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SEC-L07-001.1利用口令猜测与网络窃听进行口令破解2010年4月实验课件摘要技术背景：口令破解，做为黑客常用的攻击手段之一，在攻击阶段实现了口令的暴力猜测、信息窃取。
精心构造的口令字典、口令强度较低的账户、性能强劲的运算系统，能够快速、有效地完成口令破解。
口令破解技术主要分为3类：本地破解、在线破解、口令窃听。
这些做为简单、常用、直接的黑客攻击手段，我们很有必要了解这种技术！实验目的：口令破解、窃听口令、口令字典实验平台攻击机(客户端)：Windows2000/XP/2003、Linux被攻击机(服务端)：Linux Server实验工具：NmapL0phtCrack、John the RipperBrutus、Hydra、Spcrk流光、X-Scan、超级字典生成器.、黑客字典IITcpdump、Wireshark、Cain实验要点：●黑客字典生成技术；●本地口令文件暴力破解；●远程服务在线口令暴力破解；●网络传输明文口令信息窃听；实验步骤指导：生成暴力字典推荐工具：超级字典生成器1.说明：使用字典生成工具可以快速生成复杂的单词、数字、特殊符号组成的字典，攻击者可以根据条件生成想要的各种字典，从而提高暴力猜测的速度。
2.运行“超级字典生成器”，程序界面如下图：3.根据个人需求，选择相关选项生成字典；字典生成要求：生成以a-z小写字母组成，长度为3位，3位字母不重复的账户字典，文件保存为user.txt；请生成4位0-9数字组成的密码字典，文件保存为pass.txt；本地口令文件暴力破解推荐工具：L0phtCrack、John the Ripper说明：在某些时候，攻击者窃取了操作系统的账户信息文件，如Windows下的SAM文件、Linux下的shadow文件。
攻击者可以在本地实现暴力猜测。
Windows2000/XP/2003客户端环境1.运行“L0phtCrack”程序；【知识重点】※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※L0phtCrack黑客工具的一种。
SEC-L05-001.1Linux漏洞利用2010年4月Linux 漏洞利用技术背景Linux 操作系统是一款开源的类UNIX操作系统，有多种发行版（Distributions），如RedHat Linux、SUSE Linux、Debian Linux等等等等。
这些发行版在系统安装、包管理、桌面应用等方面各有特色，但是其操作系统内核（Kernel）均来自于一个组织（），该组织负责Linux内核的更新、发布。
在部分已发布的内核版本中，存在一些严重影响操作系统安全的漏洞，Hacker 或Cracker通过利用这些漏洞达到入侵并控制目标主机的目的，Cracker 甚至会通过这些漏洞入侵有问题的主机及该主机所在网络，以达到窃取保密信息、散播蠕虫木马、发起DDOS攻击等目的。
实验目的通过2种不同漏洞的利用（内核调用漏洞及系统工具漏洞），对普通帐号进行本地提权，通过实际操作增加实验者对网络安全及主机操作系统安全的认识，对希望成为合格的SA（System Administrator & Security Administrator）的实验者进行系统漏洞类的部分基础知识介绍。
实验平台攻击机(客户端)：Windows2000/XP/2003目标机(服务端)：Linux Server实验工具Putty（putty.exe）及Putty SFTP 工具（psftp.exe）SSH口令在线扫描工具X-Scan演示后门程序ndoor实验要点远程SSH服务在线口令暴力破解Linux本地提权简易后门制作实验步骤指导实验准备实验概要：熟悉了解相关的实验工具，掌握Putty，Putty SFTP，X-Scan等工具的使用，操作。
1、下载实验中使用的工具：Putty（putty.exe）及Putty SFTP 工具（psftp.exe）、SSH口令在线扫描工具X-Scan 、演示后门程序ndoor※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※【知识重点】putty.exe 是一个小巧实用的远程登录客户端，支持多种协议。
linux安全策略与实例
在Linux操作系统中，安全性是非常重要的一个环节。
以下是一些建议的Linux安全策略，以及对应的实例。
安全策略一：最小权限原则
最小权限原则是指只授予用户和应用程序执行其任务所需的最小权限。
这可以减少潜在的安全风险，例如权限提升或数据泄露。
实例：在设置Linux文件权限时，只给予文件所有者读写权限，而不是给予整个用户组或其他人读写执行权限。
安全策略二：防火墙配置
防火墙是保护Linux系统免受未经授权访问的第一道防线。
通过配置防火墙规则，可以限制对系统的网络访问。
实例：使用iptables配置防火墙规则，只允许特定的IP地址或IP地址范围访问特定的端口。
安全策略三：使用强密码
强密码是防止未经授权访问的关键。
强密码应该包含大小写字母、数字和特殊字符，并且长度至少为8个字符。
实例：设置密码"AbcD@123"，它包含了大写字母、小写字母、数字和特殊字符，长度为8个字符。
安全策略四：及时更新系统
及时更新系统可以防止已知的漏洞被利用。
Linux发行版通常会定期发布安全更新。
实例：使用apt-get或yum命令定期更新系统，并安装所有安全更新。
安全策略五：使用加密技术保护数据
加密技术可以保护数据在传输和存储过程中的安全性。
使用加密技术可以防止数据被窃取或篡改。
实例：使用SSH协议进行远程登录，使用加密技术保护数据传输；使用LUKS 加密技术对硬盘进行加密，保护数据存储安全。
Ruijie#conf tEnter configuration commands, one per line. End with CNTL/Z.Ruijie(config)#int g0/1 ----进入需要配置System Guard功能的接口Ruijie(config-if-GigabitEthernet 0/1)#system-guard enable---开启System Guard功能Ruijie(config-if-GigabitEthernet 0/1)#system-guard isolate-time 600----配置非法用户的隔离时间。
