├── .gitignore ├── LICENSE ├── README.md ├── SUMMARY.md ├── book.json └── content ├── auth.md ├── file-system.md ├── history.md ├── install_rpm_and_source.md ├── monitor.md ├── process.md ├── rsync.md ├── shell.md ├── ssh.md ├── system-log.md ├── systemd.md ├── vim.md └── xargs.md /.gitignore: -------------------------------------------------------------------------------- 1 | # Node rules: 2 | ## Grunt intermediate storage (http://gruntjs.com/creating-plugins#storing-task-files) 3 | .grunt 4 | 5 | ## Dependency directory 6 | ## Commenting this out is preferred by some people, see 7 | ## https://docs.npmjs.com/misc/faq#should-i-check-my-node_modules-folder-into-git 8 | node_modules 9 | 10 | # Book build output 11 | _book 12 | 13 | # eBook build output 14 | *.epub 15 | *.mobi 16 | *.pdf 17 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Web开发者手边的一本CentOS小书 2 | 这本 CentOS 小书是对 CentOS 系统知识的一个整理以及补完，当然对于其它 Linux 发行版本也有很大的参考意义，但的确针对的是目前 CentOS 的最新版本——**CentOS 7** 3 | 4 | ## 注意 5 | 虽然本书打着*整理补完*的旗号，但毕竟只是一本小书，肯定是比不上外面那些大部头的。因此，本书的着重点是一名web开发人员所需要的知识体系。另外，对于一些必要的概念、或是不常用的命令，书中仅提供搜索关键词，作为知识索引提供诸君参考。 6 | -------------------------------------------------------------------------------- /SUMMARY.md: -------------------------------------------------------------------------------- 1 | # Summary 2 | 3 | * [封面](README.md) 4 | * [第一章：CentOS的系统服务管理系统](content/systemd.md) 5 | * [第二章：CentOS的文件系统](content/file-system.md) 6 | * [第三章：CentOS的进程系统](content/process.md) 7 | * [第四章：CentOS的系统用户与用户组管理](content/auth.md) 8 | * [第五章：Vim的使用](content/vim.md) 9 | * [第六章：安装RPM包或源码包](content/install_rpm_and_source.md) 10 | * [第七章：shell相关](content/shell.md) 11 | * [第八章：神奇的xargs命令](content/xargs.md) 12 | * [第九章：CentOS的历史命令](content/history.md) 13 | * [第十章：监控CentOS的系统状态](content/monitor.md) 14 | * [第十一章：SSH远程登录](content/ssh.md) 15 | * [第十二章：备份工具rsync](content/rsync.md) 16 | * [第十三章：Linux系统日志](content/system-log.md) -------------------------------------------------------------------------------- /book.json: -------------------------------------------------------------------------------- 1 | { 2 | "author": "Array-Huang ", 3 | "title": "CentOS小书", 4 | "description": "这本 CentOS 小书是对 CentOS 系统知识的一个整理以及补完，当然对于其它 Linux 发行版本也有很大的参考意义，但的确针对的是目前 CentOS 的最新版本——CentOS 7", 5 | "generator": "site", 6 | "links": { 7 | "sidebar": { 8 | "作者博客": "https://segmentfault.com/u/array_huang" 9 | } 10 | } 11 | } -------------------------------------------------------------------------------- /content/auth.md: -------------------------------------------------------------------------------- 1 | # 第四章：CentOS的系统用户与用户组管理 2 | 3 | ## 更改文件或文件目录的权限 4 | - `groupadd` 增加一个用户组 5 | - `chgrp` 更改所属组 6 | - `chown` 更改所属主，除了可以更改所属用户外，还可更改所属组 7 | - `chmod` 改变用户对文件的读写执行权限，如744 8 | - `umask` 改变新建文件/目录的默认读写执行权限 9 | 10 | ## 如何创建一个不允许登录的账号(仅供某个后台服务使用) 11 | ``` 12 | useradd -M -s /sbin/nologin nologinUser 13 | ``` 14 | 但需要注意的是： 15 | - `/sbin/nologin`只是不允许系统login，可以使用其他ftp等服务。 16 | - 如果想彻底一点什么服务都禁止掉，可以使用`/bin/false`。 17 | 18 | ## 为系统设置管理员账号，避免使用root账号造成误操作 19 | - 非root用户可使用`sudo`命令来执行本来只能由root用户才能执行的命令。 20 | - 并非所有的非root用户都可以使用`sudo`命令，只有在`/etc/sudoers`里指定的用户才有此能力。 21 | - 授权使用`sudo`命令的用户，需要root用户使用`visudo`命令进行编辑。 22 | - 为方便起见，可以设置一个“管理员用户组”，先授权这个用户组使用`sudo`命令，再把管理员用户的账号加入到这个“管理员用户组”中即可。授权用户组的配置如下：`%wheel ALL=(ALL) ALL`；这个配置便授权给了`wheel`这个用户组。 23 | 24 | ## 添加或删除某个用户组的成员 25 | - 查`gpasswd`。 26 | - 如果图省事，想一次性让某个用户加入多个用户组，可以使用`usermod`。 -------------------------------------------------------------------------------- /content/file-system.md: -------------------------------------------------------------------------------- 1 | # 第二章：CentOS的文件系统 2 | 3 | ## 修改文件的特殊属性 4 | `chattr`，可修改文件的多种特殊属性： 5 | - `a`，增加该属性后，只能追加不能删除，非root用户不能设定该属性 6 | - `c`，自动压缩该文件，读取时会自动解压； 7 | - `i`，增加后，使文件不能被删除、重命名、设定链接接、写入、新增数据 8 | 9 | `lsattr`，该命令用来读取文件或者目录的特殊权限 10 | 11 | ## 在linux下搜一个文件 12 | - `which`，找命令。 13 | - `locate`，针对已生成的全局文件树索引对文件名进行搜索，但使用前需要先安装`mlocate`且执行`updatedb`来生成文件树索引；该命令仅支持按文件名进行搜索。 14 | - `find`，遍历查找指定目录（不指定就针对整个系统进行查找）；该命令支持多种筛选条件（可按`与或否`的逻辑关系进行串联）进行查找，如： 15 | - 文件名，通过`-name`和`-iname`参数传入，支持通配符。 16 | - 所属用户，通过`-user`参数传入。 17 | - 所属组，通过`-group`参数传入。 18 | - 文件时间戳的相关属性，通过`-atime`(Access time)/`-ctime`(Change time)/`-mtime`(Modify time)参数传入，其中`-mtime`参数比较常用。 19 | - 文件类型，通过`-type`参数传入。 20 | - 文件大小，通过`-size`参数传入。 21 | 22 | ## 如何动态显示一个不停增加内容的文件 23 | - 使用`tail -f`可实时追踪一个或多个文档的所有更新，这个功能在调试程序时非常好用： 24 | ``` 25 | tail -f /var/log/mail.log /var/log/apache/error_log 26 | ``` 27 | 28 | ## 查看文件/目录占用磁盘大小 29 | `du -sh filename`，解释： 30 | - `-s`，表示只列出目录本身的数据。 31 | - `-h`，系统自动调节单位。 32 | 33 | ## 压缩和解压缩 34 | ### gzip 压缩工具 35 | - linux下压缩工具有多种，但最常用的是gzip，其它的使用起来也差不多。 36 | - gzip只支持文件的压缩，若要压缩目录，则需要使用下述的`tar`打包工具。 37 | - 压缩直接用`gzip sourcefile`，解压则用`gzip -d zipfile`。 38 | - 使用 gzip 压缩的文件后缀一般为`.gz`。 39 | 40 | ### tar 打包工具 41 | - tar 本身是一个打包工具，并不具有压缩功能，但可以配合压缩工具，一次性完成打包和压缩的任务；通常情况下我们也不会只打包不压缩，所以我们直接记住“一次性打包压缩”的参数即可： 42 | - `tar -czvf distfile sourcedir`，压缩打包sourcedir到disfile。 43 | - `tar -zxvf sourcefile`，解压解包fourcefile到当前目录。 44 | - 解释一下上面命令用到的参数： 45 | - `-z`表示使用 gzip 压缩工具；其实还可使用其它压缩工具（如 bzip2 和 xz），但毕竟最常用的还是 gzip。 46 | - `-c`(`c` for compress)表示压缩打包，`-x`表示解压解包。 47 | - `-v`表示可视化。 48 | - `-f`后面跟文件名（即`-f filename`），表示压缩后的文件名为 filename，或当期需要解压文件 filename。 49 | - tar 除了可以打包目录，还可以指定多个文件打包到一起：`tar -czvf files.tar.gz file1 file2 file3`。 50 | - tar 命令支持查看（但不解压）压缩文件的内容，其参数为`-t`，但需要注意的是必须与`-f`同用，其用法为：`tar -tf file.tar.gz`。 