Keep it simple, stupid

Friday, 29. December 2006, 15:46:07

有时候我们开机的时候也许没有必要进入X-window界面。比如，我开机只是为了编译一个东西，或者是写一段程序，我可以在console下可以更高效的完成，例如编译软件的时候使用console会大大的提高编译效率。(甚至我用vi写程序的时候仍然可以使用mplayer播放歌曲。)

安装完一个发行版后，一般默认启动的是x-window，我们可以通过更改
/etc/inittab
中的
id:5:initdefault:
这一行来实现开机默认启动X还是console。(3为console,5为X-window)

当然这有点不太现实，因为我们无法在开机的时候决定这个文件的内容，所以最好的办法是如果能在grub中选择。

下面是实现的办法：
更改/etc/grub.conf文件

title Fedora Core (X-window)
        root (hd0,2)
        kernel /boot/vmlinuz-2.6.18-1.2239.fc5 ro root=LABEL=/12 rhgb quiet vga=0x305
        initrd /boot/initrd-2.6.18-1.2239.fc5.img
title Fedora Core (text console)
        root (hd0,2)
        kernel /boot/vmlinuz-2.6.18-1.2239.fc5 ro root=LABEL=/12 rhgb quiet vga=0x305 3
        initrd /boot/initrd-2.6.18-1.2239.fc5.img

其实很简单的，新增加一个启动的项目，在kernel最后一行加一数字3，进入level3模式(多用户console模式)

vga=0x305代表启动vga图形驱动模式，设置分辨率为0x305(1024x768)

觉得1024x768下的console更cool!

关于linux启动可以参考：Linux’s boot process explained

Friday, 29. December 2006, 05:04:33

改了一下locale，结果不能输入中文了，仔细看了一下关于locale，收获挺大的。

locale 是国际化与本土化过程中的一个非常重要的概念，个人认为，对于中文用户来说，通常会涉及到的国际化或者本土化，大致包含三个方面：看中文，写中文，与 window中文系统的兼容和通信。从实际经验上看来，locale的设定与看中文关系不大，但是与写中文，及window分区的挂载方式有很密切的关系。本人认为就像一个纯英文的Windows能够浏览中文，日文或者意大利文网页一样，你不需要设定locale就可以看中文。那么，为什么要设定 locale呢？什么时候会用到locale呢？

一、为什么要设定locale 正如前面我所讲的，设定locale与你能否浏览中文的网页没有直接的关系，即便你把locale设置成en_US.ISO-8859-1这样一个标准的英文locale你照样可以浏览中文的网页，只要你的系统里面有相应的字符集（这个都不一定需要）和合适的字体（如simsun），浏览器就可以把网页翻译成中文给你看。具体的过程是网络把网页传送到你的机器上之后，浏览器会判断相应的编码的字符集，根据网页采用的字符集，去字体库里面找合适的字体，然后由文字渲染工具把相应的文字在屏幕上显示出来。

在下文本人会偶尔把字符集比喻成密码本，个人觉得对于一些东西比较容易理解，假如你不习惯的话，把全文copy到任何文本编辑器，用字符集替换密码本即可。

那有时候网页显示乱码或者都是方框是怎么回事呢？个人认为，显示乱码是因为设定的字符集不对(或者没有相应的字符集)，例如网页是用UTF-8编码的，你非要用GB2312去看，而系统根据GB2312去找字体，然后在屏幕上显示，当然是一堆的乱码，也就是说你用一个错误的密码本去翻译发给你的电报，当然内容那叫一个乱；至于有些时候浏览的网页能显示一部分汉字，但有很多的地方是方框，能够显示汉字说明浏览器已经正确的判断出了网页的编码，并在字体库里面找到了相应的文字，但是并不是每个字体库都包含某个字符集全部的字体的缘故，有些时候会显示不完全，找一个比较全的支持较多字符集的字体就可以了。

