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Translating by qhwdw Migrating to Linux: Disks, Files, and Filesystems
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============================================================
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Installing and using Linux on your main desktop will help you quickly become familiar with the methods and tools you need.[Creative Commons Zero][1]Pixabay
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This is the second article in our series on migrating to Linux. If you missed the first one, [you can find it here][4]. As mentioned previously, there are several reasons why you might want to migrate to Linux. You might be using or developing code for Linux in your job, or you might just want to try something new.
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In any case, having Linux on your main desktop will help you quickly become familiar with the methods and tools you’ll need. In this article, I’ll provide an introduction to Linux files, filesystems and disks.
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### Where's My C:\?
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If you are coming from a Mac, Linux should feel fairly familiar to you, as the Mac uses files, filesystems, and disks pretty closely to the way Linux does. On the other hand, if your experience is primarily Windows, accessing disks under Linux may seem a little confusing. Generally, Windows assigns a drive letter (like C:\) to each disk. Linux does not do this. Instead Linux presents a single hierarchy of files and directories for everything in your system.
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Let's look at an example. Suppose you use a computer with a main hard drive, a CD-ROM with folders called _Books_ and _Videos_ and a USB thumb drive with a directory called _Transfer_ . Under Windows, you would see the following:
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```
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C:\ [Hard drive]
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├ System
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├ System32
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├ Program Files
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├ Program Files (x86)
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└ <additional folders>
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D:\ [CD-ROM]
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├ Books
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└ Videos
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E:\ [USB thumb drive]
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└ Transfer
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```
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A typical Linux system would instead have this:
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```
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/ (the top most directory, called the root directory) [Hard drive]
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├ bin
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├ etc
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├ lib
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├ sbin
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├ usr
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├ <additional directories>
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└ media
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└ <your user name>
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├ cdrom [CD-ROM]
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│ ├ Books
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│ └ Videos
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└ Kingme_USB [USB thumb drive]
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└ Transfer
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```
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If you are using a graphical environment, usually, the file manager in Linux will present the CD-ROM and the USB thumb drive with icons that look like the device, so you may not need to know the media's specific directory.
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### Filesystems
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Linux emphasizes these things called filesystems. A filesystem is a set of structures on media (like a hard drive) that keep track of all the files and directories on the media. Without a filesystem we could store information on a hard drive, but all the data would be in a jumbled mess. We wouldn't know which blocks of data belonged to which file. You may have heard of names like Ext4, XFS, and Btrfs. These are Linux filesystem types.
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Every type of media that holds files and directories has a filesystem on it. Different media types may use specific filesystem types that are optimized for the media. So CD-ROMs use ISO9660 or UDF filesystem types. USB thumbdrives typically use FAT32 so they can be easily shared with other computer systems.
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Windows uses filesystems, too. It just doesn't talk about them as much. For example, when you insert a CD-ROM, Windows will read the ISO9660 filesystem structures, assign a drive letter to it and display the files and directories under the letter (D:\ for example). So if you're picky about details, technically Windows assigns a drive letter to a filesystem, not the whole disk.
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Using that same example, Linux will also read the ISO9660 filesystem structures, but instead of a drive letter, it will attach the filesystem to a directory (a process called mounting). Linux will then display the files and directories on the CD-ROM under the attached directory ( _/media/<your user name>/cdrom,_ for example).
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So to answer the question "Where's my C:\?" On Linux, there is no C:\. It works differently.
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### Files
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Windows stores files and directories (also called folders) in its filesystem. Linux, however, lets you put other things into the filesystem as well. These additional types of things are native objects in the filesystem, and they're actually different from regular files. Linux allows you to create and use hard links, symbolic links, named pipes, device nodes, and sockets, in addition to the regular files and directories. We won't get into all the types of filesystem objects here, but there are a few that are useful to know about.
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Hard links are used to create one or more aliases for a file. Each alias is a different name to the same contents on disk. If you edit the file under one file name, the changes appear under the other file names as well. For example. you might have _MyResume_2017.doc_ also have a hard link called _JaneDoeResume.doc_ . (Note that you can create a hard link by using the _ln_ command from the command line.) This way you can find and edit _MyResume_2017.doc_ , then send out _JaneDoeResume.doc_ to your prospects to help them keep track where it's from -- which will contain all your updates.