取值范围为30 秒到3600 秒，缺省值为120 秒Ruijie(config-if-GigabitEthernet 0/1)# system-guard same-dest-ip-attack-packets 100----配置对某个不存在的IP 不断的发IP 报文进行攻击的最大阈值Ruijie(config-if-GigabitEthernet 0/1)# system-guard scan-dest-ip-attack-packets 100----配置对一批IP 网段进行扫描攻击的最大阈值Ruijie(config-if-GigabitEthernet 0/1)#exit ----退出到全局模式Ruijie(config)#system-guard detect-maxnum 200 ----设置监控主机的最大数Ruijie(config)#system-guard exception-ip 192.168.1.1/24----添加防攻击功能的特例IP地址Ruijie(config)#exit ----退出到特权模式Ruijie#clear system-guard ----清除所有已被隔离用户Ruijie#clear system-guard interface g0/1 ----清除该端口下被隔离的所有用户Ruijie#clear system-guard interface g0/1 192.168.1.1---清除该接口下被隔离的指定IP用户注意：设置设备监控攻击主机的最大数。
第35卷 第4期 福 建 电 脑 Vol. 35 No.42019年4月Journal of Fujian ComputerApr. 2019———————————————本文得到福建省教育厅中青年教师教育科研项目基金 (No. JAT170720)资助。
张志阳(通信作者)，男，1985年生，主要研究领域为电子信息安全、计算机网络。
E-mail: 280781305@ 。
吴秀丽，女，1986年生，主要研究领域为电子信息。
E-mail: 632541395@ 。
金承勇，男，1978年生，主要研究领域为电子信息。
E-mail: 453793002@ 。
Linux 环境中网络边界安全防御系统设计与实现张志阳 吴秀丽 金承勇(仰恩大学工程技术学院 福建 泉州 362000)摘 要 本文基于Linux 系统，结合多种开源的软件平台搭建应用于企业网络安全防御的系统。
通过应用领域、技术选择、应用实施和系统整体架构等思路，设计企业级网络边界及网络安全防御系统，为企业网络的安全提供了可靠的平台保障。
关键词 Linux ；防火墙；VPN ；入侵检测；主动防御 中图法分类号 TP393 DOI:10.16707/ki.fjpc.2019.04.004Design and Implementation of a Border Security Defense System Based onLinux NetworkZHANG Zhiyang, WU Xiuli, JIN Chengyong(College of Engineering and Technology, Yang-En University, Quanzhou, China, 362000)Abstract This paper builds a system for enterprise network security defense based on Linux system combined with a variety of open source software platforms. Through the application field, technology selection, application implementation and overall system architecture, the enterprise-level network boundary and network security defense system are designed to provide a reliable platform guarantee for enterprise network security. Keywords Linux; Firewall; VPN; Intrusion Detection; Active Defense1 引言目前，基于Linux 开源系统的日渐盛行，在大中型企业及微小型企业的应用已经得到普及。
Linux终端命令之系统安全和防火墙配置Linux系统是一种开源的操作系统，广泛应用于各种服务器和个人计算机上。
然而，在网络环境中，系统安全和防火墙配置是至关重要的。
本文将介绍Linux终端命令中与系统安全相关的常用命令，以及如何配置和管理防火墙来保护系统免受恶意攻击。
一、系统安全命令1. 更改密码在Linux系统中，我们可以使用passwd命令来更改当前用户的密码。
在终端中输入命令"passwd"后，系统会提示输入当前密码和新密码。
请注意，为了安全起见，密码应该是复杂的，包含大小写字母、数字和特殊字符。
2. 用户管理为了保护系统免受未经授权的访问，我们需要定期查看和管理用户账户。
常用的命令有：- 添加用户：可以使用useradd命令添加新用户，例如"sudo useradd username"，其中"username"是新用户的名称。
- 删除用户：使用userdel命令删除指定的用户账户，例如"sudo userdel username"。
- 修改用户属性：使用usermod命令修改用户的属性，例如"sudo usermod -g groupname username"，其中"groupname"是新的用户组名称。
3. 文件权限文件权限是保护系统中文件和目录安全的重要因素。
通过使用chmod命令，我们可以改变文件和目录的权限。
例如，"sudo chmod 600 filename"将文件的权限设置为只允许拥有者读写。
4. SSH访问设置SSH（Secure Shell）是远程登录Linux系统的一种安全方式。
为了提高系统安全性，建议修改SSH配置文件/etc/ssh/sshd_config，禁用root用户远程登录，并启用公钥身份验证。
修改后，需要重启SSH服务。
安恒网站卫士网页防篡改系统操作手册目录1产品简介······················································································································ 1-1 2登录防篡改管理系统······································································································· 2-12.2 注销 ························································································································2-22.3 主题 ························································································································2-32.3.1 黑色风格主题····································································································2-32.3.2 Metro风格 ·······································································································2-32.4 关于 ························································································································2-4 3监控频道······················································································································ 3-43.1 组查询······················································································································3-53.2 监控端查询················································································································3-5 4监控端管理··················································································································· 4-64.1 组管理······················································································································4-64.1.2 添加················································································································4-64.1.3 查询················································································································4-64.1.4 删除················································································································4-74.1.5 查看编辑··········································································································4-74.2 监控端管理················································································································4-84.2.2 立即激活··········································································································4-84.2.3 取消激活··········································································································4-94.2.4 查询················································································································4-94.2.5 删除·············································································································· 4-114.2.6 批量分组········································································································ 4-114.2.7 绑定模板········································································································ 4-114.2.8 解除模板········································································································ 4-124.2.9 查看编辑········································································································ 4-134.2.10 监控端配置 ··································································································· 4-134.2.11 发布端配置 ··································································································· 4-224.3 模板配置管理··········································································································· 4-254.3.1 添加·············································································································· 4-254.3.2 查询·············································································································· 4-264.3.3 删除·············································································································· 4-274.3.4 编辑查看········································································································ 4-27i / 78安恒网站卫士网页防篡改系统操作手册4.3.5 绑定模板········································································································ 4-274.3.6 模板配置········································································································ 4-28 5发布端管理··················································································································5-355.1 发布端管理·············································································································· 5-355.1.1 查询·············································································································· 5-355.1.2 删除·············································································································· 5-365.1.3 编辑查看········································································································ 5-365.1.4 发布端配置····································································································· 5-375.2 发布日志················································································································· 6-385.2.1 查询·············································································································· 6-385.2.2 删除·············································································································· 6-395.2.3 快速查询········································································································ 6-39 6日志···························································································································6-386.1 篡改日志················································································································· 6-386.1.1 查询·············································································································· 6-406.1.2 删除·············································································································· 6-406.1.3 快速查询········································································································ 6-416.1.4 导出·············································································································· 6-416.2 攻击日志················································································································· 6-416.2.1 查询·············································································································· 6-426.2.2 删除·············································································································· 6-426.2.3 快速查询········································································································ 6-426.2.4 导出·············································································································· 6-436.3 