51 | 52 | ### zip 压缩工具 53 | - 对比起上述介绍的 gzip 和 tar，zip 的功能更为强大，它可以压缩(解压)文件和目录。 54 | - 由于 zip 在 windows 系统上比较常用，因此如需与 windows 系统交换文件，可通过 zip 进行压缩，这样两边都可以识别。 55 | - CentOS 默认不带 zip 命令，需要通过`yum install -y zip`进行安装。 56 | - 压缩文件用`zip distfile sourcefile`，压缩目录则用`zip distfile sourcedir`。 57 | - 需要注意的是，当压缩目录下还有二级目录甚至更多级目录时，zip 命令仅仅是把二级目录本身压缩而已，如果想要一并压缩二级目录下的文件及更多级目录，则必须加上`-r`，如`zip -r distfile sourcedir`。 58 | - 解压文件并不用 zip 命令，而是用`unzip`命令，如`unzip file.zip`。 59 | - 除了基本的压缩/解压功能外，zip 还提供更多进阶功能，如：使用密码进行加密；设置压缩级别；添加注释，等等。 -------------------------------------------------------------------------------- /content/history.md: -------------------------------------------------------------------------------- 1 | # 第九章：CentOS的历史命令 2 | 3 | ## 查看（只读）文件内容或其它linux命令执行结果 4 | 实例：查看命令历史使用记录并通过less分页显示，命令：`history | less` 5 | 6 | ## 重新执行历史命令 7 | Linux会把我们执行过的命令记录起来，预设可以记录1000条历史记录，这些记录保存在用户家目录的`.bash_history`文件中。 8 | - 一般来说，我们可以通过按动方向键上下来选择过往执行过的命令，但如果太久远的命令要找就太繁琐了，此时我们便可以充分利用这历史命令记录：先利用`history`找到想重新执行的命令的编号，比如说编号为101的命令为`pwd`，然后再输入`!101`，这样就相当于我们执行了一遍`pwd`命令。 9 | - 另外我们还可以通过`!!`来直接执行上一条命令，不过当然我还是倾向于按方向键上来找到上一条命令。 -------------------------------------------------------------------------------- /content/install_rpm_and_source.md: -------------------------------------------------------------------------------- 1 | ## RPM(Red Hat Package Manager) 2 | - 系统中存在着一个关于RPM的数据库，它记录了安装包以及包与包之间的依赖关系。 3 | - RPM包是预先在Linux机器上编译并打包的文件，安装非常快捷；但它也有一些缺点： 4 | - 安装环境必须与编译时的环境一致或者相当； 5 | - 包与包之间存在着相互依赖的情况下，卸载某个包时，需要先把系统里所有依赖该包的包进行卸载；虽然也可忽略依赖关系进行强制删除，但这样就会导致异常情况的发生。 6 | - 安装RPM包使用命令`rpm -ivh filename`，其中： 7 | - `-i`，表示安装； 8 | - `-v`，表示可视化； 9 | - `-h`，表示显示安装进度； 10 | - 升级RPM包使用命令`rpm -Uvh filename`，其中的`-U`就表示升级。 11 | - 查询rpm包： 12 | - 查询是否已安装某个包使用命令`rpm -q packagename`，如`rpm -q zip`。另外，我们可以通过`rpm -qa`的命令来查询系统中所有已安装的包，并通过`grep`等方式进行二次搜索，如`rpm -qa | grep zip`。 13 | - 查询某个已安装的RPM包的详情：`rpm -qi packagename`，可得到版本号、安装时间、简介等信息。 14 | - 卸载RPM包使用命令为`rpm -e packagename`。 15 | 16 | ## yum 工具 17 | - Yum(Yellow dog Updater,Modified)是一个在Fedora和RedHat以及CentOS中的Shell前端软件包管理器。基于RPM包管理，能够从指定的服务器自动下载RPM包并且安装，可以自动处理依赖性关系，并且一次安装所有依赖的软件包，无须繁琐地一次次下载、安装。 18 | - 列出所有可用的RPM包：`yum list`，由于数量众多，我们一般会进行二次搜索、筛选，如`yum list | grep zip | head -n 5`；此命令列出的信息里，主要有以下三列： 19 | - 第一列是包名，含平台信息。 20 | - 第二列是最新版本号。 21 | - 第三列是安装信息，如果已安装，则显示`@base`或`@anaconda`;如果未安装则显示`base`或`anaconda`；如果已安装但已有更新版本，则显示`updates`。 22 | - 搜索RPM包的命令是`yum search str`，如`yun search zip`。 23 | - 安装RPM包的命令是`yum install -y packagename`，如`yun install -y zip`，需要注意的是，虽然不加`-y`也是可以正常安装RPM包的，但是不加`-y`的话，如果该RPM包有依赖的包，就会一个一个轮流询问用户是否需要安装，那样子就太繁琐了，不如就加个`-y`全部默认安装，这也正是 yum 的一大特点嘛。 24 | - 卸载RPM包的命令为`yum remove -y packagename`，加`-y`的原因同`yum install`。 25 | - 升级RPM包的命令为`yum update -y packagename`，加`-y`的原因同`yum install`；另有`yum upgrade -y packagename`，作用与`yum update`类似都是更新本地系统里的该RPM包，不同在于`yum update`会先去更新软件支持列表（也称RPM源）。 26 | 27 | ## 安装源码包 28 | 安装源码包有3个主要步骤，分别是`./configure`、`make`、`make install`。 29 | 30 | ### 前置工作 31 | 安装源码包除了上述3个主要步骤，我们还需要前期的一些准备工作： 32 | - 在官方站点下载源码包，并且基于约定俗成，把源码包放到`/usr/local/src`目录。 33 | - 视源码包格式而定，挑选压缩工具进行解压。 34 | 35 | ### ./configure 36 | 这一步骤的主要作用就在于： 37 | - 定制软件安装的功能/配置； 38 | - 检查系统环境以及是否具有编译该源码包所需要的库； 39 | - 生成 Makefile 文件； 40 | 41 | 关于软件可定制的功能/配置，我们可以通过命令`./configure --help`来进行查看，此时实际上并不会真的执行`./configure`，而是显示一个帮助文档。 42 | 43 | 最常用的可配置项莫过于`--prefix`，该配置项的意思是定义软件包的安装路径。 44 | 45 | 在确定好所有配置项后，我们可以执行形如以下的命令：`./configure --prefix=/usr/local/appache2`，此时就开始检测安装环境了，如果有问题，按照提示信息操作（如安装缺失了的库/包）即可。 46 | 47 | 如果执行成功，则可看到已生成了`Makefile`；另外也可以执行`echo $?`来验证操作结果，如果结果是0说明执行成功，否则就没有成功。 48 | 49 | ### make 50 | 生成`Makefile`后，需要进行编译，执行命令`make`，执行后，同样可用`echo $?`来验证操作结果。 51 | 52 | ### make install 53 | 通过`make`成功编译后，我们就可以执行安装了，命令为`make install`，执行后，同样可用`echo $?`来验证操作结果。 54 | 55 | 到此，该源码包便已安装完成了。 -------------------------------------------------------------------------------- /content/monitor.md: -------------------------------------------------------------------------------- 1 | # 第十章：监控CentOS的系统状态 2 | 3 | ## 如何查看系统变量 4 | - 执行`env`可以查看系统的环境变量，如主机的名称、当前用户的SHELL类型、当前用户的家目录、当前系统所使用的语言等。 5 | - 执行`set`可以看到系统当前所有的变量，其中包括了： 6 | - 系统的所有预设变量，这其中既包括了`env`所显示的环境变量，也包含了其它许多预设变量。 7 | - 用户自定义的变量。 8 | 9 | ## 监控系统的状态 10 | ### 使用w命令查看当前系统整体上的负载 11 | 使用`w`命令可以查看当前系统整体上的负载： 12 | ``` 13 | # w 14 | 20:33:11 up 309 days, 10:03, 1 user, load average: 0.00, 0.01, 0.05 15 | USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT 16 | root pts/0 113.102.224.86 20:33 3.00s 0.00s 0.00s w 17 | ``` 18 | 需要关注的是第一行的最后一个部分——**load average**，这里的3个数字分别表示了系统在1分钟/5分钟/15分钟内的平均负载值，值越大说明服务器压力就越大。 19 | 20 | 那么，如何看负载是不是太满了呢？其实这个值是与服务器的物理CPU做对比的，那么只要负载值不超过物理CPU数量即可；如当前服务器有两个CPU，那么就尽量不要让负载值超过2。 21 | 22 | ### 用vmstat命令查看系统具体负载 23 | `vmstat`命令打印的结果共分为6部分：procs、memory、swap、io、system和cpu，其中又有许多的细分字段，这里我们重点关注r、b、si、so、bi、bo、wa字段。 24 | 25 | ``` 26 | # vmstat 1 5 27 | procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- 28 | r b swpd free buff cache si so bi bo in cs us sy id wa st 29 | 0 0 0 707116 15392 177284 0 0 81 5 110 267 0 0 99 1 0 30 | 0 0 0 707100 15392 177284 0 0 0 0 121 274 1 0 99 0 0 31 | 0 0 0 706712 15392 177284 0 0 0 0 107 254 0 1 99 0 0 32 | 0 0 0 706696 15392 177284 0 0 0 40 94 235 0 0 100 0 0 33 | 0 0 0 706712 15392 177284 0 0 0 0 93 231 0 0 100 0 0 34 | ``` 35 | 36 | - r(run)：表示正在运行或等待CPU时间片的进程数，**该数值如果长期大于服务器CPU的个数，则说明CPU资源不够用了**。 37 | - b(block)：表示等待资源(I/O、内存等)的进程数。举个例子，当磁盘读写非常频繁时，写数据就会非常慢，此时CPU运算很快就结束了，但进程需要把计算的结果写入磁盘，这样进程的任务才算完成，因此这个任务只能慢慢等待磁盘了。