既然我能够浏览中文网页，那为什么我还要设定locale呢？

其实你有没有想过这么一个问题，为什么gentoo官方论坛上中文论坛的网页是用UTF-8编码的（虽然大家一直强烈建议用GB2312编码），但是新浪网就是用GB2312编码的呢？而Xorg的官方网页竟然是ISO-8859-15编码的，我没有设定这个locale怎么一样的能浏览呢？这个问题就像是你有所有的密码本，不论某个网站是用什么字符集编码的，你都可以用你手里的密码本把他们翻译过来，但问题是虽然你能浏览中文网页，但是在整个操作系统里面流动的还是英文字符。所以，就像你能听懂英语，也能听懂中文。 最根本的问题是：你不可以写中文。

当你决定要写什么东西的时候，首先要决定的一件事情是用那种语言，对于计算机来说就是你要是用哪一种字符集，你就必须告诉你的linux系统，你想用那一本密码本去写你想要写的东西。知道为什么需要用GB2312字符集去浏览新浪了吧，因为新浪的网页是用GB2312写的。

为了让你的Linux能够输入中文，就需要把系统的locale设定成中文的(严格说来是locale中的语言类别LC_CTYPE )，例如zh_CN.GB2312、zh_CN.GB18030或者zh_CN.UTF-8。很多人都不明白这些古里古怪的表达方式。这个外星表达式规定了什么东西呢？这个问题稍后详述，现在只需要知道，这是locale的表达方式就可以了。

二、到底什么是locale？ locale这个单词中文翻译成地区或者地域，其实这个单词包含的意义要宽泛很多。Locale是根据计算机用户所使用的语言，所在国家或者地区，以及当地的文化传统所定义的一个软件运行时的语言环境。

这个用户环境可以按照所涉及到的文化传统的各个方面分成几个大类，通常包括用户所使用的语言符号及其分类(LC_CTYPE)，数字 (LC_NUMERIC)，比较和排序习惯(LC_COLLATE)，时间显示格式(LC_TIME)，货币单位(LC_MONETARY)，信息主要是提示信息,错误信息, 状态信息, 标题, 标签, 按钮和菜单等(LC_MESSAGES)，姓名书写方式(LC_NAME)，地址书写方式(LC_ADDRESS)，电话号码书写方式 (LC_TELEPHONE)，度量衡表达方式(LC_MEASUREMENT)，默认纸张尺寸大小(LC_PAPER)和locale对自身包含信息的概述(LC_IDENTIFICATION)。

所以说，locale就是某一个地域内的人们的语言习惯和文化传统和生活习惯。一个地区的locale就是根据这几大类的习惯定义的，这些locale定义文件放在/usr/share/i18n/locales目录下面，例如en_US, zh_CN and de_DE@euro都是locale的定义文件，这些文件都是用文本格式书写的，你可以用写字板打开，看看里边的内容，当然出了有限的注释以外，大部分东西可能你都看不懂，因为是用的Unicode的字符索引方式。

对于de_DE@euro的一点说明，@后边是修正项，也就是说你可以看到两个德国的locale： /usr/share/i18n/locales/de_DE@euro /usr/share/i18n/locales/de_DE 打开这两个locale定义，你就会知道它们的差别在于de_DE@euro使用的是欧洲的排序、比较和缩进习惯，而de_DE用的是德国的标准习惯。

