Now that we know how to move around the file system, it’s time for a guided tour of our Linux system. Before we start however, we’re going to learn some more commands that will be useful along the way:

既然我们已经知道了如何在文件系统中跳转，是时候开始 Linux 操作系统之旅了。然而在开始之前，我们先学习一些对研究 Linux 系统有帮助的命令。

• ls – List directory contents
• file – Determine file type
• less – View file contents
• ls — 列出目录内容
• file — 确定文件类型
• less — 浏览文件内容

ls 的乐趣

The ls command is probably the most used command, and for good reason. With it, we can see directory contents and determine a variety of important file and directory attributes. As we have seen, we can simply type ls to see a list of files and subdirectories contained in the current working directory:

ls 可能是用户最常使用的命令了，这自有它的道理。通过 ls 命令，我们可以知道目录的内容，以及各种各样重要文件和目录的属性。正如我们已经见到的，只要简单地输入 ls 就能看到在当前目录下所有文件和子目录的列表。

[me@linuxbox ~]$ ls

Desktop Documents Music Pictures Publica Templates Videos
Besides the current working directory, we can specify the directory to list, like so:

除了当前工作目录以外，也可以指定别的目录，就像这样：

me@linuxbox ~]$ ls /usr
bin games   kerberos    libexec  sbin   src
etc include lib         local    share  tmp

Or even specify multiple directories. In this example we will list both the user’s home directory (symbolized by the “~” character) and the /usr directory:

甚至可以列出多个指定目录的内容。在这个例子中，将会列出用户家目录（用字符“~”代表）和/usr 目录的内容：

[me@linuxbox ~]$ ls ~ /usr
/home/me:
Desktop  Documents  Music  Pictures  Public  Templates  Videos

/usr:
bin  games      kerberos  libexec  sbin   src
etc  include    lib       local    share  tmp

We can also change the format of the output to reveal more detail:

我们也可以改变输出格式，来得到更多的细节：

[me@linuxbox ~]$ ls -l
total 56
drwxrwxr-x 2  me  me  4096  2007-10-26  17:20  Desktop
drwxrwxr-x 2  me  me  4096  2007-10-26  17:20  Documents
drwxrwxr-x 2  me  me  4096  2007-10-26  17:20  Music
drwxrwxr-x 2  me  me  4096  2007-10-26  17:20  Pictures
drwxrwxr-x 2  me  me  4096  2007-10-26  17:20  Public
drwxrwxr-x 2  me  me  4096  2007-10-26  17:20  Templates
drwxrwxr-x 2  me  me  4096  2007-10-26  17:20  Videos

By adding “-l” to the command, we changed the output to the long format.

使用 ls 命令的“-l”选项，则结果以长模式输出。

选项和参数

This brings us to a very important point about how most commands work. Commands are often followed by one or more options that modify their behavior, and further, by one or more arguments, the items upon which the command acts. So most commands look kind of like this:

我们将学习一个非常重要的知识点，即大多数命令是如何工作的。命令名经常会带有一个或多个用来更正命令行为的选项， 更进一步，选项后面会带有一个或多个参数，这些参数是命令作用的对象。所以大多数命令看起来像这样：

command -options arguments

注:
command : 命令
options : 选项
arguments : 参数

Most commands use options consisting of a single character preceded by a dash, for example, “-l”, but many commands, including those from the GNU Project, also support long options, consisting of a word preceded by two dashes. Also, many commands allow multiple short options to be strung together. In this example, the ls command is given two options, the “l” option to produce long format output, and the “t” option to sort the result by the file’s modification time.