**该数值如果长时间大于1，则需要查一下具体是缺的哪项资源**。 38 | - si和so：分别表示由交换区写入内存的数据量以及由内存写入交换区的数据量；**一般情况下，si、so的值都为0，如果si、so的值长期不为0，则表示系统内存不足**，需要借用磁盘上的交换区，由于这往往对系统性能影响极大，因此需要考虑是否增加系统内存。 39 | - bi和bo：分别表示从块设备读取数据的量和往块设备写入数据的量；**如果这两个值很高，那么表示磁盘I/O压力很大**。 40 | - wa：表示I/O等待所占用CPU的时间百分比。**wa值越高，说明I/O等待越严重。如果wa值超过20%，说明I/O等待严重。** 41 | 42 | 另外，`vmstat`命令后可带两个数字，第一个数字表示每多少秒打印一次结果，第二个数字表示总共打印多少次结果；如果只有第一个数字，则会不停地打印结果，直到你终止该命令。 43 | 44 | ### 用top命令显示进程所占的系统资源 45 | `top`命令的结果有很多信息，但我们主要用它来监控进程所占的系统资源。top命令的结果每隔3秒变1次，它的特点是把占用系统资源（CPU、内存、磁盘I/O等）最高的进程放到最前面。 46 | ``` 47 | PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 48 | 1 root 20 0 41060 3576 2396 S 0.0 0.4 0:00.89 systemd 49 | 2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd 50 | 3 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0 51 | ``` 52 | 这里面我们主要关注RES（所占内存大小）、%CPU、%MEM（占用内存的百分比）、COMMAND这4个字段。 53 | 54 | 另外，如果需要一次性打印系统资源的使用情况，可以使用`top - bn1`。 55 | 56 | ### 监控网卡流量 57 | 58 | #### 使用sar命令查看网卡流量历史记录 59 | 使用`sar`命令前可能需要先进行安装：`yum install -y sysstat`。 60 | 61 | 使用方法是：`sar -n DEV`，第一次使用时会报错，因为还没有生成相应的数据记录。打印出来的结果里有很多字段，我们关注`rxpck/s`和`rxkB/s`。 62 | - `rxpck/s`表示网卡每秒收取的包的数量，如果数值大于4000则考虑是被攻击了。 63 | - `rxkB/s`表示网卡每秒收取的数据量（单位为KB）。 64 | 65 | #### 使用nload命令监控网卡实时流量 66 | 使用`nload`前需进行安装：`yum install -y epel-release;yum install -y nload`。 67 | 68 | 使用起来也很简单，直接使用`nload`命令则可动态显示当前的网卡流入/流出的流量。 69 | 70 | ### 使用free命令查看内存使用状况 71 | 为了检查内存是否够用，除了`vmstat`外，我们还可以使用更直接有效的`free`命令：`free -h`。 72 | 73 | ``` 74 | # free -h 75 | total used free shared buff/cache available 76 | Mem: 992M 141M 462M 516K 388M 714M 77 | Swap: 1.0G 0B 1.0G 78 | ``` 79 | - total：内存总量，相当于used+free+buff/cache=used+available。 80 | - used：已真正使用的内存量。 81 | - free：剩余（未被分配）的内存量。 82 | - shared：不关注。 83 | - buff/cache：缓解CPU和I/O速度差距所用的内存缓存区，由系统预留出来备用，但如果剩余内存都不够用了，那么这部分也是可以挪用出来供服务来使用的。 84 | - available：可用内存，相当于free+buff/cache。 85 | 86 | ### 使用ps命令查看系统进程 87 | 与`top`命令类似，`ps`命令也是用来查看系统具体进程占用资源的情况；由于`top`命令本身是动态的，而`ps`命令是非动态的（相当于执行命令时的一个快照），因此`ps`命令的功能实际上更接近于`top -bn1`。 88 | 89 | ### 使用netstat命令查看网络情况 90 | `netstat`的功能非常强大，这里举两个实际使用场景：`netstat -lnp`（打印当前系统启动哪些端口）和`netstat -an`（打印网络连接状况）。 91 | 92 | ``` 93 | # netstat -an 94 | Proto Recv-Q Send-Q Local Address Foreign Address State 95 | tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 96 | tcp 0 0 172.18.63.215:36492 140.205.140.205:80 ESTABLISHED 97 | ``` 98 | 99 | ``` 100 | netstat -lnp 101 | Active Internet connections (only servers) 102 | Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name 103 | tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 1604/mysqld 104 | tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 1636/httpd 105 | tcp 0 0 0.0.0.0:21 0.0.0.0:* LISTEN 1639/vsftpd 106 | tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 674/sshd 107 | tcp 0 0 0.0.0.0:443 0.0.0.0:* LISTEN 1636/httpd 108 | ``` 109 | -------------------------------------------------------------------------------- /content/process.md: -------------------------------------------------------------------------------- 1 | # 第三章：CentOS的进程系统 2 | 3 | ## 如何暂停以及恢复当前进程的执行 4 | - 使用`Ctrl+D`暂停当前进程。 5 | - 进程被暂停后，使用`fg`把进程恢复到前台继续执行。 6 | - 进程被暂停后，使用`bg`把进程恢复到后台继续执行。 7 | - 如有多个进程被暂停，则可通过`jobs`命令查看其编号，再通过`fg [被暂停进程编号]`或`bg [被暂停进程编号]`，来恢复执行。 8 | 9 | ## 如何让linux命令在后台执行 10 | - 在命令后加上符号`&`即可让linux命令在后台执行，例如`sellp 30 &`。 11 | - 如该linux命令正在前台运行，可使用`Ctrl+D`暂停后，再使用`bg`把进程恢复到后台继续执行。 12 | 13 | ## 如何让后台正在运行的进程转到前台来 14 | 1. 对于所有运行的程序，我们可以用`jobs –l`指令查看，此时记住想要转到前台运行的进程的编号。 15 | 2. 我们可以用`fg %[number]`指令把一个程序调到前台来运行。 16 | 17 | ## 使用kill命令结束一个进程 18 | `kill`命令的语法是`kill 进程的pid`；有时这样并不能终止进程，可以考虑使用`kill -9 进程的pid`，这会强制终止一个进程。 19 | 20 | 进程的pid可以通过`top`命令或`ps`命令进行查看。 -------------------------------------------------------------------------------- /content/rsync.md: -------------------------------------------------------------------------------- 1 | ## 备份工具rsync 2 | rsync是Linux系统下最具代表性的数据备份工具，它具有以下特点： 3 | - 不仅可以远程同步，还可以在本地进行同步。 4 | - 增量更新，减少同步的流量。 5 | - 可以在windows和mac下使用，能够做到跨平台使用。 6 | - 可以很容易做到保持原来文件的权限、时间、软硬链接等等。 7 | - 比较安全，可以使用scp、ssh等方式来传输文件，当然也可以通过直接的socket连接。 8 | 9 | ### rsync的命令格式 10 | `rsync`命令的格式是：`rsync [OPTION]... SRC DEST`；其中，SRC和DEST既可以取本地目录/文件，也可以取远程目录/文件，如`rsync [OPTION]... SRC [USER@]HOST:DEST`或`rsync [OPTION]... SRC [USER@]HOST::DEST`。 11 | 12 | SRC可以由多个文件组成，以此来实现一次性指定同步多个文件：`rsync [OPTION]... SRC1 SRC2 SRC3 DEST`。 13 | 14 | ### rsync的常用参数 15 | - -a：归档模式，表示以递归方式传输文件，并保持所有属性，它等同于`-rlptgoD`，这是最常用的参数。另外，为灵活起见，`-a`后可跟一个`--no-OPTION`来表示关闭`-rlptgoD`中的任意一个参数，比如`-a--no-l`等同于`-rptgoD`。 16 | - -r：表示以递归模式处理子目录。 17 | - -v：表示打印同步的汇总结果信息。 18 | - -l：表示保留软连接。 19 | - -L：表示如果SRC中含有软连接文件，则取其指向的目标文件同步到DEST（当然软连接就不会同步过去了）。 20 | - --delete：表示删除DST中SRC没有的文件。 21 | - --exclude=PATTERN：表示指定排除不需要传输的文件。 22 | - --progress：表示动态打印rsync同步过程中的状态以及最后的汇总结果信息（即包含了`-V`的效果）。 23 | - -z：表示将会在同步传输过程中压缩。 24 | 25 | ### rsync远程同步 26 | 虽然rsync可以在本地的两个目录中进行同步，但其实rsync更常见的应用场景应该是在两台机器中进行远程同步（不论是通过局域网还是互联网）。 27 | 28 | #### 通过ssh的方式进行远程同步 29 | 其命令格式(注意是只有一个**冒号**)如下： 30 | - `rsync [OPTION]... SRC [USER@]HOST:DEST` 31 | - `rsync [OPTION]... [USER@]HOST:SRC DEST` 32 | 33 | 在输入命令后，接下来的事情其实跟openssh的反馈十分类似：如没有通过密钥认证，则需要输入密码进行认证。认证通过后，接下来的rsync执行结果就跟在本地同步操作的没有两样了。 34 | 35 | #### 通过rsync后台服务(rsyncd)的方式进行远程同步 36 | 这种方式的原理是在远程服务器上建立rsync服务器，并将本机看成是rsync客户端，这样我们就可以利用rsync客户端远程连接(via TCP)rsync服务器进行远程同步的操作了。 37 | 38 | 下面我们分**服务器端**和**客户端**两个部分来解释通过rsync后台服务(rsyncd)的方式进行远程同步的整个过程。 