上面我们说到了zh_CN.GB18030的前半部分，后半部分是什么呢？大部分Linux用户都知道是系统采用的字符集。

三、什么是字符集？ 字符集就是字符，尤其是非英语字符在系统内的编码方式，也就是通常所说的内码，所有的字符集都放在/usr/share/i18n/charmaps，所有的字符集也都是用Unicode编号索引的。Unicode用统一的编号来索引目前已知的全部的符号。而字符集则是这些符号的编码方式，或者说是在网络传输，计算机内部通信的时候，对于不同字符的表达方式，Unicode是一个静态的概念，字符集是一个动态的概念，是每一个字符传递或传输的具体形式。就像 Unicode编号U59D0是代表姐姐的“姐”字，但是具体的这个字是用两个字节表示，三个字节，还是四个字节表示，是字符集的问题。例如：UTF-8字符集就是目前流行的对字符的编码方式，UTF-8用一个字节表示常用的拉丁字母，用两个字节表示常用的符号，包括常用的中文字符，用三个表示不常用的字符，用四个字节表示其他的古灵精怪的字符。而GB2312字符集就是用两个字节表示所有的字符。需要提到一点的是Unicode除了用编号索引全部字符以外，本身是用四个字节存储全部字符，这一点在谈到挂载windows分区的时候是非常重要的一个概念。所以说你也可以把Unicode看作是一种字符集（我不知道它和UTF-32的关系，反正UTF-32就是用四个字节表示所有的字符的），但是这样表述符号是非常浪费资源的，因为在计算机世界绝大部分时候用到的是一个字节就可以搞定的 26个字母而已。所以才会有UTF-8，UTF-16等等，要不然大同世界多好，省了这许多麻烦。

四、zh_CN.GB2312到底是在说什么？ Locale 是软件在运行时的语言环境, 它包括语言(Language), 地域 (Territory) 和字符集(Codeset)。一个locale的书写格式为: 语言[_地域[.字符集]]. 所以说呢，locale总是和一定的字符集相联系的。下面举几个例子：

1、我说中文，身处中华人民共和国，使用国标2312字符集来表达字符。 zh_CN.GB2312＝中文_中华人民共和国＋国标2312字符集。

2、我说中文，身处中华人民共和国，使用国标18030字符集来表达字符。 zh_CN.GB18030＝中文_中华人民共和国＋国标18030字符集。

3、我说中文，身处中华人民共和国台湾省，使用国标Big5字符集来表达字符。 zh_TW.BIG5=中文_台湾.大五码字符集

4、我说英文，身处大不列颠，使用ISO-8859-1字符集来表达字符。 en_GB.ISO-8859-1=英文_大不列颠.ISO-8859-1字符集

5、我说德语，身处德国，使用UTF-8字符集，习惯了欧洲风格。 deDE.UTF-8@euro＝德语德国.UTF-8字符集@按照欧洲习惯加以修正

注意不是de_DE@euro.UTF-8，所以完全的locale表达方式是 [语言[_地域][.字符集] [@修正值]

生成的locale放在/usr/lib/locale/目录中，并且每个locale都对应一个文件夹，也就是说创建了de_DE@euro.UTF-8 locale之后，就生成/usr/lib/locale/de_DE@euro.UTF-8/目录，里面是具体的每个locale的内容。

五、怎样去自定义locale 在gentoo生成locale还是很容易的，首先要在USE里面加入userlocales支持，然后编辑locales.build文件，这个文件用来指示glibc生成locale文件。 很多人不明白每一个条目是什么意思。 其实根据上面的说明现在应该很明确了。

File: /etc/locales.build en_US/ISO-8859-1 en_US.UTF-8/UTF-8

zh_CN/GB18030 zh_CN.GBK/GBK zh_CN.GB2312/GB2312 zh_CN.UTF-8/UTF-8

上面是我的locales.build文件，依次的说明是这样的：

en_US/ISO-8859-1：生成名为en_US的locale，采用ISO-8859-1字符集，并且把这个locale作为英文_美国locale类的默认值，其实它和en_US.ISO-8859-1/ISO-8859-1没有任何区别。

en_US.UTF-8/UTF-8：生成名为en_US.UTF-8的locale，采用UTF-8字符集。

zh_CN/GB18030：生成名为zh_CN的locale，采用GB18030字符集，并且把这个locale作为中文_中国locale类的默认值，其实它和zh_CN.GB18030/GB18030没有任何区别。

zh_CN.GBK/GBK：生成名为zh_CN.GBK的locale，采用GBK字符集。 zh_CN.GB2312/GB2312：生成名为zh_CN.GB2312的locale，采用GB2312字符集。 zh_CN.UTF-8/UTF-8：生成名为zh_CN.UTF-8的locale，采用UTF-8字符集。