事件日志················································································································· 6-436.3.1 查询·············································································································· 6-436.3.2 删除·············································································································· 6-446.3.3 快速查询········································································································ 6-446.3.4 导出·············································································································· 6-44 7报表···························································································································7-457.1 报表 ······················································································································ 7-457.1.1 篡改日志报表·································································································· 7-457.1.2 攻击日志报表·································································································· 7-49 8系统管理·····················································································································8-538.1 服务器状态·············································································································· 8-538.2 用户信息················································································································· 8-548.2.1 修改admin帐号 ······························································································ 8-54ii / 78。
配置Linu系统进行主动防御2021年4月实验课件摘要技术背景系统平安始终是信息网络平安的一个重要方面，攻击者往往通过控制操作系统来破坏系统和信息，或扩大已有的破坏。
对操作系统进行平安加固就可以减少攻击者的攻击时机实验目的了解系统加固可以采取的手段：1.了解Linu系统帐户创立，密码设置，登录管理；加强对Linu系统的访问控制了解〔i mand=<指令>执行完指定的指令后即恢复原来的身份。
-f或--fast 适用于csh与tsch，使shell不用去读取启动文件。
或--login 改变身份时，也同时变更工作目录，以及HOME,SHELL,USER,LOGNAME。
此外，也会变更,-ent 变更身份时，不要变更环境变量。
-s<shell>或--shell=<shell> 指定要执行的shell。
--hel itRootLogin no复原为#itRootLogin yes重起SSH效劳命令：# service sshd restart使用-auth命令：$ vi /etc/system-auth在system-auth文件的auth局部增加如下一行〔红字的局部〕auth required /lib/security/$ISA/auth required /lib/security/ onerr=fail no_magic_rootauth sufficient /lib/security/$ISA/ lieauth nulloauth required /lib/security/$ISA/1.在system-auth文件的account局部增加如下一行〔红字的局部〕，然后保存并关闭system-auth文件account required /lib/security/$ISA/account required /lib/security/ deny=3 no_magic_root resetaccount sufficient /lib/security/$ISA/ uid < 100 quietaccount required /lib/security/$ISA/2.设定含义为：尝试密码出现错误超过3次，那么锁定帐号3.保存并关闭system-auth文件。
如何在Linux终端中进行系统监控和报警Linux终端是系统管理员和开发人员的重要工具，它不仅提供了快速和高效的操作方式，还允许用户通过系统监控和报警来实时追踪系统的运行状态。
在本文中，将介绍如何在Linux终端中进行系统监控和报警的方法。
1. 使用top命令进行系统监控top命令是Linux系统中最常用的系统监控命令之一，它可以实时显示系统的运行状态、进程等相关信息。
在终端中输入top命令后，会显示类似下面的信息：top - 09:15:27 up 30 days, 15:06, 2 users, load average: 0.08, 0.04, 0.01 Tasks: 170 total, 1 running, 169 sleeping, 0 stopped, 0 zombie%Cpu(s): 0.1 us, 0.1 sy, 0.0 ni, 99.8 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 stMiB Mem : 15867.6 total, 5566.1 free, 4757.6 used, 5544.0buff/cacheMiB Swap: 1024.0 total, 1024.0 free, 0.0 used. 10662.0 avail MemPID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND433 root 20 0 323052 109816 2876 S 0.0 0.7 0:00.16 Xorg 434 root 20 0 88544 54208 8272 S 0.0 0.3 0:00.69 lightdm ...在top命令的输出中，可以看到系统的运行时间、负载均衡、进程状态、CPU和内存使用情况等。