39 | 40 | ##### 服务器端 41 | 42 | ###### rsync配置文件 43 | 启动rsync后台服务rsyncd前，我们需要先准备一份rsyncd的配置文件——`/etc/rsyncd.conf`，该配置可控制rsync的权限、可操作范围、日志、可用模块等方方面面的内容。 44 | 45 | 配置文件由两个部分组成：全局变量和模块变量，但你也可以把模块变量写在全局变量里，作为模块变量的一份默认值。 46 | 47 | 下面列出一些常用的变量，具体的变量列表请查询[官方文档](https://download.samba.org/pub/rsync/rsyncd.conf.html)。 48 | 49 | - 全局变量 50 | - pid file：指定pid文件路径(记录rsyncd的进程ID) 。 51 | - port：指定监听哪个端口，默认是873端口。 52 | - address：指定启动服务的IP，假如你的服务器有多个IP，那么可以指定其中的一个IP来启动rsyncd服务；如果不指定则默认在全部IP上启动 53 | - 模块变量 54 | - path：指定该模块的根目录，客户端在访问该模块时不能超出该根目录的层级范围。另外，此变量可以达成某些骚操作，比如`path=/home/%RSYNC_USER_NAME%`，则当连接服务器端的rsync用户名为**test**时，该模块的根目录就自动设置为`/home/test`，但为了安全起见，不推荐这么干。 55 | - use chroot：值取**true**或**false**，表示在传输文件前，首先`chroot`到**path参数**所指定的目录下，这样做可以获得额外的安全防护；但是缺点是需要以root权限来启动rsyncd，并且，如果同步的内容里有软连接指向模块根目录以外的文件，则不能实现同步。 56 | - max connections：指定该模块最大的连接数，如果有超出此最大连接数的客户端试图连接，则会被告知**try later**；该值默认为0，即没有限制最大连接数。 57 | - log file：指定日志文件的路径，默认使用**syslog**。该日志文件意义非常重大，尤其是在架构rsync服务初期，可能会遇到相当多的问题，需要通过查看日志来定位问题所在。同时，即使为模块设置了**log file**，还是建议给全局设置一份，因为有些权限校验的异常，还是会被记录到全局日志文件里的。 58 | - read only：值取**true**或**false**，决定客户端是否能往服务器端上传/删除文件，默认为**false**。 59 | - write only：值取**true**或**false**，决定客户端是否能从服务器端下载文件。 60 | - list：值取**true**或**false**，决定客户端查询服务器端所有可用模块时是否显示，默认显示。 61 | - uid/gid：决定传输文件时以哪个身份（用户/组）进行传输，这关系到rsyncd是否有相应的文件系统权限来读取或修改文件。如果不设置此参数，则据此逻辑处理：如果rsyncd由超级用户启动，则以**nobody**这个系统用户的身份进行传输；否则，按启动rsyncd的用户身份进行传输。因此，如果想以root/root身份进行传输，则必须设置此参数为`uid=root;gid=root`。 62 | - filter/include from/include/exclude from/exclude：表示同步文件的白名单及黑名单；虽然在rsync客户端使用的`rsync`命令里也有对应的可选参数，但在服务器端设置的话，更具有强制性和隐蔽性（在客户端访问的时候，只会反馈"不存在"，而非"不允许访问"）。 63 | - auth users：表示身份验证的规则，不设置则表示所有rsync用户都可访问。指定对象的方式有两种：1. 指定用户名，此用户名并不一定要真实存在于Linux系统中；2. 指定用户组名（并在用户组名前加上`@`以区分开用户名），这个方式是依托于Linux系统的，因此客户端连接使用的用户名以及此处指定的用户组都必须是真实存在于Linux系统中。多个对象可用空格或逗号进行分隔（推荐使用逗号，因为如果使用空格来分隔，那么在用户名/组名中带有空格的情况下，会造成混淆）。另外可以使用参数`deny`/`ro`(read only)/`rw`(read write)来具体控制某个用户或某个组的访问权限，如：`auth users = , joe:deny, @Some Group:deny, admin:rw, @RO Group:ro`。 64 | - secrets file：指定一个声明`用户名:用户密码`或`@用户组名：用户组公共密码`的文件，该参数是`auth users`参数的配套，仅在已设置`auth users`参数的情况下生效，且没有默认值。另外，即使你在`auth users`参数中指定了用户组作为对象，也不一定要在本文件中声明`@用户组名：用户组公共密码`，完全可以罗列出用户组中所有用户的`用户名:用户密码`来满足需求。 65 | - strict modes：值取**true**或**false**，且默认值为**true**。如取**true**值，则`secrits file`参数所对应的文件，其文件系统权限必须设定为600。 66 | - hosts allow / hosts deny：表示rsync客户端的白名单及黑名单，可根据IP或IP段进行设置，且支持以空格为分隔符输入多个对象。 67 | 68 | 这里给出一份参考的rsyncd配置文件： 69 | ``` 70 | port=873 71 | log file=/var/log/rsync.log 72 | pid file=/var/run/rsyncd.pid 73 | 74 | [test] 75 | path=/root/rsync/test 76 | use chroot=false 77 | max connections=0 # no limitation 78 | read only=false 79 | list=true 80 | uid=root 81 | gid=root 82 | auth users=rsyncuser 83 | secrets file=/etc/rsyncd.passwd 84 | ``` 85 | ###### 启动rsyncd 86 | 启动方式有以下两种： 87 | - 独立的服务：`rsync --daemon --config=/etc/rsyncd.conf`。 88 | - 由**inetd**在监听到请求时再行启动，这里不作阐述。 89 | 90 | ###### rsyncd自启 91 | 为保证rsyncd的可用性（比如在系统异常重启后依然可用），需要把rsyncd设置为开机自启，具体方法请查询`chkconfig`或`systemd`。 92 | 93 | ##### 客户端 94 | 95 | ##### 命令格式 96 | 在这种方式下的命令格式稍有区别：`rsync [OPTION]... RSYNCUSER@HOST::[MODULE[/SRC]] DEST`。多个对象的命令也有所区别：`rsync [OPTION]... RSYNCUSER@HOST::[MODULE1[/SRC1]] ::[MODULE2[/SRC2]] ::[MODULE3[/SRC3]] DEST` 97 | 98 | ##### 关于用户身份验证 99 | 若rsyncd设置了`auth users`，那么客户端在连接的时候就需要提供相应rsync用户的密码了： 100 | - 直接用`rsync [OPTION]... RSYNCUSER@HOST::[MODULE[/SRC]] DEST`命令，接下来会提示需要输入密码。 101 | - 指定存放rsync用户密码的文件路径：`rsync -avL --password-file=/etc/rsyncd.passwd RSYNCUSER@HOST::[MODULE[/SRC]]，此密码文件中，就只放密码： 102 | ``` 103 | # cat /etc/rsyncd.passwd 104 | test123 105 | ``` 106 | 107 | ### rsync进阶运用 108 | 109 | #### rsync配合inotify实现文件目录实时同步 110 | 需求假设是这样的： 111 | - 服务器A随着程序的执行，不断产生新的日志。 112 | - 服务器B和C需要把服务器A上的日志拉取过来，并需要保证实时性。 113 | 114 | 如果我们用crond轮询来启动rsync发起同步，不仅实时性得不到保证，另外也很可能造成资源的浪费。 115 | 116 | 那么，就有了下面这套方案： 117 | - 在服务器B和C上启动rsyncd。 118 | - 在服务器A上利用inotify监控日志的产生，每逢有新日志产生inotify都会调用我们写好的shell脚本，这样我们就可以在脚本中，把服务器A作为rsync客户端，远程连接服务器B和C，达到把服务器A上新产生的日志推送到服务器B和C上的目的。 119 | 120 | -------------------------------------------------------------------------------- /content/shell.md: -------------------------------------------------------------------------------- 1 | # 第七章：shell相关 2 | 3 | ## 区分登录/非登录shell，以及交互式/非交互式shell 4 | ### 登录/非登录shell 5 | - 登录shell(login shell)指的是需要用户输入用户名和密码才能进去的shell，这是比较常用的。 6 | - 非登录shell(non-login shell)则相反，不需要用户输入用户名和密码，例如： 7 | - 直接命令`bash`(不带`--login`参数)就是打开一个新的非登录shell。 8 | - 在图形界面（如Gnome或KDE）中打开一个“终端”(terminal)窗口程序也是属于打开了一个非登录shell。 9 | 10 | ### 交互式/非交互式shell 11 | - 交互式shell(interactive shell)指的是shell等待自然人用户在终端上的输入，并且按照用户输入的命令立即执行且返回执行结果，这种操作模式被称为“交互式模式”，是我们最直观、最常用的操作方式。 12 | - 非交互式shell(non-interactive shell)针对的并非自然人用户，它通常是以 shell script （即以 shell 的语法所写成的程序代码段）的方式执行。 13 | - 运行shell脚本程序时，系统将创建一个子shell。此时，系统中将有两个shell，一个是登录时系统启动的shell，另一个是系统为运行脚本程序创建的shell。 14 | - 当一个脚本程序运行完毕，它的脚本shell将终止，可以返回到执行该脚本之前的shell。 15 | - 从这种意义上来说，用户可以有许多 shell，每个shell都是由某个shell（称为父shell）派生的。 16 | 17 | ### 不同类型shell初始化时所执行的startup脚本不一样 18 | > 对于Bash来说，登录shell（包括交互式登录shell和使用`–-login`选项的非交互shell），它会首先读取和执行`/etc/profile`全局配置文件中的命令，然后依次查找`~/.bash_profile`、`~/.bash_login` 和 `~/.profile`这三个配置文件，读取和执行这三个中的第一个存在且可读的文件中命令。除非被`–noprofile`选项禁止了。另外，由于`~/.bash_profile`一般也会带有执行`~/.bashrc`的代码段，因此`~/.bashrc`的内容也会被执行。 19 | 20 | > 在非登录shell里，只读取 `~/.bashrc` （和 `/etc/bash.bashrc`、`/etc/bashrc` ）文件，不同的发行版里面可能有所不同。 21 | 22 | 从上可得，无论是登录shell还是非登录shell，最终都会执行`~/.bashrc`。 