大多数命令使用的选项，是由一个中划线加上一个字符组成，例如，“-l”，但是许多命令，包括来自于 GNU 项目的命令，也支持长选项，长选项由两个中划线加上一个字组成。当然， 许多命令也允许把多个短选项串在一起使用。下面这个例子，ls 命令有两个选项， “l” 选项产生长格式输出，“t”选项按文件修改时间的先后来排序。

[me@linuxbox ~]$ ls -lt

We’ll add the long option “–-reverse” to reverse the order of the sort:

加上长选项 “–-reverse”，则结果会以相反的顺序输出：

[me@linuxbox ~]$ ls -lt --reverse

The ls command has a large number of possible options. The most common are listed in the Table 4-1.

ls 命令有大量的选项。表4-1列出了最常使用的选项。

Table 4-1: Common ls Options

表 4-1: ls 命令选项

深入研究长格式输出

As we saw before, the “-l” option causes ls to display its results in long format. This format contains a great deal of useful information. Here is the Examples directory from an Ubuntu system:

正如我们先前知道的，“-l”选项导致 ls 的输出结果以长格式输出。这种格式包含大量的有用信息。下面的例子目录来自 于 Ubuntu 系统：

-rw-r--r-- 1 root root 3576296 2007-04-03 11:05 Experience ubuntu.ogg
-rw-r--r-- 1 root root 1186219 2007-04-03 11:05 kubuntu-leaflet.png
-rw-r--r-- 1 root root   47584 2007-04-03 11:05 logo-Edubuntu.png
-rw-r--r-- 1 root root   44355 2007-04-03 11:05 logo-Kubuntu.png
-rw-r--r-- 1 root root   34391 2007-04-03 11:05 logo-Ubuntu.png
-rw-r--r-- 1 root root   32059 2007-04-03 11:05 oo-cd-cover.odf
-rw-r--r-- 1 root root  159744 2007-04-03 11:05 oo-derivatives.doc
-rw-r--r-- 1 root root   27837 2007-04-03 11:05 oo-maxwell.odt
-rw-r--r-- 1 root root   98816 2007-04-03 11:05 oo-trig.xls
-rw-r--r-- 1 root root  453764 2007-04-03 11:05 oo-welcome.odt
-rw-r--r-- 1 root root  358374 2007-04-03 11:05 ubuntu Sax.ogg

Let’s look at the different fields from one of the files and examine their meanings:

选一个文件，来看一下各个输出字段的含义：

Table 4-2: ls Long Listing Fields

表 4-2: ls 长格式列表的字段

确定文件类型

As we explore the system it will be useful to know what files contain. To do this we will use the file command to determine a file’s type. As we discussed earlier, filenames in Linux are not required to reflect a file’s contents. While a filename like “picture.jpg” would normally be expected to contain a JPEG compressed image, it is not required to in Linux. We can invoke the file command this way:

随着探究操作系统的进行，知道文件包含的内容是很有用的。我们将用 file 命令来确定文件的类型。我们之前讨论过， 在 Linux 系统中，并不要求文件名来反映文件的内容。然而，一个类似 “picture.jpg” 的文件名，我们会期望它包含 JPEG 压缩图像，但 Linux 却不这样要求它。可以这样调用 file 命令：

file filename

When invoked, the file command will print a brief description of the file’s contents. For example:

当调用 file 命令后，file 命令会打印出文件内容的简单描述。例如：

[me@linuxbox ~]$ file picture.jpg
picture.jpg: JPEG image data, JFIF standard 1.01

There are many kinds of files. In fact, one of the common ideas in Unix-like operating systems such as Linux is that “everything is a file.” As we proceed with our lessons, we will see just how true that statement is.

有许多种类型的文件。事实上，在类 Unix 操作系统中比如说 Linux 中，有个普遍的观念就是“一切皆文件”。 随着课程的进行，我们将会明白这句话是多么的正确。

While many of the files on your system are familiar, for example MP3 and JPEG, there are many kinds that are a little less obvious and a few that are quite strange.

虽然系统中许多文件格式是熟悉的，例如 MP3和 JPEG 文件，但也有一些文件格式不太常见，极少数文件相当陌生。

用 less 浏览文件内容

The less command is a program to view text files. Throughout our Linux system, there are many files that contain human-readable text. The less program provides a convenient way to examine them.

less 命令是一个用来浏览文本文件的程序。纵观 Linux 系统，有许多人类可读的文本文件。less 程序为我们检查文本文件 提供了方便。

What Is “Text”

什么是“文本”

There are many ways to represent information on a computer. All methods involve defining a relationship between the information and some numbers that will be used to represent it. Computers, after all, only understand numbers and all data is converted to numeric representation.

