Linux SysAdmin DeCal

来自 UCB 的一门讲解 Linux 的入门课程，比起定位相同的 MIT 的公开课 Missing Semester，Decal 讲解得更加系统、也更加清晰，这也是我推荐它的主要原因。比起 Missing Semester 更像是给已经开始编程但没有系统使用过这些工具的学生的查缺补漏，DeCal 更像是面向零基础的同学的课程。一共十二周的课程内容，包括 Linux 基础、shell 编程（还有 tmux 、vim）、包管理、服务(Services)、基础计算机网络、网络服务、安全(密钥管理)、Git、Docker、Kubernetes、Puppet 和 CUDA。十分适合新手了解和入门 Linux 环境相关内容。

美中不足的是部分课程作业需要在远程服务器操作，比如关于 ssh 的练习，需要 UCB 内部账号访问。但是大部分作业可以通过自己搭建的虚拟机 + 使用 Xshell 等工具或者直接使用 Linux 桌面版来操作练习，在听完完整课程和做完作业后，相信已经对 Linux 有最基本的了解了。

为弥补无法使用远程服务器的不足以及熟悉 linux 命令行的需求，在此推荐 bandit 。bandit 是一款来自 OverTheWire 网站的 Wargame，为 CTF 爱好者提供免费的练习靶场。bandit 的前 15 个 level 都是基础的 linux 操作而不涉及任何 CTF 知识。这些练习也正好弥补了 DeCal 外校无法访问的部分（主要是远程链接、文件权限）等内容。

Bandit

Level 0

The goal of this level is for you to log into the game using SSH. The host to which you need to connect is bandit.labs.overthewire.org, on port 2220. The username is bandit0 and the password is bandit0. Once logged in, go to the Level 1 page to find out how to beat Level 1.【此级别的目标是让您使用 SSH 登录游戏。您需要连接的主机是 bandit.labs.overthewire.org，在端口 2220 上。用户名是 bandit0，密码是 bandit0。登录后，转到 Level 1 页面以了解如何通过 Level 1。】

ssh bandit0@bandit.labs.overthewire.org -p 2220

Level 0 → Level 1

The password for the next level is stored in a file called readme located in the home directory. Use this password to log into bandit1 using SSH. Whenever you find a password for a level, use SSH (on port 2220) to log into that level and continue the game.【下一级的密码存储在名为 自述文件位于 HOME 目录中。使用此密码通过 SSH 登录 bandit1。每当您找到某个关卡的密码时，请使用 SSH（在端口 2220 上）登录该关卡并继续游戏。】

通过题目描述我们知道readme文件在桌面上直接 list

ls

出现readme文件，直接读取

cat readme

Congratulations on your first steps into the bandit game!! Please make sure you have read the rules at https://overthewire.org/rules/ If you are following a course, workshop, walkthrough or other educational activity, please inform the instructor about the rules as well and encourage them to contribute to the OverTheWire community so we can keep these games free!

The password you are looking for is: ZjLjTmM6FvvyRnrb2rfNWOZOTa6ip5If

timed out waiting for input: auto-logout Connection to bandit.labs.overthewire.org closed.

【恭喜您迈出了强盗游戏的第一步！请确保您已阅读 https://overthewire.org/rules/ 上的规则。如果您正在参加课程、研讨会、演练或其他教育活动、也请告知讲师相关规则，并鼓励他们并鼓励他们为 OverTheWire 社区做出贡献，这样我们才能保持这些游戏的免费性！您正在寻找的密码是 ZjLjTmM6FvvyRnrb2rfNWOZOTa6ip5If

等待输入超时：自动注销与 bandit.labs.overthewire.org 的连接已关闭。】

Level 1 → Level 2

The password for the next level is stored in a file called - located in the home directory【下一级的密码存储在名为 - 位于主目录中】

./-，这样可以避免 file 命令把 - 误解为选项标志。

cat ./-

263JGJPfgU6LtdEvgfWU1XP5yac29mFx

Level 2 → Level 3

The password for the next level is stored in a file called spaces in this filename located in the home directory【下一级的密码存储在主目录中名为 spaces 的文件中】

ls

文件名叫spaces in this filename

cat 'spaces in this filename'