23 | 24 | ## 如何让变量突破shell脚本程序的上下文限制：`export`与`source` 25 | 在子 shell 中定义的变量只在该子 shell 内有效。如果在一个 shell 脚本程序中定义了一个变量，当该脚本程序运行时，这个定义的变量只是该脚本程序内的一个局部变量，其他的 shell 不能引用它。 26 | 27 | 有两种方法可以使子 shell 中的变量突破上下文限制，在其它 shell 中也能使用： 28 | - 在脚本代码中使用`export`语句可以对已定义的变量进行输出，如下： 29 | ``` 30 | a=2333 31 | export a 32 | ``` 33 | `export`命令将使系统在创建每一个新的子 shell 时定义这个变量的一个拷贝。这个过程称之为变量输出。 34 | - 在交互式 shell 中使用`source`命令来执行脚本程序，系统将不会生成新的子 shell 来执行脚本程序，而是直接在当前的交互式 shell 中执行；那么，脚本程序中所有定义（或改变）的变量，都将在当前 shell 中起效。 35 | 36 | 37 | ## 如何配置Linux用户的工作环境，并在下次登录依然保持有效 38 | 当我们直接在命令行里执行配置工作环境的命令，如`alias`，赋值自定义变量等操作时，这些配置仅适用于当前登录的会话，若当前用户退出系统，则这些配置均失效。 39 | 40 | 首先需要明确的是，既然针对的是“Linux用户的工作环境”，那么实际上我们执行的是**登录交互式shell**；因此，若想要这些工作环境的配置在下次登录依然保持有效，可以这样做： 41 | 42 | 43 | - “全局配置”，指的是为当前系统的每一个用户都设置一致的工作环境配置。全局配置的方式是：在`/etc/profile`文件中进行编辑或添加命令语句。 44 | - “每个用户私有配置”，指的是针对Linux中具体某个用户进行特定的工作环境配置，其方式为：在`~/.bash_profile`中进行编辑或添加命令语句。 45 | 46 | ## shell变量规则 47 | - 赋值变量的格式为`a=b`，其中a为变量名，b为赋给变量的值，需要注意的是，等号两边不能有空格。 48 | - 变量名只能由字母、数字以及下划线组成，而且不能以数字开头。 49 | - 当变量内容带有特殊字符（如空格）时，需要加上单引号，如`myname='array huang'`；如果变量内容中本来就含有单引号，此时就需要加双引号了，如`myname="'array huang'"`。 50 | - 如变量中需要用到linux命令的执行结果，可以使用反引号，如 51 | ``` 52 | pwdResult=`pwd` 53 | ``` 54 | - 拼接变量的方法如下：`myname="$firstName"Huang` 55 | 56 | ## `grep`命令和`egrep`命令不一样的地方 57 | `egrep`是`grep`的扩展版本，因此在功能上前者比后者更为强大，下面介绍它们不同的地方： 58 | - `egrep`支持更多的正则表达式用法： 59 | - `?`(表示0个或1个指定的字符)； 60 | - `+`(表示至少1个指定的字符)； 61 | - `|`(逻辑或连接符)，如`'a|b'`，指的是匹配含有 a **或** b 的字符串； 62 | - `()`表示把多个字符合为1个整体来进行表达，通常搭配其它正则表达式符号来使用，如`'r(oo|at)o'`，指的是匹配含有 rooo 或 rato 的字符串； 63 | - 在`{}`的用法上，`grep`的使用比较麻烦，需要加上转义字符`\`，如`'o\{2\}'`(表示匹配含有 oo 的字符串)；而`egrep`的使用则自然得多，同样的正则表达式，直接使用`'o{2}'`即可。 64 | 65 | ## shell脚本 66 | 67 | ### shell脚本的创建和执行 68 | - shell脚本应以`#! /bin/bash`开头来表明该脚本使用的是 bash 语法，如果不写，也能正常运行，但就不符合编码规范了。 69 | - shell脚本的执行有两种方法： 70 | - 执行命令`sh ./file.sh`，并且可以考虑加上`-x`参数，这样就能查看脚本每一步执行的命令与结果了，非常利于调试程序。 71 | - 直接执行`./file.sh`，这种方法使用的前提是用户拥有脚本的执行权限(即**x**权限)，需要注意的是新建脚本文件时一般是没有执行权限的，需要通过`chmod`进行修改。 72 | 73 | 因此一般我们直接用第一种方法即可。 74 | 75 | ### 脚本常用命令及语法 76 | 在 shell 脚本中，命令可看作是一般程序语言中的预设函数。 77 | 78 | #### 时间 79 | `date`，时间格式化和简单的计算（如“一天前”、“一小时后”等）。 80 | - 命令(函数)的结果可以通过反引号来赋值给变量，如 81 | ``` 82 | nowDate=`date +"%Y-%m-%d"` 83 | ``` 84 | 85 | #### 数学运算 86 | - 数学运算有特别的语法： 87 | - 用`$[]`给括起来(只支持整数运算)，如： 88 | ``` 89 | a=1 90 | b=2 91 | c=$[$a+$b+3] 92 | echo $c // 结果是6 93 | ``` 94 | - 95 | - 使用`let`(只支持整数运算)： 96 | 97 | ``` 98 | var=1 99 | let "var+=1" 100 | echo $var 101 | ``` 102 | - 103 | - 使用`(())`(只支持整数运算)： 104 | ``` 105 | var=1 106 | ((var+=1)) 107 | echo $var 108 | ``` 109 | - 110 | - 使用bc(可以进行浮点数计算)： 111 | ``` 112 | var=1 113 | var=`echo "$var+1"|bc` 114 | echo $var 115 | ``` 116 | 其原理是：bc是linux下的一个简单计算器，支持浮点数计算，在命令行下输入bc即进入计算器程序，而我们想在程序中直接进行浮点数计算时，利用一个简单的管道即可解决问题。 117 | 118 | #### 和用户交互 119 | 使用`read`命令可达到与用户交互的目的，它会把用户输入的字符串作为变量值，如： 120 | 121 | ``` 122 | read -p "please input a number:" x # 执行后等待用户输入并按回车确认 123 | echo "$x" 124 | ``` 125 | 126 | #### 执行shell脚本时传参 127 | 在执行脚本时，我们可以通过对脚本传参（当然前提是脚本被设计成可以接受参数），来改变脚本的具体行为，以及得到以此计算出来的结果。 128 | 129 | 脚本内获取参数的格式为：$n。（n代表一个数字，，1 为执行脚本的第一个参数，2 为执行脚本的第二个参数，以此类推……）。 130 | 131 | 举例说明，当前有一个名为**test.sh**的脚本： 132 | 133 | ``` 134 | #!/bin/bash 135 | 136 | echo "Shell 输出脚本名称及参数"; 137 | echo "执行的脚本名：$0"; 138 | echo "第一个参数为：$1"; 139 | echo "第二个参数为：$2"; 140 | echo "第三个参数为：$3"; 141 | ``` 142 | 143 | 运行输出： 144 | 145 | ``` 146 | $ ./test.sh 1 2 3 147 | 148 | Shell 传递参数实例！ 149 | 执行的文件名：./test.sh 150 | 第一个参数为：1 151 | 第二个参数为：2 152 | 第三个参数为：3 153 | ``` 154 | 155 | #### 逻辑判断 156 | 共有以下3种语法： 157 | - 不带`else`： 158 | ``` 159 | if [判断语句]; then 160 | command 161 | fi 162 | ``` 163 | - 带`else`: 164 | ``` 165 | if [判断语句]; then 166 | command 167 | else 168 | command 169 | fi 170 | ``` 171 | - 带`elif`： 172 | ``` 173 | if [判断语句]; then 174 | command 175 | elif [判断语句]; then 176 | command 177 | else 178 | command 179 | fi 180 | ``` 181 | 182 | ##### if语句 183 | ###### 字符串判断 184 | 185 | - str1 = str2　　　　　　当两个串有相同内容、长度时为真 186 | - str1 != str2　　　　　 当串str1和str2不等时为真 187 | - -n str1　　　　　　　 当串的长度大于0时为真(串非空) 188 | - -z str1　　　　　　　 当串的长度为0时为真(空串) 189 | - str1　　　　　　　　 当串str1为非空时为真 190 | 191 | ###### 数字的判断 192 | 193 | - int1 -eq int2　　　　两数相等为真 194 | - int1 -ne int2　　　　两数不等为真 195 | - int1 -gt int2　　　　int1大于int2为真 196 | - int1 -ge int2　　　　int1大于等于int2为真 197 | - int1 -lt int2　　　　int1小于int2为真 198 | - int1 -le int2　　　　int1小于等于int2为真 199 | 200 | ###### 文件的判断 201 | 202 | - -r file　　　　　用户可读为真 203 | - -w file　　　　　用户可写为真 204 | - -x file　　　　　用户可执行为真 205 | - -f file　　　　　文件为正规文件为真 206 | - -d file　　　　　文件为目录为真 207 | - -c file　　　　　文件为字符特殊文件为真 208 | - -b file　　　　　文件为块特殊文件为真 209 | - -s file　　　　　文件大小非0时为真 210 | - -t file　　　　　当文件描述符(默认为1)指定的设备为终端时为真 211 | 212 | ###### 复杂逻辑判断 213 | 214 | - && 　 　　　　　 与 215 | - ||　　　　　　　 或 216 | - !　　　　　　　　非 217 | 218 | 举例： 219 | ``` 220 | a=10 221 | if [$a -lt 1] || [$a -gt 5]; then 222 | echo ok; # 输出ok 223 | fi 224 | ``` 225 | 226 | #### case语句 227 | 语法如下： 228 | ```bash 229 | case 变量 in 230 | value1) 231 | command 232 | ;; 233 | value2) 234 | command 235 | ;; 236 | *) 237 | command 238 | ;; 239 | esac 240 | ``` 241 | 结合执行shell脚本时传入的参数，可以实现功能的切换： 242 | ```bash 243 | #!