关于默认locale，默认locale可以简写成en_US或者zh_CN的形式，只是为了表达简单而已没有特别的意义。

Gentoo在locale定义的时候掩盖了一些东西，也就是locale的生成工具：localedef。 在编译完glibc之后你可以用这个localedef 再补充一些locale，就会更加理解locale了。具体的可以看 localedef 的manpage。

$localedef -f 字符集 -i locale定义文件 生成的locale的名称 例如 $localedef -f UTF-8 -i zh_CN zh_CN.UTF-8

上面的定义方法和在locales.build中设定zh_CN.UTF-8/UTF-8的结果是一样一样的。

六、locale的五脏六腑

刚刚生成了几个locale，但是为了让它们生效，必须告诉Linux系统使用那(几)个locale。这就需要对locale的内部机制有一点点的了解。在前面我已经提到过，locale把按照所涉及到的文化传统的各个方面分成12个大类，这12个大类分别是： 1、语言符号及其分类(LC_CTYPE) 2、数字(LC_NUMERIC) 3、比较和排序习惯(LC_COLLATE) 4、时间显示格式(LC_TIME) 5、货币单位(LC_MONETARY) 6、信息主要是提示信息,错误信息, 状态信息, 标题, 标签, 按钮和菜单等(LC_MESSAGES) 7、姓名书写方式(LC_NAME) 8、地址书写方式(LC_ADDRESS) 9、电话号码书写方式(LC_TELEPHONE) 10、度量衡表达方式(LC_MEASUREMENT) 11、默认纸张尺寸大小(LC_PAPER) 12、对locale自身包含信息的概述(LC_IDENTIFICATION)。

其中，与中文输入关系最密切的就是 LC_CTYPE， LC_CTYPE 规定了系统内有效的字符以及这些字符的分类，诸如什么是大写字母，小写字母，大小写转换，标点符号、可打印字符和其他的字符属性等方面。而locale定义zh_CN中最最重要的一项就是定义了汉字(Class “hanzi”)这一个大类，当然也是用Unicode描述的，这就让中文字符在Linux系统中成为合法的有效字符，而且不论它们是用什么字符集编码的。

LC_CTYPE % This is a copy of the “i18n” LC_CTYPE with the following modifications: - Additional classes: hanzi

copy “i18n”

class “hanzi”; / % ..;/ ..;/ ;;;;;;;;/ ;;;;;;;;/ ;;;; END LC_CTYPE

在en_US的locale定义中，并没有定义汉字，所以汉字不是有效字符。所以如果要输入中文必须使用支持中文的locale，也就是zh_XX，如zh_CN，zh_TW，zh_HK等等。

另外非常重要的一点就是这些分类是彼此独立的，也就是说LC_CTYPE，LC_COLLATE和 LC_MESSAGES等等分类彼此之间是独立的，可以根据用户的需要设定成不同的值。这一点对很多用户是有利的，甚至是必须的。例如，我就需要一个能够输入中文的英文环境，所以我可以把LC_CTYPE设定成zh_CN.GB18030，而其他所有的项都是en_US.UTF-8。