MNk8KNH3Usiio41PRUEoDFPqfxLPlSmx

Level 3 → Level 4

The password for the next level is stored in a hidden file in the inhere directory.【下一级的密码存储在 inhere 目录中。】

ls

发现inhere目录

cd inhere

进入inhere后 list 发现没有文件显示

ls -A  #-A， --几乎全部，请勿列出隐含的 .和。。

发现...Hiding-From-You文件

cat ...Hiding-From-You

2WmrDFRmJIq3IPxneAaMGhap0pFhF3NJ

Level 4 → Level 5

The password for the next level is stored in the only human-readable file in the inhere directory. Tip: if your terminal is messed up, try the “reset” command.【下一级的密码存储在 inhere 目录中唯一可读的文件中。提示：如果您的终端搞砸了，请尝试 “reset” 命令。】

直接进入inhere目录，list 输出-file00 -file01 -file02 -file03 -file04 -file05 -file06 -file07 -file08 -file09

file ./*  #查看所有文件的类型

./-file00: data ./-file01: data ./-file02: data ./-file03: data ./-file04: data ./-file05: data ./-file06: data ./-file07: ASCII text ./-file08: data ./-file09: data

可以发现只有-file07可以 cat

cat ./-file07

4oQYVPkxZOOEOO5pTW81FB8j8lxXGUQw

Level 5 → Level 6

The password for the next level is stored in a file somewhere under the inhere directory and has all of the following properties:【下一级的密码存储在 inhere 目录下某个位置的文件中，并具有以下所有属性：】

human-readable【人类可读】
1033 bytes in size【大小为 1033 字节】
not executable【不可执行】

这关我的思路是du ./*/* -b查看所有文件的大小

1039 ./maybehere00/-file1 9388 ./maybehere00/-file2 7378 ./maybehere00/-file3 6118 ./maybehere00/spaces file1 6850 ./maybehere00/spaces file2 1915 ./maybehere00/spaces file3 6028 ./maybehere01/-file1 288 ./maybehere01/-file2 9641 ./maybehere01/-file3 4139 ./maybehere01/spaces file1 4543 ./maybehere01/spaces file2 8834 ./maybehere01/spaces file3 3801 ./maybehere02/-file1 3511 ./maybehere02/-file2 4932 ./maybehere02/-file3 6746 ./maybehere02/spaces file1 8488 ./maybehere02/spaces file2 2275 ./maybehere02/spaces file3 315 ./maybehere03/-file1 6595 ./maybehere03/-file2 8275 ./maybehere03/-file3 2190 ./maybehere03/spaces file1 3385 ./maybehere03/spaces file2 9234 ./maybehere03/spaces file3 4410 ./maybehere04/-file1 2619 ./maybehere04/-file2 2117 ./maybehere04/-file3 5532 ./maybehere04/spaces file1 2491 ./maybehere04/spaces file2 6002 ./maybehere04/spaces file3 2346 ./maybehere05/-file1 5959 ./maybehere05/-file2 2572 ./maybehere05/-file3 880 ./maybehere05/spaces file1 2420 ./maybehere05/spaces file2 8585 ./maybehere05/spaces file3 5731 ./maybehere06/-file1 1076 ./maybehere06/-file2 3443 ./maybehere06/-file3 4073 ./maybehere06/spaces file1 4251 ./maybehere06/spaces file2 8065 ./maybehere06/spaces file3 3663 ./maybehere07/-file1 2488 ./maybehere07/-file2 3362 ./maybehere07/-file3 4130 ./maybehere07/spaces file1 9064 ./maybehere07/spaces file2 1022 ./maybehere07/spaces file3 1077 ./maybehere08/-file1 3825 ./maybehere08/-file2 2650 ./maybehere08/-file3 215 ./maybehere08/spaces file1 3693 ./maybehere08/spaces file2 9138 ./maybehere08/spaces file3 3628 ./maybehere09/-file1 774 ./maybehere09/-file2 7961 ./maybehere09/-file3 5301 ./maybehere09/spaces file1 8716 ./maybehere09/spaces file2 7569 ./maybehere09/spaces file3 1052 ./maybehere10/-file1 1991 ./maybehere10/-file2 1237 ./maybehere10/-file3 8269 ./maybehere10/spaces file1 3570 ./maybehere10/spaces file2 2155 ./maybehere10/spaces file3 1211 ./maybehere11/-file1 4559 ./maybehere11/-file2 8854 ./maybehere11/-file3 3147 ./maybehere11/spaces file1 503 ./maybehere11/spaces file2 8845 ./maybehere11/spaces file3 9678 ./maybehere12/-file1 251 ./maybehere12/-file2 9076 ./maybehere12/-file3 2157 ./maybehere12/spaces file1 2460 ./maybehere12/spaces file2 1639 ./maybehere12/spaces file3 1359 ./maybehere13/-file1 1423 ./maybehere13/-file2 3014 ./maybehere13/-file3 3952 ./maybehere13/spaces file1 952 ./maybehere13/spaces file2 4389 ./maybehere13/spaces file3 4282 ./maybehere14/-file1 8351 ./maybehere14/-file2 3756 ./maybehere14/-file3 1382 ./maybehere14/spaces file1 871 ./maybehere14/spaces file2 376 ./maybehere14/spaces file3 8794 ./maybehere15/-file1 9499 ./maybehere15/-file2 6299 ./maybehere15/-file3 1623 ./maybehere15/spaces file1 51 ./maybehere15/spaces file2 1637 ./maybehere15/spaces file3 4277 ./maybehere16/-file1 5301 ./maybehere16/-file2 8085 ./maybehere16/-file3 9773 ./maybehere16/spaces file1 3146 ./maybehere16/spaces file2 7509 ./maybehere16/spaces file3 1133 ./maybehere17/-file1 1791 ./maybehere17/-file2 4422 ./maybehere17/-file3 8361 ./maybehere17/spaces file1 3387 ./maybehere17/spaces file2 6381 ./maybehere17/spaces file3 9697 ./maybehere18/-file1 77 ./maybehere18/-file2 2306 ./maybehere18/-file3 7334 ./maybehere18/spaces file1 6348 ./maybehere18/spaces file2 7040 ./maybehere18/spaces file3 6302 ./maybehere19/-file1 5594 ./maybehere19/-file2 7965 ./maybehere19/-file3 7186 ./maybehere19/spaces file1 8785 ./maybehere19/spaces file2 2307 ./maybehere19/spaces file3

