||
这段代码对你调用 `SetGpio` 很有用，它必须有一个非零值来关掉 LED，而一个0值会打开 LED。
|
||||
|
||||
现在修改 `main.s` 中全部你的代码，这样代码中每次循环会根据当前的序列数设置 LED，等待 250000 毫秒（或者其他合适的延时），然后增加序列数。当这个序列数到达 32 就需要返回 0.看看你是否能实现这个功能，作为额外的挑战，也可以试着只使用一条指令。
|
||||
|
||||
### 2 Time Flies When You're Having Fun... 当你玩得开心时，过得很快
|
||||
|
||||
你现在准备好在树莓派上实验。应该闪烁一串包含 3 个短脉冲，3 个长脉冲，然后 3 个更短脉冲的序列。在一次延时之后，这种模式应该重复。如果这部工作，请查看我们的问题页。
|
||||
|
||||
一旦它工作，祝贺你已经达到 OK 系列教程的结束。
|
||||
|
||||
在这个谢列我们学习了汇编代码，GPIO 控制器和系统定时器。我们已经学习了函数和 ABI，以及几个基础的操作系统原理，和关于数据的知识。
|
||||
|
||||
你现在已经准备好下面几个更高级的课程的某一个。
|
||||
* [Screen][2] 系列是接下来的，会教你如何通过汇编代码使用屏幕。
|
||||
* [Input][3] 系列教授你如何使用键盘和鼠标。
|
||||
|
||||
到现在，你已经有了足够的信息来制作操作系统，用其它方法和 GPIO 交互。如果你有任何机器人工具，你可能会想尝试编写一个通过 GPIO 管教控制的机器人操作系统。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/ok05.html
|
||||
|
||||
作者：[Robert Mullins][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[ezio](https://github.com/oska874)
|
||||
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]: http://www.cl.cam.ac.uk/~rdm34
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/ok04.html
|
||||
[2]: https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/screen01.html
|
||||
[3]: https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/input01.html
|
||||
Loading…
Reference in New Issue
Block a user