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Symbolic links are a little like Windows shortcuts. The filesystem entry contains a path to another file or directory. In a lot of ways, they work like hard links in that they can create an alias to another file. However, symbolic links can alias directories as well as files, and symbolic links can refer to items in a different filesystem on different media where hard links cannot. (Note that you can create symbolic links also with the _ln_ command, but with the _-s_ option.)
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### Permissions
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Another big difference between Windows and Linux involves the permissions on filesystem objects (files, directories, and others). Windows implements a fairly complex set of permissions on files and directories. For example, users and groups can have permissions to read, write, execute, modify, and more. Users and groups can be given permission to access everything in a directory with exceptions, or they can be given no permission to anything in a directory with exceptions.
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Most folks using Windows don't make use of special permissions, however; so, it's surprising when they discover that a default set of permissions are used and enforced on Linux. Linux can enforce more sophisticated permissions by using SELinux or AppArmor. However most Linux installations just use the built-in default permissions.
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In the default permissions, each item in the filesystem has a set of permissions for the owner of the file, the group for the file, and for everyone else. These permissions allow for: reading, writing, and executing. The permissions have a hierarchy to them. First, it checks whether the user (the login name) is the owner and has permission. If not, then it checks whether your user (login name) is in the group for the file and the group has permission. If not, then it checks whether everyone else has permission. There are other permission settings as well, but the three sets of three are the ones most commonly used.
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If you are using the command line, and you type ls -l, you may see permissions represented as:
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```
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rwxrw-r-- 1 stan dndgrp 25 Oct 33rd 25:01 rolldice.sh
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```
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The letters at the beginning, rwxrw-r--, show the permissions. In this case, the owner (stan) can read, write, and execute the file (the first three letters, rwx); members of the group dndgrp can read and write the file but not execute (the second three letters, rw-); and everyone else can only read the file (the last three letters, r--).
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(Note that on Windows to make a script executable, you make the file's extension something specific, .bat for example. On Linux, the file's extension doesn't mean anything to the operating system. Instead its permissions need to be set so the file is executable.)
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If you get a _permission denied_ error, chances are you are attempting to run a program or command that requires administrator privilege, or you're trying to access a file that doesn't hold permissions for your user account to access it. If you are trying to do something that requires administrator privilege, you will need to switch to the user account called _root_ by logging in as root, or by using a helper program called _sudo_ on the command line, which will allow you to temporarily run as root. The sudo tool will, of course, ask for a password to make sure you really should have permission.
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### Hard Drive Filesystems
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Windows predominately uses a filesystem type called NTFS for hard drives. On Linux, you get to pick which type of filesystem you want to use for the hard drive. Different types of filesystems exhibit different features and different performance characteristics. The main native Linux filesystem used today is Ext4\. However, you can choose from an abundance of filesystem types at installation time, such as: Ext3 (predecessor to Ext4), XFS, Btrfs, UBIFS (for embedded systems), and more. If you're not sure which one to use, Ext4 will work great.