发现并没有字节大小为 1033 的，为什么呢？

* 通配符会匹配文件名中没有点号（.）开头的文件。例如，ls * 会列出所有文件和文件夹，但不会显示隐藏文件（即以 . 开头的文件），这是因为 * 默认不匹配以 . 开头的文件。

如果你想包括以 . 开头的隐藏文件，可以使用 .\*。例如，ls .* 会列出当前目录下所有隐藏文件和目录。

如果你想同时匹配普通文件和隐藏文件，可以使用 .* 和 * 一起：ls * .*。

find . -type f -size 1033c -not -executable -exec file {} + | grep ASCII #.：仅搜索当前工作目录;-type f:仅搜索当前工作目录;-size 1033c 查找大小正好为 1033 字节的文件（Find 使用“c”表示字节）;-not -executable 仅查找非可执行文件

find命令输出./maybehere07/.file2: ASCII text, with very long lines (1000)

-exec file {} +对 find 返回的所有结果执行 file 命令

注意： {} 是一个占位符，表示 find 找到的文件的名称将被替换的位置。“+”号用来批量将多个匹配的文件传递给 file 命令

cat ./maybehere07/.file2

HWasnPhtq9AVKe0dmk45nxy20cvUa6EG

Level 6 → Level 7

The password for the next level is stored somewhere on the server and has all of the following properties:【下一级的密码存储在服务器上的某个位置，并具有以下所有属性：】

owned by user bandit7【归用户 Bandit7 所有】
owned by group bandit6【归 Group Bandit6 所有】
33 bytes in size【大小为 33 字节】

find / -type f -user bandit7 -group bandit6 -size 33c  #/：搜索整个服务器（/ 是 Linux 上的根目录，类似于 Windows 上的 C：/ Drive）;-type: f 仅搜索文件;-user bandit7:搜索用户bandit7拥有的文件;-group bandit6:搜索属于bandit6组的文件;-size 33c:查找大小正好为33字节的文件