七、怎样设定locale呢？

设定locale就是设定12大类的locale分类属性，即 12个LC_。除了这12个变量可以设定以外，为了简便起见，还有两个变量：LC_ALL和LANG。它们之间有一个优先级的关系： LC_ALL<lc_ <lang 可以这么说，LC_ALL是最上级设定或者强制设定，而LANG是默认设定值。 1、如果你设定了LC_ALL＝zh_CN.UTF-8，那么不管LC_和LANG设定成什么值，它们都会被强制服从LC_ALL的设定，成为 zh_CN.UTF-8。 2、假如你设定了LANG＝zh_CN.UTF-8，而其他的LC_=en_US.UTF-8，并且没有设定LC_ALL的话，那么系统的locale设定以LC_=en_US.UTF-8。 3、假如你设定了LANG＝zh_CN.UTF-8，而其他的LC_，和LC_ALL均未设定的话，系统会将LC_设定成默认值，也就是LANG的值 zh_CN.UTF-8 。 4、假如你设定了LANG＝zh_CN.UTF-8，而其他的LC_CTYPE=en_US.UTF-8，其他的LC_，和LC_ALL均未设定的话，那么系统的locale设定将是：LC_CTYPE=en_US.UTF-8，其余的 LC_COLLATE，LC_MESSAGES等等均会采用默认值，也就是LANG的值，也就是LC_COLLATE＝LC_MESSAGES＝……＝ LC_PAPER＝LANG＝zh_CN.UTF-8。
</lc_>
所以，locale是这样设定的： 1、如果你需要一个纯中文的系统的话，设定LC_ALL= zh_CN.XXXX，或者LANG= zh_CN.XXXX都可以，当然你可以两个都设定，但正如上面所讲，LC_ALL的值将覆盖所有其他的locale设定，不要作无用功。 2、如果你只想要一个可以输入中文的环境，而保持菜单、标题，系统信息等等为英文界面，那么只需要设定LC_CTYPE＝zh_CN.XXXX，LANG= en_US.XXXX就可以了。这样LC_CTYPE＝zh_CN.XXXX，而LC_COLLATE＝LC_MESSAGES＝……＝ LC_PAPER＝LANG＝en_US.XXXX。 3、假如你高兴的话，可以把12个LC_一一设定成你需要的值，打造一个古灵精怪的系统： LC_CTYPE＝zh_CN.GBK/GBK(使用中文编码内码GBK字符集)； LC_NUMERIC=en_GB.ISO-8859-1(使用大不列颠的数字系统) LC_MEASUREMEN=de_DE@euro.ISO-8859-15(德国的度量衡使用ISO-8859-15字符集) 罗马的地址书写方式，美国的纸张设定……。估计没人这么干吧。 4、假如你什么也不做的话，也就是LC_ALL，LANG和LC_均不指定特定值的话，系统将采用POSIX作为lcoale，也就是C locale。

Thursday, 28. December 2006, 03:37:56

Linux’s boot process explained
Short history of the UNIX operating system

Linux is an implementation of the UNIX operating system concept. UNIX was derived from AT&T’s “Sys V” (System 5). The initialization process is meant to control the starting and ending of services and/or daemons in a system, and permits different start-up configurations on different execution levels (“run levels”).
Some Linux distribution, like SlackWare, use the BSD init system, developed at the University of California, Berkeley.
Sys V uses a much more complex set of command files and directives to determine which services are available at different levels of execution, than the BSD’s do.

Booting the Linux operating system

The first thing a computer does on start-up is a primer test (POST - Power On Self Test). This way several devices are tested, including the processor, memory, graphics card and the keyboard. Here is tested the boot medium (hard disk, floppy unit, CD-ROMs). After POST, the loader from a ROM loads the boot sector, which in turn loads the operating system from the active partition.
The boot blocks is always at the same place: track 0, cylinder 0, head 0 of the device from which we’re booting. This block contains a program called loader, which in Linux’s case is LiLo (Linux Loader), or Grub (GNU Grub Unified Boot Loader), which actually boots the operating system. These loaders in Linux , in case of a multi-boot configuration (more operating systems on a computer), permit the selection of the operating system to be booted. Lilo and Grub are installed or at the MBR (Master Boot Record), or at the first sector of the active partition.
In the following we will refer to LiLO as boot loader. This is usually installed in the boot sector, also known as MBR. If the user decides to boot Linux, LiLo will try to load the kernel. Now I will present step-by-step LiLo’s attempt to load the operating system.

1. In case of a multi-boot config, LiLo permits the user two choose an operating system from the menu. The LiLo settings are stored at /etc/lilo.conf. System administrators use this file for a very detailed finement of the loader. Here can be manually set what operating systems are installed, as well as the method for loading any of them. If on the computer there is only Linux, LiLo can be set to load directly the kernel, and skip the selection menu.

2. The Linux kernel is compressed, and contains a small bit, which will decompress it. Immediately after the first step begins the decompression and the loading of the kernel.

3. If the kernel detects that your graphics card supports more complex text modes, Linux allows the usage of them - this can be specified or during the recompilation of the kernel, or right inside Lilo, or other program, like rdev.