在计算机中，有许多方法可以表达信息。所有的方法都涉及到，在信息与一些数字之间确立一种关系，而这些数字可以 用来代表信息。毕竟，计算机只能理解数字，这样所有的数据都被转换成数值来表示。

Some of these representation systems are very complex (such as compressed video files), while others are rather simple. One of the earliest and simplest is called ASCII text. ASCII (pronounced “As-Key”) is short for American Standard Code for Information Interchange. This is a simple encoding scheme that was first used on Teletype machines to map keyboard characters to numbers.

有些数值表达法非常复杂（例如压缩的视频文件），而其它的就相当简单。最早也是最简单的一种表达法，叫做 ASCII 文本。ASCII（发音是”As-Key”）是美国信息交换标准码的简称。这是一个简单的编码方法，它首先 被用在电传打字机上，用来实现键盘字符到数字的映射。

Text is a simple one-to-one mapping of characters to numbers. It is very compact. Fifty characters of text translates to fifty bytes of data. It is important to understand that text only contains a simple mapping of characters to numbers. It is not the same as a word processor document such as one created by Microsoft Word or OpenOffice.org Writer. Those files, in contrast to simple ASCII text, contain many non-text elements that are used to describe its structure and formatting. Plain ASCII text files contain only the characters themselves and a few rudimentary control codes like tabs, carriage returns and line feeds. Throughout a Linux system, many files are stored in text format and there are many Linux tools that work with text files. Even Windows recognizes the importance of this format. The well-known NOTEPAD.EXE program is an editor for plain ASCII text files.

文本是简单的字符与数字之间的一对一映射。它非常紧凑。五十个字符的文本翻译成五十个字节的数据。文本只是包含 简单的字符到数字的映射，理解这点很重要。它和一些文字处理器文档不一样，比如说由微软或 OpenOffice.org 文档 编辑器创建的文件。这些文件，和简单的 ASCII 文件形成鲜明对比，它们包含许多非文本元素，来描述它的结构和格式。 纯 ASCII 文件只包含字符本身，和一些基本的控制符，像制表符、回车符及换行符。纵观 Linux 系统，许多文件以文本格式存储，也有许多 Linux 工具来处理文本文件。甚至 Windows 也承认这种文件格式的重要性。著名的 NOTEPAD.EXE 程序就是一个纯 ASCII 文本文件编辑器。

Why would we want to examine text files? Because many of the files that contain system settings (called configuration files) are stored in this format, and being able to read them gives us insight about how the system works. In addition, many of the actual programs that the system uses (called scripts) are stored in this format. In later chapters, we will learn how to edit text files in order to modify systems settings and write our own scripts, but for now we will just look at their contents.

为什么我们要查看文本文件呢？ 因为许多包含系统设置的文件（叫做配置文件），是以文本格式存储的，阅读它们 可以更深入的了解系统是如何工作的。另外，许多系统所用到的实际程序（叫做脚本）也是以这种格式存储的。 在随后的章节里，我们将要学习怎样编辑文本文件以修改系统设置，还要学习编写自己的脚本文件，但现在我们只是看看它们的内容而已。

The less command is used like this:

less 命令是这样使用的：

less filename

Once started, the less program allows you to scroll forward and backward through a text file. For example, to examine the file that defines all the system’s user accounts, enter the following command:

一旦运行起来，less 程序允许你前后滚动文件。例如，要查看一个定义了系统中全部用户身份的文件，输入以下命令：

[me@linuxbox ~]$ less /etc/passwd

Once the less program starts, we may view the contents of the file. If the file is longer than one page, we can scroll up and down. To exit less, press the “q” key. The table below lists the most common keyboard commands used by less.