通过定期执行top命令，可以实时监控系统的性能指标，并及时做出相应的调整。
2. 使用sar命令进行系统性能监控sar命令是System Activity Reporter的缩写，它可以收集并报告系统的运行状态、性能指标等。
银河麒麟操作系统涉密专用版初始口令介绍银河麒麟操作系统涉密专用版是一种为涉密环境而设计的高安全性操作系统。
为确保系统的安全性，在初次安装系统时，用户需要设置初始口令。
本文将详细介绍银河麒麟操作系统涉密专用版初始口令的相关内容，包括设置初始口令的目的和重要性，初始口令的要求和最佳实践，以及如何保护初始口令的安全。
目的和重要性设置初始口令的目的是为了保护银河麒麟操作系统涉密专用版的安全性。
初始口令是用户登录系统时必须提供的密码，它起到了限制系统访问权限的作用。
一个安全强大的初始口令可以防止未经授权的用户进入系统，避免系统被黑客攻击或者机密数据泄露。
初始口令的要求和最佳实践为了提高系统的安全性，初始口令需要满足以下要求和最佳实践：1. 复杂性初始口令应该是足够复杂，包括字母、数字和特殊字符的组合。
强密码可以增加破解的难度，提高系统的安全性。
2. 长度初始口令的长度应该足够长，一般建议不少于10个字符。
较长的密码可以增加破解的时间成本，降低被猜测到的概率。
3. 不易猜测初始口令应该避免使用容易被猜测到的信息，如个人姓名、生日等。
猜测到的口令容易被攻击者破解，系统的安全性将受到威胁。
4. 定期更改为了保持系统的安全性，初始口令应该定期更改。
建议每隔一定时间（如三个月）更换口令，避免长期使用同一口令导致的安全隐患。
5. 不使用默认口令系统默认口令的安全性较低，容易被攻击者猜测到。
用户在安装系统后应立即更改初始口令，避免使用默认口令。
初始口令的保护初始口令的安全性不仅取决于其复杂度和遵循的最佳实践，还取决于其保护措施。
以下是保护初始口令的一些措施：1. 不共享初始口令是登录系统的凭证，用户不应将其共享给他人。
共享口令会增加系统被攻击的风险，降低系统的安全性。
2. 定期更改如前所述，定期更改初始口令是保持系统安全性的重要措施之一。
定期更改可以减少口令被攻击者猜测到的概率。
3. 密码保险箱对于初始口令以及其他重要密码，用户可以使用密码保险箱进行安全管理。
SEC-L01-001.1配置Linux系统进行主动防御2010年4月实验课件摘要技术背景系统安全始终是信息网络安全的一个重要方面，攻击者往往通过控制操作系统来破坏系统和信息，或扩大已有的破坏。
对操作系统进行安全加固就可以减少攻击者的攻击机会实验目的了解系统加固可以采取的手段：1.了解Linux系统帐户创建，密码设置，登录管理；2.加强对Linux系统的访问控制了解（iptables）；3.熟悉，修改Linux帐号的不安全配置；4.禁止不必要的网络服务。
实验平台客户机(客户端)：Windows2000/XP/2003目标加固主机(服务端)：CentOS 4.6实验工具Putty.exe 工具实验要点Linux系统帐号创建，帐号密码设置；Linux系统帐户登录配置；Linux系统安全访问控制、策略调整（iptables介绍）；实验步骤指导Linux系统帐号创建说明：下载实验中使用的远程连接工具（Putty）并连接目标加固主机添加试验用临时系统帐号。
1.下载Putty.exe，【知识重点】※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※Putty是一个小而精悍的linux服务器远程控制工具，Linux 自带有ssh 服务，开启ssh服务后就可以使用putty远程控制，在使用putty登入时要记得选中SSH，否则是无法远程登入的。
※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※2.点击运行Putty，在出现的窗口界面的hostname处输入实验目标主机ip，并选择ssh，点击“open”。
注：本次实验中远程登录方式采用的都是SSH方式，下面将不再特别说明3.如果出现如下“PuTTY Security Alert”窗口，点击“是”or“Yes”5.将出现如下界面，此时已经使用root帐号登录目标主机成功6.输入如下操作添加试验用系统帐号test（密码也定为test，由于密码强度不够，系统会有所提示，先忽略）命令：[root@LT-courseware-0009 ~]# useradd test[root@LT-courseware-0009 ~]# passwd testChanging password for user test.New UNIX password:（注：此处输入口令）BAD PASSWORD: it is too shortRetype new UNIX password: （注：此处再次输入）passwd: all authentication tokens updated successfully.7.用添加的test帐号按照步骤2）开始的操作方式ssh登录目标主机，如果操作正确将会得到如下界面，显示test已经登录成功8.本部分实验结束，关闭所有实验打开的程序及窗口。
【知识重点】※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※学生通过实验操作了解Linux系统中使用指令进行帐户增加、删除以及帐户密码设置，了解一种Linux系统下帐户添加方式。
※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※useradd功能说明：建立用户帐号。
语法：useradd [-mMnr][-c <备注>][-d <登入目录>][-e <有效期限>][-f <缓冲天数>][-g <群组>][-G <群组>][-s <shell>][-u <uid>][用户帐号] 或 useradd -D [-b][-e <有效期限>][-f <缓冲天数>][-g <群组>][-G <群组>][-s <shell>]补充说明：useradd可用来建立用户帐号。
帐号建好之后，再用passwd设定帐号的密码．而可用userdel删除帐号。
使用useradd指令所建立的帐号，实际上是保存在/etc/passwd文本文件中。
参数：-c<备注> 加上备注文字。
备注文字会保存在passwd的备注栏位中。
-d<登入目录> 指定用户登入时的启始目录。
-D 变更预设值．-e<有效期限> 指定帐号的有效期限。
-f<缓冲天数> 指定在密码过期后多少天即关闭该帐号。
-g<群组> 指定用户所属的群组。
-G<群组> 指定用户所属的附加群组。