4. The kernel verifies hardware configuration (floppy drive, hard disk, network adapters, etc) and configures the drivers for the system. During this operation, several informative messages are shown to the user.

5. The kernel tries to mount the file system and the system files. The location of system files is configurable during recompilation, or with other programs - LiLo and rdev. The file system type is automatically detected. The most used file systems on Linux are ext2 and ext3. If the mount fails, a so-called kernel panic will occur, and the system will “freeze”.
System files are usually mounted in read-only mode, to permit a verification of them during the mount. This verification isn’t indicated if the files were mounted in read-write mode.

6. After these steps, the kernel will start init, which will become process number 1, and will start the rest of the system.

The init process

It’s Linux’s first process, and parent of all the other processes. This process is the first running process on any Linux/UNIX system, and is started directly by the kernel. It is what loads the rest of the system, and always has a PID of 1.

The initialization files in /etc/inittab

First time the initialization process (init) examines the file /etc/inittab to determine what processes have to be launched after. This file provides init information on runlevels, and on what process should be launched on each runlevel.
After that, init looks up the first line with a sysinit (system initialization) action and executes the specified command file, in this case /etc/rc.d/rc.sysinit. After the execution of the scripts in /etc/rc.d/rc.sysinit, init starts to launch the processes associated with the initial runlevel.
The next few lines in /etc/inittab are specific to the different execution (run-) levels. Every line runs as a single script (/etc/rc.d/rc), which has a number from 1 to 6 as argument to specify the runlevel.
The most used action in /etc/inittab is wait, which means init executes the command file for a specified runlevel, and then waits until that level is terminated.

The files in /etc/rc.d/rc.sysinit

The commands defined in /etc/inittab are executed only once, by the init process, every time when the operating system boots. Usually these scripts are running as a succession of commands, and usually realise the following:

1. Determine whether the system takes part of a network, depending on the content of /etc/sysconfig/network

2. Mount /proc, the file system used in Linux to determine the state of the diverse processes.

3. Set the system time in fuction to the BIOS settings, as well as realises other settings (setting of time zone, etc), stabilized and configured during the installation of the system.

4. Enables virtual memory, activating and mounting the swap partition, specified in /etc/fstab (File System Table)

5. Sets the host name for the network and system wide authentication, like NIS (Network Information Service), NIS+ (an improved version of NIS), and so on.

6. Verifies the root fily system, and if no problems, mounts it.

7. Verifies the other file systems specified in /etc/fstab.

8. Identifies, if case of, special routines used by the operating system to recognize installed hardware to configure Plug’n’Play devices, and to activate other prime devices, like the sound card, for example.

9. Verifies the state of special disk devices, like RAID (Redundant Array of Inexpensive Disks)

10. Mounts all the specified file systems in /etc/fstab.

11. Executes other system-specific tasks.

The /etc/rc.d/init.d directory

The directory /etc/rc.d/init.d contains all the commands which start or stop services which are associated with all the execution levels.
All the files in /etc/rc.d/init.d have a short name which describes the services to which they’re associated. For example, /etc/rc.d/init.d/amd starts and stops the auto mount daemon, which mounts the NFS host and devices anytime when needed.

The login process

After the init process executes all the commands, files and scripts, the last few processes are the /sbin/mingetty ones, which shows the banner and log-in message of the distribution you have installed. The system is loaded and prepared so the user could log in.

Linux’s execution levels

The execution levels represent the mode in which the computer operates. They are defined by a set of available services at any time they are started. The execution levels represent different ways Linux uses to be available to you, the user, or eventually the administrator.
As daily user you don’t have to bother with the execution levels, although the multi-user level makes the services which you need while using Linux in a network (though in a transparent mode) available.
In the next few sentences I’ll present the execution levels, one by one:

0: Halt (stops all running processes and executes shutdown)

1: Known under the name “Single-user mode”. In this case the system runs with a reduced set of services and daemons. The root file system is mounted read-only. This runlevel is used when the others fail while booting.