/bin/bash 244 | case $1 in 245 | start|s) ## |表示or，在这里表示匹配start或s均可 246 | echo service is running 247 | ;; 248 | stop) 249 | echo service is stoped 250 | ;; 251 | reload) 252 | echo service is reload 253 | ;; 254 | *) 255 | echo xxxxx 256 | ;; 257 | esac 258 | ``` 259 | 260 | #### for循环 261 | 语法如下： 262 | ``` 263 | for 变量名 in 循环的条件; do 264 | command 265 | done 266 | ``` 267 | 268 | ##### 循环条件 269 | - 数字递进：`((i=1;i<=10;i++))` 270 | - 列举一组字符串或数字，以空格分隔：`1 2 3 aaa bbb` 271 | - 命令执行的结果： 272 | ```bash 273 | for i in `ls`; do 274 | echo $i is file name\! 275 | done 276 | ``` 277 | - 变量的值： 278 | ```bash 279 | list="rootfs usr data data2" 280 | for i in $list; do 281 | echo $i is appoint 282 | done 283 | ``` 284 | - 执行脚本时传入的参数： 285 | ```bash 286 | #!/bin/bash 287 | 288 | echo "number of arguments is $#" # $#表示参数的个数 289 | 290 | echo "What you input is: " 291 | 292 | for argument in "$@"; do # $@表示参数列表，此处也可以使用$*代替，$*则把所有的参数当作一个字符串 293 | echo "$argument" 294 | done 295 | ``` 296 | 297 | #### while循环 298 | 语法： 299 | ``` 300 | while [循环(判断)的条件]; do 301 | command 302 | done 303 | ``` 304 | 305 | 注意此处的***循环(判断)的条件***与`if`语句中的判断条件是一样的。 306 | 307 | #### 函数 308 | ##### 函数定义语法： 309 | ```bash 310 | function 函数名() { 311 | command 312 | [return] # 可return也可不return 313 | } 314 | ``` 315 | 316 | ##### 函数的调用方法是： 317 | ```bash 318 | #!/bin/bash 319 | function show() { 320 | echo "hello , you are calling the function" 321 | } 322 | echo "first time call the function" 323 | show 324 | echo "second time call the function" 325 | show 326 | ``` 327 | 328 | ##### 如函数需要传入参数，则使用$1、$2……等取用： 329 | ```bash 330 | #!/bin/bash 331 | function show() { 332 | echo "hello , you are calling the function $1" 333 | } 334 | echo "first time call the function" 335 | show first # 输出hello , you are calling the function first 336 | echo "second time call the function" 337 | show second # 输出hello , you are calling the function second 338 | ``` 339 | 340 | ##### 函数中的关键字“return”可以放到函数体的任意位置，通常用于返回某些值，Shell在执行到return之后，就停止往下执行，返回到主程序的调用行，return的返回值只能是0~256之间的一个整数，返回值将保存到变量“$?”中。 341 | ``` 342 | #!/bin/bash 343 | function test() { 344 | return 0 345 | } 346 | 347 | test 348 | echo "$?" # 输出0 349 | ``` 350 | 351 | ##### 如果函数在另外一个文件中，我们该怎么调用它呢？ 352 | 我们可以使用`source`命令，比如 show 函数写在了function.sh里面了： 353 | ```bash 354 | source function.sh 355 | show 356 | ``` 357 | 358 | ##### 函数的变量作用域 359 | 默认情况下，变量具有全局作用域，如果想把它设置为局部作用域，可以在其前加入local 360 | 361 | 例如： 362 | ```bash 363 | local a=hello 364 | ``` 365 | 使用局部变量，使得函数在执行完毕后，自动释放变量所占用的内存空间，从而减少系统资源的消耗，在运行大型的程序时，定义和使用局部变量尤为重要。 366 | 367 | ##### 函数的嵌套 368 | 函数可以进行嵌套，实例： 369 | ```bash 370 | #!/bin/bash 371 | function first() { 372 | function second() { 373 | function third() { 374 | echo "------this is third" 375 | } 376 | echo "this is the second" 377 | third 378 | } 379 | echo "this is the first" 380 | second 381 | } 382 | 383 | echo "start..." 384 | first 385 | ``` 386 | 387 | #### shell脚本中的中断和继续 388 | 389 | ##### break 390 | 与其它程序语言一样，`break`是用来跳出当前的循环的，`break`后可加数字，如`break 2`表示跳出两层的循环。 391 | 392 | ##### continue 393 | 与其它程序语言一样。 394 | 395 | ##### exit 396 | 退出脚本，或者更准确地说，是退出当前运行脚本的shell（既然运行环境关闭了，那么脚本当然也不能继续执行下去了）。 397 | 398 | 在函数中使用`exit`，是会退出整个脚本的，因此若只是想退出函数，请使用`return`。 399 | 400 | `exit`后可接数字作为状态码，如`exit 0`；一般来说，**0**表示脚本执行成功，其它状态码则表示各种可能的异常情况 401 | 402 | ## 别名 403 | 我们可以通过`alias`命令把一个常用的并且很长的指令另取名为一个简单易记的指令；如果不想用了，还可以使用`unalias`来取消。 404 | 405 | - 使用`alias`命令，可以列出系统当前所有的别名。 406 | - 使用`alias [命令别名]=['具体的命令']`可以自定义别名，例如：`alias aming='pwd'`。 407 | - 使用`unalias`可以取消别名，例如`unalias aming`。 408 | 409 | ## 重定向 410 | 重定向分为“输入重定向”和“输出重定向”，重定向一般通过在命令间插入特定的符号来实现。 411 | 412 | - `command1 > file1`，这个命令执行command1然后将执行后输出的内容存入file1。注意任何file1内的已经存在的内容将被新内容替代。如果要将新内容添加在文件末尾，请使用>>操作符。 413 | - `command1 < file1`，执行command1，使用file1作为用来替代键盘的输入源。 414 | - `command1 < infile > outfile`，同时替换输入和输出，执行command1，从文件infile读取内容，然后将输出写入到outfile中。 415 | 416 | 另外，上述的“输出内容”仅指命令执行的结果，若命令执行中出现错误，则错误信息需要另行处理： 417 | 418 | - `command1 2> file1`，执行command1，然后将标准错误输出重定向到文件file1。 419 | - 另外一个很有用的功能是将标准错误输出融合到标准输出中去，这样错误信息可以和其他普通的输出信息一起处理。例如：`command > file 2>&1`，这表示将command执行后的结果与错误信息均写入到file里。 420 | 421 | ## 管道符 422 | 管道符的标识为`|`，它用于将前一个指令的输出作为后一个指令的输入，格式如下：`command1 | command2`，举例说明：`yum list | grep zip | head -n 5`。 -------------------------------------------------------------------------------- /content/ssh.md: -------------------------------------------------------------------------------- 1 | ## SSH远程登录 2 | Linux系统通过sshd(ssh daemon)服务实现远程登录的功能，其默认端口是22，此服务为Linux系统预装，并预设开机自启，因此不需要额外设置便能够实现Linux远程登录。 3 | 4 | ### Linux系统上的ssh客户端——openssh 5 | Windosw系统上有许多软件可以实现ssh远程登录，比如说putty、SecureCRT、Xshell等，那么，我们在Linux系统上，应该使用哪个ssh客户端呢？这里推荐使用**openssh-clients**(简称**openssh**)。 6 | 7 | ### ssh的校验登录方式 8 | ssh支持两种方法进行远程校验登录：使用密码登录和使用密钥登录。 9 | 10 | #### 使用密码登录 11 | 使用命令`ssh user@host`，如`ssh root@192.168.80.128`，系统会进一步提示输入密码，正确输入后，你已经成功登录到远程服务器上了，你的一切操作都跟本地操作无异。 12 | 13 | #### 使用密钥认证登录 14 | 由于密码登录存在易泄露、易破解的问题，因此一般主张使用ssh远程登录时，仅使用密钥进行登录，并关闭密码远程登录的权限。 15 | 16 | 所谓密钥认证，实际上是使用了一对加密的字符串：公钥(public key)和私钥(private key)，其一般使用**RSA**算法生成。公钥用于加密，任何人都可以看到其内容；而私钥用于解密，只有拥有者才能看到其内容；那么显而易见，即使坏人拿到公钥，也无法解读加密后的内容，因此可以保证内容的保密性。 17 | 18 | 下面介绍具体的操作： 19 | 1. 为本地本用户账号生成一个密钥对：`ssh-keygen`，系统会进一步提示你输入密钥存放的目标目录，按回车键保持默认即可（默认为`~/.ssh`）；接下来会提示你输入密钥的密码，一般留空即可（直接按回车键）；此时会告知你密钥对已成功生成。 20 | 2. 查看刚生成的公钥内容：`cat ~/.ssh/id_rsa.pub`。 21 | 3. 方法有两个： 22 | - 使用命令`ssh-copy-id user@host`即可把本地的公钥复制到远程服务器的**authorized_keys**文件上，并给相应的目录和文件设置好合适的权限，详情请看这里[SSH-COPY-ID](https://www.ssh.com/ssh/copy-id)。 23 | - 复制公钥的全部内容，粘贴到远程服务器的`~/.ssh/authorized_keys`里。远程服务器上如果不存在这个**authorized_keys**文件，则直接新建一个；如果已存在，则注意需要另起一行，加到此文件末尾。