一旦 less 程序运行起来，我们就能浏览文件内容了。如果文件内容多于一页，那么我们可以上下滚动文件。按下“q”键， 退出 less 程序。

下表列出了 less 程序最常使用的键盘命令。

Table 4-3: less Commands

表 4-3: less 命令

less 就是 more（禅语：色即是空）

The less program was designed as an improved replacement of an earlier Unix program called more. The name “less” is a play on the phrase “less is more”—a motto of modernist architects and designers.

less 程序是早期 Unix 程序 more 的改进版。“less” 这个名字，对习语 “less is more” 开了个玩笑， 这个习语是现代主义建筑师和设计者的座右铭。

less falls into the class of programs called “pagers,” programs that allow the easy viewing of long text documents in a page by page manner. Whereas the more program could only page forward, the less program allows paging both forward and backward and has many other features as well.

less 属于”页面调度器”类程序，这些程序允许以逐页方式轻松浏览长文本文档。 more 程序只能向前翻页，而 less 程序允许前后翻页，此外还有很多其它的特性。

旅行指南

The file system layout on your Linux system is much like that found on other Unix-like systems. The design is actually specified in a published standard called the Linux Filesystem Hierarchy Standard. Not all Linux distributions conform to the standard exactly but most come pretty close.

Linux 系统中，文件系统布局与类 Unix 系统的文件布局很相似。实际上，一个已经发布的标准， 叫做 Linux 文件系统层次标准，详细说明了这种设计模式。不是所有Linux发行版都根据这个标准，但 大多数都是。

Next, we are going to wander around the file system ourselves to see what makes our Linux system tick. This will give you a chance to practice your navigation skills. One of the things we will discover is that many of the interesting files are in plain human- readable text. As we go about our tour, try the following:

下一步，我们将在文件系统中游览，来了解 Linux 系统的工作原理。这会给你一个温习跳转命令的机会。 我们会发现很多有趣的文件都是纯人类可读文本。下面旅行开始，做做以下练习：

1. cd into a given directory

2. List the directory contents with ls -l

3. If you see an interesting file, determine its contents with file

4. If it looks like it might be text, try viewing it with less

5. cd 到给定目录

6. 列出目录内容 ls -l

7. 如果看到一个有趣的文件，用 file 命令确定文件内容

8. 如果文件看起来像文本，试着用 less 命令浏览它

Remember the copy and paste trick! If you are using a mouse, you can double click on a filename to copy it and middle click to paste it into commands.

记得复制和粘贴技巧！如果你正在使用鼠标，双击文件名，来复制它，然后按下鼠标中键，粘贴文件名到命令行中。

As we wander around, don’t be afraid to look at stuff. Regular users are largely prohibited from messing things up. That’s the system administrators job! If a command complains about something, just move on to something else. Spend some time looking around. The system is ours to explore. Remember, in Linux, there are no secrets! Table 4-4 lists just a few of the directories we can explore. Feel free to try more!

在系统中游览时，不要害怕四处看看。普通用户是很难把东西弄乱的。那是系统管理员的工作！ 如果一个命令抱怨一些事情，不要管它，尝试一下别的东西。花一些时间四处看看。 系统是我们自己的，尽情地探究吧。记住在 Linux 中，没有秘密存在！ 表4-4仅仅列出了一些我们可以浏览的目录。随意尝试更多！

Table 4-4: Directories Found On Linux Systems

表 4-4: Linux 系统中的目录 ★★★

符号链接

As we look around, we are likely to see a directory listing with an entry like this:

在我们到处查看时，我们可能会看到一个目录，列出像这样的一条信息：

lrwxrwxrwx 1 root root 11 2007-08-11 07:34 libc.so.6 -> libc-2.6.so

Notice how the first letter of the listing is “l” and the entry seems to have two filenames? This is a special kind of a file called a symbolic link (also known as a soft link or symlink.) In most Unix-like systems it is possible to have a file referenced by multiple names. While the value of this may not be obvious, it is really a useful feature.