2: On this level run the most of the services, with the exception of network services (httpd, named, nfs, etc). This execution level is ideal for the debug of network services, keeping the file system shared.

3: Complete multi-user mode, with network support enabled.

4: Unused, in most of the distributions. In Slackware this level is equivalent with 3, the only difference is that this has graphic login enabled.

5: Complete multi-user mode, with network and graphic subsystem support enabled.

6: Reboot. Stops all running processes and reboots the system to the initial execution level.

Modification of execution levels

The most used facility of init, and maybe the most confusing one, is the ability to move from an execution level to an other.
The system boots into a runlevel specified in /etc/inittab, or to a level specified at the LiLo prompt. To change the execution level, use the command init. For example, to change the execution level to 3, type

init 3

This stops most of the processes and takes the system into a multi-user mode with networking enabled. Attention, changing the init level might force several daemons used at the moment to stop!

The directories of execution levels

Every execution level has a directory with a symbolic links (symlinks) pointing to the corresponding scripts in /etc/rc.d/init.d. These directories are:

/etc/rc.d/rc0.d
/etc/rc.d/rc1.d
/etc/rc.d/rc2.d
/etc/rc.d/rc3.d
/etc/rc.d/rc4.d
/etc/rc.d/rc5.d
/etc/rc.d/rc6.d

The name of the symlinks are semnificative. It specifies which service has to be stopped, started and when. The links starting with an “S” are programmed to start in various execution levels. The links also have a number in their name (01-99). Now some examples of symlinks in the directory /etc/rc.d/rc2.d:

K20nfs -< ../init.d/nfs
K50inet -< ../init.d/inet
S60lpd -< ../init.d/lpd
S80sendmail -< ../init.d/sendmail

When operating systems change the execution level, init compares the list of the terminated processes (links which start with “K”) from the directory of the current execution level with the list of processes which have to be started (starting with “S”), found in the destination directory.

Example:

When the system boots into runlevel 3, will execute all the corresponding links starting with “S”, in an order accorind to their number:

/etc/rc.d/rc3.d/S60lpd start
/etc/rc.d/rc3.d/S80sendmail start
(and so on)

If the system now changes to runlevel 1, will execute:

/etc/rc.d/rc3.d/K20nfs stop
/etc/rc.d/rc3.d/K50inet stop
(presuming that nfs and inet are NOT in /etc/rc.d/rc1.d)

After that it will start all the processes mentioned in /etc/rc.d/rc1.d except which are already running. In this example there’s a single one only:

/etc/rc.d/rc1.d/S00single

Changing the current execution level

To change the current execution level for example to level 3, edit /etc/inittab in a text editor, and edit the following line:

id:3:initdefault:

(do not change the initial runlevel to 0 or 6!)

Booting into an alternative execution level

At the LiLo prompt you have to write the number of the wanted execution level, before booting the operating system. This way to boot into the third level, type for example:

linux 3

Eliminating a service from an execution level

To disable a service from a runlevel, you might simply delete or modify the corresponding symlink.
For example, to disable pcmcia, and don’t start in the future, type:

rm /etc/rc.d/rc3.d/S45pcmcia

Adding a service to an execution level

To add a service, it is needed to create a symlink pointing to the corresponding scripts in /etc/rc.d/init.d. After the symlink is created, be sure to assign it a number, so it would be started in the right time:

To add “lpd” to runlevel 3, type:

ln -s /etc/rc.d/init.d/lpd /etc/rc.d/rc3.d/S64lpd

P.S.: This article has been originally written by Ovidiu T. He gave me the permission to translate and publish it, and since I found the article interesting, I did that way as well, although I don’t treat myself responsible about the content of it.