-m 自动建立用户的登入目录。
-M 不要自动建立用户的登入目录。
-n 取消建立以用户名称为名的群组．-r 建立系统帐号。
-s<shell>指定用户登入后所使用的shell。
-u<uid> 指定用户ID。
usermod功能说明：修改用户帐号。
语法：usermod [-LU][-c <备注>][-d <登入目录>][-e <有效期限>][-f <缓冲天数>][-g <群组>][-G <群组>][-l <帐号名称>][-s <shell>][-u <uid>][用户帐号]补充说明：usermod可用来修改用户帐号的各项设定。
参数：-c<备注> 修改用户帐号的备注文字。
-d登入目录> 修改用户登入时的目录。
-e<有效期限> 修改帐号的有效期限。
-f<缓冲天数> 修改在密码过期后多少天即关闭该帐号。
-g<群组> 修改用户所属的群组。
-G<群组> 修改用户所属的附加群组。
-l<帐号名称> 修改用户帐号名称。
-L 锁定用户密码，使密码无效。
-s<shell> 修改用户登入后所使用的shell。
-u<uid> 修改用户ID。
-U 解除密码锁定。
userdel功能说明：删除用户帐号。
语法：userdel [-r][用户帐号]补充说明：userdel可删除用户帐号与相关的文件。
若不加参数，则仅删除用户帐号，而不删除相关文件。
参数：-f 删除用户登入目录以及目录中所有文件。
passwd(password)功能说明：设置密码。
语法：passwd [-dklS][-u <-f>][用户名称]补充说明：passwd指令让用户可以更改自己的密码，而系统管理者则能用它管理系统用户的密码。
只有管理者可以指定用户名称，一般用户只能变更自己的密码。
参数：-d 删除密码。
本参数仅有系统管理者才能使用。
-f 强制执行。
-k 设置只有在密码过期失效后，方能更新。
-l 锁住密码。
-s 列出密码的相关信息。
本参数仅有系统管理者才能使用。
-u 解开已上锁的帐号。
※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※禁止root帐号远程登录说明：禁止root帐号远程登录，这对于保证计算机系统的安全，具有实际意义。
9.使用Putty工具以root帐号方式登录到实验目标主机；【知识重点】※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※学生通过实验操作了解Linux系统中的文件内容编辑；※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※Vi进入vi在系统提示字符(如$、#)下敲入vi ＜档案名称＞，vi 可以自动帮你载入所要编辑的文件或是开启一个新文件（如果该文件不存在或缺少文件名）。
进入 vi 后萤幕左方会出现波浪符号，凡是列首有该符号就代表此列目前是空的。
两种模式指令模式和输入模式。
在指令模式下输入的按键将做为指令来处理：如输入a，vi即认为是在当前位置插入字符。
而在输入模式下，vi则把输入的按键当作插入的字符来处理。
指令模式切换到输入模式只需键入相应的输入命令即可（如a,A），而要从输入模式切换到指令模式，则需在输入模式下键入ESC键，如果不晓得现在是处於什麽模式，可以多按几次 [ESC]，系统如发出哔哔声就表示已处于指令模式下了。
付：有指令模式进入输入模式的指令：新增 (append)a ：从光标所在位置後面开始新增资料，光标後的资料随新增资料向後移动。
A：从光标所在列最後面的地方开始新增资料。
插入 (insert)i：从光标所在位置前面开始插入资料，光标後的资料随新增资料向後移动。
I ：从光标所在列的第一个非空白字元前面开始插入资料。
开始 (open)o ：在光标所在列下新增一列并进入输入模式。
O: 在光标所在列上方新增一列并进入输入模式。
退出vi在指令模式下键入:q，:q!，:wq或:x(注意:号），就会退出vi。
其中:wq和:x是存盘退出，而:q是直接退出，如果文件已有新的变化，vi会提示你保存文件而:q 命令也会失效，这时你可以用:w命令保存文件后再用:q退出，或用:wq或:x命令退出，如果你不想保存改变后的文件，你就需要用:q!命令，这个命令将不保存文件而直接退出vi。
基本编辑配合一般键盘上的功能键，像是方向键、[Insert] 、[Delete] 等等，现在你应该已经可以利用 vi 来编辑文件了。
当然 vi 还提供其他许许多多功能让文字的处理更为方便。
何谓编辑？一般认为是文字的新增、修改以及删除，甚至包括文字区块的搬移、复制等等。
先这里介绍 vi 的如何做删除与修改。
（注意：在 vi 的原始观念里，输入跟编辑是两码子事。
编辑是在指令模式下操作的，先利用指令移动光标来定位要进行编辑的地方，然後才下指令做编辑）。
删除与修改文件的命令：x：删除光标所在字符。
dd ：删除光标所在的列。
r ：修改光标所在字元，r 後接著要修正的字符。
R：进入取替换状态，新增文字会覆盖原先文字，直到按 [ESC] 回到指令模式下为止。
s：删除光标所在字元，并进入输入模式。
S：删除光标所在的列，并进入输入模式。
※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※修改/etc/ssh/sshd_config命令：[root@LT-courseware-0009 ~]# vi /etc/ssh/sshd_config查找到#PermitRootLogin yes这一行，作如下修改将注释符“#”号去掉修改“yes”为“no”最终修改该行为：PermitRootLogin no，保存并关闭sshd_config重起SSH服务命令：[root@LT-courseware-0009 ~]# service sshd restart【知识重点】※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※了解Linux系统中通过命令重新启动服务，可以扩展到其他服务重新启动，常用服务启停参数还有start（启动），stop（停止）；※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※使用Putty工具以root帐号方式登录到实验目标主机会发现系统显示Access denied说明root帐号已经无法登录运行一个Putty工具，使用前面创建的test帐号登录到实验目标主机使用su命令，并按照提示输入root密码，转换到root用户身份命令：[test@LT-courseware-0009 ~]$ su -Password:（注：此处输入root密码）[root@LT-courseware-0009 ~]#【知识重点】※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※学生通过实验操作了解Linux系统中的用户身份转换；※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※su(super user)功能说明：变更用户身份。