这一个过程也可使用以下命令进行操作：`$ ssh user@host 'mkdir -p .ssh && cat >> .ssh/authorized_keys' < ~/.ssh/id_rsa.pub`。需要注意，使用此手动方法，需要相应的设置好**authorized_keys**文件的权限，推荐为**600**。 24 | 4. 大功告成，从此你使用ssh远程登录，就不需要再输入密码了。 25 | 26 | ### 使用ssh远程执行命令并获得执行结果 27 | 28 | #### 例子1：复制公钥 29 | 上述的`$ ssh user@host 'mkdir -p .ssh && cat >> .ssh/authorized_keys' < ~/.ssh/id_rsa.pub`就是一个很好的例子： 30 | 1. `ssh user@host`，表示登录远程主机； 31 | 2. 单引号中的`mkdir .ssh && cat >> .ssh/authorized_keys`，表示登录后在远程shell上执行的命令； 32 | 3. `mkdir -p .ssh`的作用是：如果用户主目录中的.ssh目录不存在，就创建一个； 33 | 4. `cat >> .ssh/authorized_keys' < ~/.ssh/id_rsa.pub`的作用是：将本地的公钥文件`~/.ssh/id_rsa.pub`，重定向追加到远程文件**authorized_keys**的末尾。 34 | 35 | #### 例子2：查看远程主机是否运行进程httpd 36 | ``` 37 | $ ssh user@host 'ps ax | grep [h]ttpd' 38 | ``` 39 | 40 | ### 退出当前ssh会话 41 | 使用`exit`命令或`logout`命令即可。 -------------------------------------------------------------------------------- /content/system-log.md: -------------------------------------------------------------------------------- 1 | ## Linux系统日志 2 | 3 | ### 核心系统日志文件——/var/log/messages 4 | Linux的核心系统日志文件是`/var/log/messages`，它包含了以下内容： 5 | - 系统启动时的引导消息 6 | - I/O错误 7 | - 网络错误 8 | - 其它系统运行时发送的错误 9 | - 单纯的操作记录 10 | 11 | `/var/log/messages`是由**rsyslogd**这个守护进程生成的，如果**rsyslogd**被停止了，则系统将不会生成新的`/var/log/messages`。 12 | 13 | ### 安全日志 14 | 15 | #### 使用`last`命令查看Linux系统的登录日志 16 | ``` 17 | # last | head 18 | root pts/0 192.168.80.1 Mon Feb 5 11:28 still logged in 19 | root tty1 Mon Feb 5 11:26 still logged in 20 | reboot system boot 3.10.0-693.11.1. Mon Feb 5 11:26 - 11:28 (00:01) 21 | root tty1 Sun Feb 4 11:34 - crash (23:51) 22 | ``` 23 | 上面的字段从左到右依次为账户名称、登录终端、登录客户端IP、登录时间段。 24 | 25 | 以上面这4条截取的日志来分析，它们是按时间从新到旧进行排列的，因此我们先从第四条开始分析。第四条日志其实是我在虚拟机以root账户登录后直接关闭虚拟机，因此我们可以发现，账户名称是root，登录终端是tty1（相当于本地登录了），没有客户端IP（因为是本地登录），登录时间段的末尾是**crash**（因为我不是正常的关机）。 26 | 27 | 根据上面的逻辑继续来分析就非常清晰了： 28 | - 第3条是我重新开机虚拟机的日志； 29 | - 第2条是开机成功后，我在本地使用root账户登录； 30 | - 第1条是我在本物理机(windows系统)，开SecureCRT，同样使用root账户，进行远程登录（虽然两个系统在同一台物理机上，但虚拟机是相对独立的，因此其实看作这是两台机器，所以也就是远程登录而非本地登录了）。 31 | 32 | 另外再介绍一个与登录信息有关的日志文件——`/var/log/secure`： 33 | ``` 34 | Feb 5 11:28:14 localhost sshd[1462]: pam_unix(sshd:session): session opened for user root by (uid=0) 35 | Feb 5 11:28:14 localhost sshd[1462]: Accepted password for root from 192.168.80.1 port 53703 ssh2 36 | Feb 5 11:26:46 localhost login: ROOT LOGIN ON tty1 37 | Feb 5 11:26:46 localhost login: pam_unix(login:session): session opened for user root by LOGIN(uid=0) 38 | Feb 5 11:26:37 localhost sshd[1102]: Server listening on :: port 22. 39 | Feb 5 11:26:37 localhost sshd[1102]: Server listening on 0.0.0.0 port 22. 40 | Feb 5 11:26:35 localhost polkitd[535]: Acquired the name org.freedesktop.PolicyKit1 on the system bus 41 | Feb 5 11:26:35 localhost polkitd[535]: Finished loading, compiling and executing 2 rules 42 | Feb 5 11:26:35 localhost polkitd[535]: Loading rules from directory /usr/share/polkit-1/rules.d 43 | Feb 5 11:26:35 localhost polkitd[535]: Loading rules from directory /etc/polkit-1/rules.d 44 | Feb 4 21:36:42 localhost sshd[1434]: pam_unix(sshd:session): session closed for user root 45 | ``` 46 | 对照着`last`命令的结果，`/var/log/secure`是不是挺容易看明白的呢？ -------------------------------------------------------------------------------- /content/systemd.md: -------------------------------------------------------------------------------- 1 | # 第一章：CentOS的系统服务管理系统 2 | 3 | ## Linux系统服务管理 4 | 从CentOS7开始，CentOS的服务管理工具由SysV改为了systemd，但即使是在CentOS7里，也依然可以使用`chkconfig`这个原本出现在SysV里的命令。 5 | 6 | Systemd的设计目标是，为系统的启动和管理提供一套完整的解决方案。 7 | 8 | ### chkconfig服务管理工具 9 | 10 | #### 罗列chkconfig所管理的服务 11 | 使用`chkconfig --list`命令可以列出所有的服务及其在每个级别(run level)下的自启状态。 12 | ``` 13 | netconsole 0:off 1:off 2:off 3:off 4:off 5:off 6:off 14 | network 0:off 1:off 2:on 3:on 4:on 5:on 6:off 15 | ``` 16 | 这里我们只关心第3级和第5级：第3级表示完整的多用户模式，是标准的运行级，也即我们平常最常用的文字模式；第5级表示图形界面的管理模式。 17 | 18 | 需要注意的是，在CentOS7中，`chkconfig`只保留极少量的SysV服务，其它服务请使用systemd进行管理。 19 | 20 | #### 使用chkconfig更改某服务在某级别下的自启状态 21 | 例如，使用`chkconfig --level 345 network off`即可关闭network这个服务在第3/4/5级中的自启；另外如果不传入参数`--level`，则默认针对级别2/3/4/5操作。 22 | 23 | #### 为chkconfig添加/删除管理的服务项 24 | 简单例如： 25 | ``` 26 | # chkconfig --del network 27 | # chkconfig --add network 28 | ``` 29 | 30 | ### systemd服务管理工具 31 | 32 | #### 罗列systemd所管理的服务 33 | 使用`systemctl list-units --all --type=service`： 34 | ``` 35 | # systemctl list-units --all --type=service 36 | UNIT LOAD ACTIVE SUB DESCRIPTION 37 | aegis.service loaded active running LSB: aegis update. 38 | agentwatch.service loaded active exited SYSV: Starts and stops guest agent 39 | aliyun-util.service loaded active exited Initial Aliyun Jobs 40 | aliyun.service loaded active running Aliyun Service Daemon 41 | ``` 42 | 43 | 这些服务对应的启动脚本文件保存在`/usr/lib/systemd/system`。 44 | 45 | #### systemd的基本概念 46 | systemd把系统的各项资源（包括各个服务、设备等）都看作是**unit**，unit有许多种类，我们目前关心的是**service**和**target**。这里的service并不是什么新概念，因此只解释一下target：target是多个unit的组合，启动一个target也就相当于启动其中包含的所有unit；SysV中的run level在systemd里被target所取代，例如系统以多用户文字模式(runlevel 3)启动时，就会启动**multi-user.target**，而以图形界面模式(runlevel 5)启动时，则会启动**graphical.target**；target之间并非互斥的，因此可以同时启动多个target。 