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_Learn more about Linux through the free ["Introduction to Linux" ][2]course from The Linux Foundation and edX._
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--------------------------------------------------------------------------------
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via: https://www.linux.com/blog/learn/intro-to-linux/2017/11/migrating-linux-disks-files-and-filesystems
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作者：[JOHN BONESIO][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://www.linux.com/users/johnbonesio
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[1]:https://www.linux.com/licenses/category/creative-commons-zero
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[2]:https://training.linuxfoundation.org/linux-courses/system-administration-training/introduction-to-linux
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[3]:https://www.linux.com/files/images/butterflies-8075511920jpg
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[4]:https://www.linux.com/blog/learn/intro-to-linux/2017/10/migrating-linux-introduction
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@ -0,0 +1,135 @@
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迁移到 Linux：磁盘、文件、和文件系统
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============================================================
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在你的主要桌面上安装和使用 Linux 将帮你快速熟悉你需要的工具和方法。[Creative Commons Zero][1]Pixabay
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这是我们的迁移到 Linux 系列文章的第二篇。如果你错过了第一篇，[你可以在这里找到它][4]。以前提到过，为什么要迁移到 Linux 的几个原因。你可以在你的工作中为 Linux 开发和使用代码，或者，你可能是正想去尝试一下新事物。
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不论是什么原因，拥有一个 Linux 的主桌面，将帮助你快速熟悉你需要的工具和方法。在这篇文章中，我将介绍 Linux 的文件、文件系统和磁盘。
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### 我的 C:\ 在哪里？
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如果你是一个 Mac 用户，Linux 对你来说应该非常熟悉，Mac 使用的文件、文件系统、和磁盘与 Linux 是非常接近的。另一方面，如果你的使用经验主要是 Windows，访问 Linux 下的磁盘可能看上去有点困惑。一般，Windows 给每个磁盘分配一个盘符（像 C:\）。而 Linux 并不是这样。而在你的 Linux 系统中它是一个单一的文件和目录的层次结构。
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让我们看一个示例。假设你的计算机使用了一个主硬盘、一个有 _Books_ 和 _Videos_ 目录的 CD-ROM 、和一个有 _Transfer_ 目录的 U 盘，在你的 WIndows 下，你应该看到的是下面的样子：
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```
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C:\ [Hard drive]
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├ System
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├ System32
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├ Program Files
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├ Program Files (x86)
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└ <additional folders>
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D:\ [CD-ROM]
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├ Books
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└ Videos
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E:\ [USB thumb drive]
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└ Transfer
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```
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而一个典型的 Linux 系统却是这样：
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```
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/ (the top most directory, called the root directory) [Hard drive]
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├ bin
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├ etc
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├ lib
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├ sbin
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├ usr
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├ <additional directories>
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└ media
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└ <your user name>
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├ cdrom [CD-ROM]
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│ ├ Books
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│ └ Videos
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└ Kingme_USB [USB thumb drive]
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└ Transfer
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```
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如果你使用一个图形化环境，通常，Linux 中的文件管理器将出现看起来像驱动器的图标的 CD-ROM 和 USB 便携式驱动器，因此，你根本就无需知道介质所在的目录。
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### 文件系统
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Linux 称这些东西为文件系统。一个文件系统是在介质（比如，硬盘）上保持跟踪所有的文件和目录的一组结构。如果没有文件系统，我们存储在硬盘上的信息就会混乱，我们就不知道哪个块属于哪个文件。你可能听到过一些名字，比如，Ext4、XFS、和 Btrfs。这些都是 Linux 文件系统。