find: ‘/drifter/drifter14_src/axTLS’: Permission denied find: ‘/root’: Permission denied find: ‘/snap’: Permission denied find: ‘/tmp’: Permission denied find: ‘/proc/tty/driver’: Permission denied find: ‘/proc/3024060/task/3024060/fdinfo/6’: No such file or directory find: ‘/proc/3024060/fdinfo/5’: No such file or directory find: ‘/home/bandit31-git’: Permission denied find: ‘/home/ubuntu’: Permission denied find: ‘/home/bandit5/inhere’: Permission denied find: ‘/home/bandit30-git’: Permission denied find: ‘/home/drifter8/chroot’: Permission denied find: ‘/home/drifter6/data’: Permission denied find: ‘/home/bandit29-git’: Permission denied find: ‘/home/bandit28-git’: Permission denied find: ‘/home/bandit27-git’: Permission denied find: ‘/lost+found’: Permission denied find: ‘/etc/polkit-1/rules.d’: Permission denied find: ‘/etc/multipath’: Permission denied find: ‘/etc/stunnel’: Permission denied find: ‘/etc/xinetd.d’: Permission denied find: ‘/etc/credstore.encrypted’: Permission denied find: ‘/etc/ssl/private’: Permission denied find: ‘/etc/sudoers.d’: Permission denied find: ‘/etc/credstore’: Permission denied find: ‘/dev/shm’: Permission denied find: ‘/dev/mqueue’: Permission denied find: ‘/var/log/amazon’: Permission denied find: ‘/var/log/unattended-upgrades’: Permission denied find: ‘/var/log/chrony’: Permission denied find: ‘/var/log/private’: Permission denied find: ‘/var/tmp’: Permission denied find: ‘/var/spool/cron/crontabs’: Permission denied find: ‘/var/spool/bandit24’: Permission denied find: ‘/var/spool/rsyslog’: Permission denied find: ‘/var/cache/ldconfig’: Permission denied find: ‘/var/cache/apt/archives/partial’: Permission denied find: ‘/var/cache/pollinate’: Permission denied find: ‘/var/cache/private’: Permission denied find: ‘/var/cache/apparmor/2425d902.0’: Permission denied find: ‘/var/cache/apparmor/baad73a1.0’: Permission denied find: ‘/var/lib/polkit-1’: Permission denied find: ‘/var/lib/amazon’: Permission denied /var/lib/dpkg/info/bandit7.password find: ‘/var/lib/apt/lists/partial’: Permission denied find: ‘/var/lib/chrony’: Permission denied find: ‘/var/lib/snapd/void’: Permission denied find: ‘/var/lib/snapd/cookie’: Permission denied find: ‘/var/lib/private’: Permission denied find: ‘/var/lib/ubuntu-advantage/apt-esm/var/lib/apt/lists/partial’: Permission denied find: ‘/var/lib/update-notifier/package-data-downloads/partial’: Permission denied find: ‘/var/lib/udisks2’: Permission denied find: ‘/var/crash’: Permission denied find: ‘/boot/efi’: Permission denied find: ‘/boot/lost+found’: Permission denied find: ‘/sys/kernel/tracing’: Permission denied find: ‘/sys/kernel/debug’: Permission denied find: ‘/sys/fs/pstore’: Permission denied find: ‘/sys/fs/bpf’: Permission denied find: ‘/run/lock/lvm’: Permission denied find: ‘/run/systemd/inaccessible/dir’: Permission denied find: ‘/run/systemd/propagate/systemd-udevd.service’: Permission denied find: ‘/run/systemd/propagate/systemd-resolved.service’: Permission denied find: ‘/run/systemd/propagate/systemd-networkd.service’: Permission denied find: ‘/run/systemd/propagate/irqbalance.service’: Permission denied find: ‘/run/systemd/propagate/systemd-logind.service’: Permission denied find: ‘/run/systemd/propagate/chrony.service’: Permission denied find: ‘/run/systemd/propagate/polkit.service’: Permission denied find: ‘/run/systemd/propagate/ModemManager.service’: Permission denied find: ‘/run/systemd/propagate/fwupd.service’: Permission denied find: ‘/run/lvm’: Permission denied find: ‘/run/cryptsetup’: Permission denied find: ‘/run/multipath’: Permission denied find: ‘/run/screen/S-bandit20’: Permission denied find: ‘/run/sudo’: Permission denied find: ‘/run/user/11008’: Permission denied find: ‘/run/user/11005’: Permission denied find: ‘/run/user/11006/systemd/inaccessible/dir’: Permission denied find: ‘/run/user/11016’: Permission denied find: ‘/run/user/11012’: Permission denied find: ‘/run/user/11004’: Permission denied find: ‘/run/user/11000’: Permission denied find: ‘/run/user/11024’: Permission denied find: ‘/run/user/11022’: Permission denied find: ‘/run/user/11003’: Permission denied find: ‘/run/user/11001’: Permission denied find: ‘/run/user/11002’: Permission denied find: ‘/run/user/11023’: Permission denied find: ‘/run/user/11011’: Permission denied find: ‘/run/user/11014’: Permission denied find: ‘/run/user/11020’: Permission denied find: ‘/run/user/11013’: Permission denied find: ‘/run/user/11007’: Permission denied find: ‘/run/user/11029’: Permission denied find: ‘/run/user/11025’: Permission denied find: ‘/run/user/11032’: Permission denied find: ‘/run/user/11019’: Permission denied find: ‘/run/user/11031’: Permission denied find: ‘/run/user/11021’: Permission denied find: ‘/run/user/11015’: Permission denied find: ‘/run/user/11009’: Permission denied find: ‘/run/user/11026’: Permission denied find: ‘/run/user/11017’: Permission denied find: ‘/run/chrony’: Permission denied find: ‘/run/udisks2’: Permission denied