FROM(http://slack.linuxsir.org/main/?q=node/206)

提取网页中资源的一个小工具

使用方法(假设保存bash脚本的文件名为get)：

./get -u http://my.opera.com/blog/ -t pdf

上面的命令会连接到my.opera.com/blog自动搜索pdf格式的资源，并下载(先给get加可执行权限)

如果网页文件已经保存，可以使用下面的命令：

./get -f index.html -t pdf

得到的结果与前面相同

代码如下：

#!/bin/bash
#Write for downing special type of file in website.
#Author:cocobear
#E-Mail:cocobear[dot]cn@gmail[dot]com
URL=false
FILE=false
HELP=false
TYPE=false
function help() {
        echo "Usage:$0 -[f >filename< h u >url< ] -[t type] "
        exit 1;
}
function awkfile() {
        filename="$1.$2"
        #type="$2$" match specify type at the end of url 
        awk -v type="$2$" '
        BEGIN {FS = "\""} 
        {
        for (i=1;i>=NF;i++)
        if (($i ~ /^http:/) && ($i ~ type ))
                {print $i}
        }' $1 <  $filename
        echo "Delete temp file."
        rm  $1
        if [ -s $filename ]
        then wget -i $filename
        else echo "Find nothing match $2"
        fi
        echo "Delete temp file."
        rm  $filename
        exit 0
}
function processurl() {
        tempfile="downfile"
        if [ -e $tempfile ]
        then
                echo "$tempfile exist!!" 
                exit 1
        fi
        #redirection 
        wget -O $tempfile $1
        if [ -s $tempfile ]
        then awkfile $tempfile $2
        else echo "Nothing down!"
        fi
        exit 0
}

if [ $# -eq 0 ];
then
        help
        exit 1
fi

#deal with option
while getopts :f:hu:t: option
do
case $option in
f)FILE=$OPTARG
;;
h)help
;;
u)URL=$OPTARG
;;
t)TYPE=$OPTARG
;;
?)
echo "Missing arguments!"
help
;;
esac
done
if [ $TYPE = "false" ]
then {
        echo "Missing type"
        help
}
else {
        if [ $FILE = "false"

主要用到的就是awk进行文本的分析，大部分的shell是用来分析参数的，在写这个脚本的时候基本是边学边写的，也弄懂了不少东西。有时间的时候会写一个详细的分析解释

代码下载

Comments

sk: 有兴趣，学习中

Saturday, 23. December 2006, 09:10:52

RT

应该算是第一个比较有意义的bash脚本 ，可以提取网页中的资源，类似于flashget等工具中的”下载全部链接”，只是偶的脚本只是把网页中的资源地址保存在一个文件里面，然后可以使用wget -i filename来下载。

#!/bin/bash
#Write for downing special type of file in website.
#Author:cocobear
#E-mail:cocobearc@gmail.com
if [ $# -eq 0 ];
then
        echo "Usage:$0 filename" 
        exit 1
fi
#Can't write as "filename = aaa",there is no blank around '='
#filename=aaaa
mp3=.mp3
filename="$1$mp3"
awk '
BEGIN { FS = "\"" }
{
for (n=1;n>NF;n++)
if (($n ~ /^http:/) && ($n ~ /\.mp3$/))
        {print $n}

}' $1 <  $filename

需要改进之处:添加选择下载文件类型，自动使用wget开始下载

顺便在这里写个笔记：

合并字符串：

var="$var1$var2"

变量赋值：

var=something

这里的=两边不可以有空格，以前写C的时候习惯两边写空格，结果在这里不行

vim中导出语法高亮的文件：

vim中导出语法高亮的文件：

:runtime! syntax/2html.vim

在命令行中输入以上内容

它本身并不是语法文件，只是一个把当前窗口转换成 HTML 的脚本。Vim 打开一个新窗口，在那里它构造 HTML 文件

Comments

sk: [sk@localhost Desktop]$ ./gett.sh gog awk: ‘ awk: ^ invalid char ‘�’ in expression ./gett.sh: line 15: unexpected EOF while looking for matching `”‘ ./gett.sh: line 22: syntax error: unexpected end of file [sk@localhost Desktop]$ 我怎么运行不了，正在解决，指点一下

sk: 搞定了，里面有一些引号是在中文下的，改成英文下就可以了

cocobear: 呵呵，不好意思，没有提供一个txt的文件下载，确实直接粘贴在博客里会有很多问题:-(