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每个保存有文件和目录的介质都有一个文件系统在上面。不同的介质类型可能使用了为它优化过的特定的文件系统。比如，CD-ROMs 使用 ISO9660 或者 UDF 文件系统类型。USB 便携式驱动器一般使用 FAT32，以便于它们可以很容易去与其它计算机系统共享。
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Windows 也使用文件系统。不过，我们不过多的讨论它。例如，当你插入一个 CD-ROM，Windows 将读取 ISO9660 文件系统结构，分配一个盘符给它，然后，在盘符（比如，D:\）下显示文件和目录。当然，如果你深究细节，从技术角度说，Windows 是分配一个盘符给一个文件系统，而不是整个驱动器。
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使用同样的例子，Linux 也读取 ISO9660 文件系统结构，但它不分配盘符，它附加文件系统到一个目录（这个过程被称为加载）。Linux 将随后在附加的目录（比如是， _/media/<your user name>/cdrom_ ）下显示 CD-ROM 上的文件和目录。
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因此，在 Linux 上回答 “我的 C:\ 在哪里？” 这个问题，答案是，这里没有 C:\，它们工作方式不一样。
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### 文件
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Windows 在它的文件系统中存在文件和目录（也被称为文件夹）。但是，Linux 也让你将其它的东西放到文件系统中。这些其它类型的东西是文件系统的原生的对象，并且，它们和普通文件实际上是不同的。除普通文件和目录之外，Linux 还允许你去创建和使用硬链接、符号链接、命名管道、设备节点、和套接字。在这里，我们不展开讨论所有的文件系统对象的类型，但是，这里有几种经常使用到的。
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硬链接是用于为文件创建一个或者多个别名。指向磁盘上同样内容的每个别名的名字是不同的。如果在一个文件名下编辑文件，这个改变也同时出现在其它的文件名上。例如，你有一个 _MyResume_2017.doc_，它还一个被称为 _JaneDoeResume.doc_ 的硬链接。（注意，硬链接是从命令行下，使用 _ln_ 的命令去创建的）。你可以找到并编辑 _MyResume_2017.doc_，然后，然后找到 _JaneDoeResume.doc_，你发现它保持了跟踪 -- 它包含了你所有的更新。
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符号链接有点像 Windows 中的快捷方式。文件系统的入口包含一个到其它文件或者目录的路径。在很多方面，它们的工作方式和硬链接很相似，它们可以创建一个到其它文件的别名。但是，符号链接也可以像文件一样给目录创建一个别名，并且，符号链接可以指向到不同介质上的不同文件系统，而硬链接做不到这些。（注意，你可以使用带 _-s_ 选项的 _ln_ 命令去创建一个符号链接）
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### 权限
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另一个很大的区别是文件系统对象上在 Windows 和 Linux 之中涉及的权限（文件、目录、及其它）。Windows 在文件和目录上实现了一套非常复杂的权限。例如，用户和用户组可以有权限去读取、写入、运行、修改、等等。用户和用户组可以授权访问除例外以外的目录中的所有内容，也可以不允许访问除例外的目录中的所有内容。
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然而，大多数使用 Windows 的人并不去使用一个特定的权限；因此，当他们发现使用一套权限并且在 Linux 上是强制执行的，他们感到非常惊讶！Linux 通过使用 SELinux 或者 AppArmor 可以强制执行一套更复杂的权限。但是，大多数 Linux 安装版都使用了内置的默认权限。
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在默认的权限中，文件系统中的每个条目都有一套为它的文件所有者、文件所在的组、和其它人的权限。这些权限允许他们：读取、写入、和运行。给它们的权限有一个层次。首先，它检查这个（登入的）用户是否为该文件所有者和它拥有的权限。如果不是，然后检查这个用户是否在文件所在的组中和它拥有的权限。如果不是，然后它再检查其它人拥有的权限。这里设置了其它人的权限。但是，这里设置的三套权限大多数情况下都会使用其中的一套。
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如果你使用命令行，你输入 `ls -l`，你可以看到如下所表示的权限：
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```
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rwxrw-r-- 1 stan dndgrp 25 Oct 33rd 25:01 rolldice.sh
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```
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最前面的字母，`rwxrw-r--`，展示了权限。在这个例子中，所有者（stan）可以读取、写入、和运行这个文件（前面的三个字母，rwx）；dndgrp 组的成员可以读取和写入这个文件，但是不能运行（第二组的三个字母，rw-）；其它人仅可以读取这个文件（最后的三个字母，r--）。
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（注意，在 Windows 中去生成一个可运行的脚本，你生成的文件有一个特定的扩展名，比如 .bat，而在 Linux 中，扩展名在操作系统中没有任何意义。而是需要去设置这个文件可运行的权限）
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如果你收到一个 _permission denied_ 错误，可能是你去尝试运行了一个要求管理员权限的程序或者命令，或者你去尝试访问一个你的帐户没有访问权限的文件。如果你尝试去做一些要求管理员权限的事，你必须切换登入到一个被称为 _root_ 的用户帐户。或者通过使用一个命令行的被称为 _sudo_ 的助理程序。它可以临时允许你以 _root_ 权限运行。当然，_sudo_ 工具，也会要求你输入密码，以确保你真的有权限。
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### 硬盘文件系统
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Windows 主要使用一个被称为 `NTFS` 的硬盘文件系统。在 Linux 上，你也可以选一个你希望去使用的硬盘文件系统。不同的文件系统类型呈现不同的特性和不同的性能特征。主要的原生 Linux 的文件系统，现在使用的是 Ext4。但是，在安装 Linux 的时候，你可以有丰富的文件系统类型可供选择，比如，Ext3（Ext4 的前任）、XFS、Btrfs、UBIFS（用于嵌入式系统）、等等。如果你不确定要使用哪一个，Ext4 是一个很好的选择。
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_通过来自 Linux 基金会和 edX 的 ["Linux 介绍"][2] 上免费学习更多的 Linux 课程。_
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--------------------------------------------------------------------------------
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via: https://www.linux.com/blog/learn/intro-to-linux/2017/11/migrating-linux-disks-files-and-filesystems
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作者：[JOHN BONESIO][a]
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译者：[qhwdw](https://github.com/qhwdw)
|
||||
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/johnbonesio
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[1]:https://www.linux.com/licenses/category/creative-commons-zero
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||||
[2]:https://training.linuxfoundation.org/linux-courses/system-administration-training/introduction-to-linux
|
||||
[3]:https://www.linux.com/files/images/butterflies-8075511920jpg
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||||
[4]:https://www.linux.com/blog/learn/intro-to-linux/2017/10/migrating-linux-introduction
|
||||
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