仔细看是找到了，这一堆没有访问权限里/var/lib/dpkg/info/bandit7.password

find / -type f -user bandit7 -group bandit6 -size 33c 2> /dev/null

/var/lib/dpkg/info/bandit7.password

2> /dev/null

这个部分的作用是将错误输出（即 stderr）重定向到 /dev/null，这是一个特殊的设备文件，任何写入它的数据都会被丢弃。使用这个重定向后，所有的错误消息（例如 Permission denied 或 No such file or directory）都会被忽略，不会显示出来。

cat /var/lib/dpkg/info/bandit7.password

morbNTDkSW6jIlUc0ymOdMaLnOlFVAaj

Level 7 → Level 8

The password for the next level is stored in the file data.txt next to the word millionth【下一级的密码存储在文件data.txt 在单词 millionth 旁边】

grep '^millionth' data.txt

dfwvzFQi4mU0wfNbFOe9RoWskMLg7eEc

Level 8 → Level 9

The password for the next level is stored in the file data.txt and is the only line of text that occurs only once【下一级的密码存储在文件data.txt 并且是唯一只出现一次的文本行】

cat data.txt | sort | uniq -u

4CKMh1JI91bUIZZPXDqGanal4xvAg0JM

Level 9 → Level 10

The password for the next level is stored in the file data.txt in one of the few human-readable strings, preceded by several ‘=’ characters.【下一级的密码存储在文件data.txt 在为数不多的人类可读字符串之一中，前面有几个 '=' 字符。】

cat data.txt | strings

FGUW5ilLVJrxX9kMYMmlN4MgbpfMiqey

Shell Demo

neofetch

查看运行的系统，是一个需要安装的软件

# ls  # cd  # ls -a  # vim :wq  # cat  # htop  # man htop

Editors

Nano
Vim(vimtutor)
Emacs(Emacs Tutorial)
(NotePad)

Try running (editor of choice)(file)

Shell Commands

Basic structure of a command is

[command][flags][arguments]

RTFM!man(command)
Google is also your best friend.

Common Shell Commands

cd - change directory
ls - list directory
cat - concatenate and print files
head - read the first 10 lines
less - read larger files
mv - move
cp - copy
rm - delete a file

Beginner Lab 1 - Unix, the Shell, OSS

.tgz 文件实际上是两种文件格式的组合。有时，您会将这些文件视为 .tar.gz。

不过，除非你要求，否则 tar 本身不会压缩文件。这就是 gzip（或 bzip2）的用武之地。gzip 会压缩你的文件，所以 tar + gzip 经常连用。它看起来像这样： file --(tar)--> file.tar --(gzip)--> file.tar.gz.

如果你足够仔细地阅读 tar 文档，你会发现你也可以给命令一个使用 gzip 压缩文件的选项，总共为你节省一行 shell 命令！

tar xvzf b01.tgz #tar：调用 tar 命令（用于打包/解压 .tar 文件）;x：extract（解压文件）;v：verbose（显示解压过程的详细信息）;z：gzip（处理 .gz 压缩文件）;f：file（指定要处理的文件）

pwd

pwd 命令显示当前目录路径，它是实时查询的。

grep -B 2 "http" big_data.txt

chmod +x a_script

UNIX

Evolution of UNIX

OSS Licenses:Legal Jiggery-Pokery

Copyleft(GPL)
"I want to make sure that all versions of GNU remain free." - Stallman(GNU Manifesto)
"a cancer that attaches itself in an intellectual property sense to everything it touches" - Steve Ballmer
Permissive(MIT，BSD，Apache，WTFPL)
Do whatever you want(basically)
choosealicense.com/licenses

参考:

Sysadmin DeCal