47 | 48 | 我们可以用`systemctl list-dependencies multi-user.target`来列举multi-user.target所包含的内容： 49 | ``` 50 | # systemctl list-dependencies multi-user.target 51 | multi-user.target 52 | ● ├─aegis.service 53 | ● ├─agentwatch.service 54 | ● ├─aliyun-util.service 55 | ● ├─aliyun.service 56 | ● ├─brandbot.path 57 | ● ├─crond.service 58 | ● ├─dbus.service 59 | ● ├─network.service 60 | ● ├─ntpd.service 61 | ● ├─plymouth-quit-wait.service 62 | ● ├─plymouth-quit.service 63 | ● ├─rc-local.service 64 | ● ├─rsyslog.service 65 | ● ├─sshd.service 66 | ● ├─sysstat.service 67 | ● ├─systemd-ask-password-wall.path 68 | ● ├─systemd-logind.service 69 | ● ├─systemd-readahead-collect.service 70 | ● ├─systemd-readahead-replay.service 71 | ● ├─systemd-update-utmp-runlevel.service 72 | ● ├─systemd-user-sessions.service 73 | ● ├─basic.target 74 | ● │ ├─microcode.service 75 | ● │ ├─rhel-autorelabel-mark.service 76 | ● │ ├─rhel-autorelabel.service 77 | ● │ ├─rhel-configure.service 78 | ● │ ├─rhel-dmesg.service 79 | ● │ ├─rhel-loadmodules.service 80 | ● │ ├─paths.target 81 | ● │ ├─slices.target 82 | ● │ │ ├─-.slice 83 | ● │ │ └─system.slice 84 | ● │ ├─sockets.target 85 | ● │ │ ├─dbus.socket 86 | ● │ │ ├─systemd-initctl.socket 87 | ● │ │ ├─systemd-journald.socket 88 | ● │ │ ├─systemd-shutdownd.socket 89 | ● │ │ ├─systemd-udevd-control.socket 90 | ● │ │ └─systemd-udevd-kernel.socket 91 | ● │ ├─sysinit.target 92 | ● │ │ ├─dev-hugepages.mount 93 | ● │ │ ├─dev-mqueue.mount 94 | ● │ │ ├─kmod-static-nodes.service 95 | ● │ │ ├─ldconfig.service 96 | ● │ │ ├─plymouth-read-write.service 97 | ● │ │ ├─plymouth-start.service 98 | ``` 99 | 100 | 可以看出这其中就包含了不少target，比如**basic.target**，因此target是可以嵌套的。 101 | 102 | #### systemd常用命令 103 | ``` 104 | # systemctl enable crond.service // 让某个服务开机自启(.service可以省略) 105 | # systemctl disable crond // 不让开机自启 106 | # systemctl status crond // 查看服务状态 107 | # systemctl start crond // 启动某个服务 108 | # systemctl stop crond // 停止某个服务 109 | # systemctl restart crond //重启某个服务 110 | # systemctl reload * # 重新加载服务配置文件 111 | # systemctl is-enabled crond // 查询服务是否开机启动 112 | ``` 113 | 114 | ## systemd功能介绍 115 | Systemd 是 Linux 的系统工具，用来启动守护进程，已成为大多数发行版的标准配置。 116 | 117 | 它的设计目标是，为系统的启动和管理提供一套完整的解决方案。 118 | 根据 Linux 惯例，字母d是守护进程（daemon）的缩写。 Systemd 这个名字的含义，就是它要守护整个系统。 119 | 120 | 从CentOS7开始，CentOS的服务管理工具由SysV改为了systemd，但即使是在CentOS7里，也依然可以使用`chkconfig`这个原本出现在SysV里的命令。 -------------------------------------------------------------------------------- /content/vim.md: -------------------------------------------------------------------------------- 1 | # Vim的使用 2 | 3 | ## vim基本操作 4 | 5 | ### 移动光标 6 | 下面操作均需处在一般模式（默认的模式）下： 7 | - `h``j``k``l`分别为“左”“下”“上”“右” 8 | - 翻半页：`Ctrl + d`(`d` for down)，`Ctrl + u`(`u` for up)。 9 | - 翻一页：`Ctrl + f`(`f` for front)，`Ctrl + b`(`b` for back)。 10 | - `gg`表示移到到首行。 11 | - `G`表示移动到尾行。 12 | - `nG`(`n`指的是数字)表示移动到第n行；一般用于根据程序错误提示信息进行 bug fix。 13 | - `0`表示移到光标所在行的行首； $表示移动到光标所在行的行尾。 14 | 15 | ### 复制剪切粘贴 16 | 17 | - 按`yy`复制光标所在行。 18 | - 按`dd`剪切光标所在行，如果光剪切不粘贴，那就相当于删除。 19 | - 按`p`将复制/剪切的内容粘贴至光标后，因为光标是在具体字符的位置上，所以实际是在该字符的后面；整行的复制粘贴在游标的下一行。 20 | 21 | #### v模式相关 22 | - 按`v`切换到“高亮选择模式”，移动光标进行选择。 23 | - 在`v模式`下，按`y`(`y` for yank)复制高亮选择的内容。 24 | - 在`v模式`下，按`d`剪切高亮选择的内容，如果光剪切不粘贴，那就相当于删除。 25 | 26 | ### 撤销、重做 27 | 以下仅讨论vim下的操作（vi的操作稍有不同）： 28 | - 按`u`进行撤销，可多次撤销。 29 | - 按`Ctrl + r`(`r` for redo)进行重做，可多次重做。 30 | 31 | ### 进入编辑模式 32 | 下面所有操作均需在一般模式下执行： 33 | - `i`，在当前光标所在字符前插入。 34 | - `o`，在当前光标所在行的下一行插入新的一行。 35 | - `O`，在当前光标所在行的上一行插入新的一行。 36 | 37 | ### 查找和替换字符串 38 | 下面所有操作均需在一般模式下执行： 39 | - `/word`，向下查找一个字符串word，查找后按`n`看下一匹配结果，按`N`看上一匹配结果。 40 | - `?word`，向上查找一个字符串word，查找后按`n`看下一匹配结果，按`N`看上一匹配结果。 41 | - `:n1,n2s/word1/word2/g`，在n1和n2行之间查找word1并替换为word2，其中n1、n2皆可取数字，另外n2可取$表示最后一行。 42 | 43 | ### 行号相关 44 | - `:set nu`表示显示行号。 45 | - `:set nonu`表示不显示行号。 46 | 47 | ### 保存及退出 48 | - `:w`，保存文本。 49 | - `:q`，退出vim。 50 | - `:w!`，强制保存，在root用户下，即使文本只读也可以完成保存。 51 | - `:q!`，强制退出，所有改动不生效。 52 | - `:wq`，保存并退出。 -------------------------------------------------------------------------------- /content/xargs.md: -------------------------------------------------------------------------------- 1 | # 神奇的xargs命令 2 | 3 | ## xargs命令：将stdin转换成传入其它命令的参数 4 | `xargs`命令的作用在于给别的命令传递参数，其一般配合管道符`|`来使用，把前一命令的stdout作为自己的stdin，再转换成`command line`形式的参数传给其它命令。 5 | 6 | ### xargs命令的语法 7 | 其一般出现的形式如下： 8 | ``` 9 | OtherCommand [options] | xargs [options] [TargetCommand [options]] 10 | ``` 11 | 如： 12 | ``` 13 | find /tmp -name "*.log" -type f -print | xargs /bin/rm -f 14 | ``` 15 | 上面这是`xargs`命令的常用场景，配合`find`命令，找到`/tmp`目录下所有日志文件并予以删除。 16 | 17 | ### xargs命令的意义 18 | - 虽然管道能把别的命令的stdout作为下个命令的stdin传入，但毕竟并非所有的命令都接受stdin的，如`ls`；比较常见接受stdin的命令有`cat`、`less`；而`xargs`命令能转化stdin的命令正好弥补了这些不接受stdin的命令的不足。 19 | - 对于大数据量的操作来说，如上面的例子，一次性删除大量文件，若直接使用`rm -f /tmp/*.log`，很可能会报错`/bin/rm Argument list too long`，而如果我们用上`xargs`命令，`xargs`会帮我们把待删的文件分批交给`rm`命令来执行。 20 | - 某些命令针对`xargs`调用的方式进行了优化，达到更进一步的效果，如： 21 | ```bash 22 | # ls | xargs ls 23 | file1 file2 file3 24 | 25 | dir1: 26 | file4 27 | 28 | dir2: 29 | file5 file6 file7 30 | ``` 31 | 32 | ### xargs命令的工作原理 33 | 想了解`xargs`命令的工作原理，其实很简单；`xargs`命令在不指定目标命令时，其默认目标命令实际上是`echo`： 34 | ``` 35 | # ls ./ | xargs echo 36 | file1 file2 file3 37 | # ls ./ | xargs 38 | file1 file2 file3 39 | # ls ./ 40 | file1 file2 file3 41 | ``` 42 | 从以上命令的执行结果我们可以看到，`xargs`命令实际上就是**将所有空格、制表符和分行符都替换为空格并压缩到一行上显示，这一整行将作为一个字符串传入到目标命令中**。 43 | 44 | 以下两个命令实际上是等价的： 45 | ```bash 46 | # ls ./ | xargs echo 47 | file1 file2 file3 48 | # echo 'file1 file2 file3' 49 | file1 file2 file3 50 | ``` 51 | 52 | 明白了`xargs`命令的工作原理，那么其实它所支持的options也很好理解，实际上就是如何将stdin传来的结果转化成不同的字符串，如处理分隔符的问题、转化成多个字符串分批执行的问题。 53 | --------------------------------------------------------------------------------