注意看，为何这条信息第一个字符是“l”，并且有两个文件名呢？ 这是一个特殊文件，叫做符号链接（也称为软链接或者 symlink ）。 在大多数“类 Unix” 系统中， 有可能一个文件被多个文件名所指向。虽然这种特性的意义并不明显，但它真的很有用。

Picture this scenario: a program requires the use of a shared resource of some kind contained in a file named “foo,” but “foo” has frequent version changes. It would be good to include the version number in the filename so the administrator or other interested party could see what version of “foo” is installed. This presents a problem. If we change the name of the shared resource, we have to track down every program that might use it and change it to look for a new resource name every time a new version of the resource is installed. That doesn’t sound like fun at all.

描绘一下这样的情景：一个程序要求使用某个包含在名为“foo”文件中的共享资源，但是“foo”经常改变版本号。 这样，在文件名中包含版本号，会是一个好主意，因此管理员或者其它相关方，会知道安装了哪个“foo”版本。 这会导致另一个问题。如果我们更改了共享资源的名字，那么我们必须跟踪每个可能使用了 这个共享资源的程序，当每次这个资源的新版本被安装后，都要让使用了它的程序去寻找新的资源名。 这听起来很没趣。

Here is where symbolic links save the day. Let’s say we install version 2.6 of “foo,” which has the filename “foo-2.6” and then create a symbolic link simply called “foo” that points to “foo-2.6.” This means that when a program opens the file “foo”, it is actually opening the file “foo-2.6”. Now everybody is happy. The programs that rely on “foo” can find it and we can still see what actual version is installed. When it is time to upgrade to “foo-2.7,” we just add the file to our system, delete the symbolic link “foo” and create a new one that points to the new version. Not only does this solve the problem of the version upgrade, but it also allows us to keep both versions on our machine. Imagine that “foo-2.7” has a bug (damn those developers!) and we need to revert to the old version. Again, we just delete the symbolic link pointing to the new version and create a new symbolic link pointing to the old version.

符号链接避免了这种情况。比方说，我们安装了文件 “foo” 的 2.6 版本，它的文件名是 “foo-2.6”，然后创建了叫做 “foo” 的符号链接，这个符号链接指向 “foo-2.6”。 这意味着，当一个程序打开文件 “foo” 时，它实际上是打开文件 “foo-2.6”。 现在，每个人都很高兴。依赖于 “foo” 文件的程序能找到这个文件，并且我们能知道安装了哪个文件版本。 当升级到 “foo-2.7” 版本的时候，仅添加这个文件到文件系统中，删除符号链接 “foo”， 创建一个指向新版本的符号链接。这不仅解决了版本升级问题，而且还允许在系统中保存两个不同的文件版本。 假想 “foo-2.7” 有个错误（该死的开发者！），那我们得回到原来的版本。 一样的操作，我们只需要删除指向新版本的符号链接，然后创建指向旧版本的符号链接就可以了。

The directory listing above (from the /lib directory of a Fedora system) shows a symbolic link called “libc.so.6” that points to a shared library file called “libc-2.6.so.” This means that programs looking for “libc.so.6” will actually get the file “libc-2.6.so.” We will learn how to create symbolic links in the next chapter.

在上面列出的目录（来自于 Fedora 的 /lib 目录）展示了一个叫做 “libc.so.6” 的符号链接，这个符号链接指向一个 叫做 “libc-2.6.so” 的共享库文件。这意味着，寻找文件 “libc.so.6” 的程序，实际上得到是文件 “libc-2.6.so”。 在下一章节，我们将学习如何建立符号链接。

硬链接

While we are on the subject of links, we need to mention that there is a second type of link called a hard link. Hard links also allow files to have multiple names, but they do it in a different way. We’ll talk more about the differences between symbolic and hard links in the next chapter.

讨论到链接问题，我们需要提一下，还有一种链接类型，叫做硬链接。硬链接同样允许文件有多个名字， 但是硬链接以不同的方法来创建多个文件名。在下一章中，我们会谈到更多符号链接与硬链接之间的差异问题。

拓展阅读

• The full version of the Linux Filesystem Hierarchy Standard can be found here:
• 完整的 Linux 文件系统层次体系标准可通过以下链接找到：
  http://www.pathname.com/fhs/