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Linux

安装

文本编辑器

Vim

Vim 是 Linux 系统下常用的一款 CLI 文本编辑器。 打开终端 ([Ctrl] + [Alt] + T) 并尝试以下命令：

vim --version

如果提示没有安装，可以通过以下命令下载并安装：

sudo apt install vim

其中 apt 是 Debian/Ubuntu 下的软件包管理命令。 在 CentOS/Fedora 下用 yum 替换。

Shell

sh

sh is a POSIX-compliant command interpreter (shell). It is implemented by re-execing as either bash, dash, or zsh as determined by the symbolic link located at /private/var/select/sh. If /private/var/select/sh does not exist or does not point to a valid shell, sh will use one of the supported shells.

bash --- Bourne-Again SHell

启动方式

根据启动方式，可以将 shell 分为

  • login shell：启动时需要输入用户名、密码（如：登入远程主机），并依次运行
    • 全局脚本 /etc/profile
    • 当前用户脚本 ~/.bash_profile
  • non-login shell：启动时无需输入用户名、密码（如：在 GUI 中打开命令行终端），从主进程继承环境变量，并依次运行
    • 全局脚本 /etc/bash.bashrc
    • 当前用户脚本 ~/.bashrc

样式微调

Ubuntu 默认的终端（/bin/bash）提示格式为

username@hostname:~$

其中 username@hostname 是同一种颜色。 为了更方便地区分 username 与 hostname，可以在终端设置文件 (如 ~/.bashrc) 中修改颜色及格式设置。

在所有 Linux 发行版下，都可以用 Vim 来修改：

vim ~/.bashrc

对于不熟悉 Vim 的新手，可以用任何一款 GUI 文本编辑器进行修改。 例如在 Ubuntu 中，可以用 gedit 代替 Vim：

gedit ~/.bashrc

找到以下内容

if [ "$color_prompt" = yes ]; then
    PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
else
    PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
fi

将其修改为

if [ "$color_prompt" = yes ]; then
    PS1='\[\033[34m\]\u\[\033[00m\]@\[\033[31m\]\h\[\033[00m\]:\[\033[32m\]\w\[\033[00m\]\n\$ '
else
    PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
fi

在 ~/.bashrc 文件中，另一个建议修改的地方是：

# -a 选项会显示隐藏文件的信息，日常使用中是多余的：
alias ll='ls -alF'
# 建议修改为：
alias ll='ls -lF'

保存并退出，然后用 source 命令使其生效 (或重启终端)：

source ~/.bashrc

zsh --- Z SHell

安装及配置：

sudo apt install zsh
# 下载好看的样式：
sh -c "$(wget https://raw.github.com/ohmyzsh/ohmyzsh/master/tools/install.sh -O -)"
# 或手动下载 install.sh，再执行该脚本：
mv install.sh ~/
chmod 755 install.sh
sh -c ./install.sh
# 修改配置：
vim ~/.zshrc

设为默认 shell：

echo $SHELL           # 查看 login shell
chsh -s $(which zsh)  # 更换 login shell
# 退出当前 shell 并重新打开

ssh --- Secure SHell

语法

for 循环

# , 前后不能有空格
for x in {2,3,4}; do echo $x; done
# 或等价的
for ((x = 2; x <= 4; ++x)); do echo $x ; done
# 输出：
2
3
4

嵌套循环：

for x in {2,3}; do for y in {a,b}; do echo $x $y; done; done
# 输出
2 a
2 b
3 a
3 b

参数展开

See 3.5.3 Shell Parameter Expansion for more.

# 假设
for x in p=2*.log ; do echo ${x} ; done
# 输出
p=2_n=10.log
p=2_n=20.log
p=2_n=40.log
p=2_n=80.log
# 则 ${parameter:offset:length}
for x in p=2*.log ; do echo ${x:4:3} ; done
# 输出 x[4, 4+3)
n=1
n=2
n=4
n=8
# 或
for x in p=2*.log ; do echo ${x:(-4)} ; done
for x in p=2*.log ; do echo ${x: -4} ; done
# 均输出
.log
.log
.log
.log
# 替换后缀
for x in p=2*.log ; do echo ${x%.log}.csv ; done
# 输出
p=2_n=10.csv
p=2_n=20.csv
p=2_n=40.csv
p=2_n=80.csv

文件系统操作

locate

Locate files by name.

find

Find files in a directory hierarchy.

# Find files by extension:
    find root_path -name '*.ext'

# Find files matching multiple path/name patterns:
    find root_path -path '**/path/**/*.ext' -or -name '*pattern*'

# Find directories matching a given name, in case-insensitive mode:
    find root_path -type d -iname '*lib*'

# Find files matching a given pattern, excluding specific paths:
    find root_path -name '*.py' -not -path '*/site-packages/*'

# Find files matching a given size range:
    find root_path -size +500k -size -10M

# Run a command for each file (use `{}` within the command to access the filename):
    find root_path -name '*.ext' -exec wc -l {} \;

# Find files modified in the last 7 days and delete them:
    find root_path -daystart -mtime -7 -delete

# Find empty (0 byte) files and delete them:
    find root_path -type f -empty -delete

touch

Change file timestamps, i.e. touch a file.

stat

  • GNU: Display file or file system status.
  • BSD: Display file status.
# Show file properties such as size, permissions, creation and access dates among others:
    stat file

# Same as above but verbose (more similar to Linux's `stat`):
    stat -x file

# Show only octal file permissions:
    stat -f %Mp%Lp file

# Show owner and group of the file:
    stat -f "%Su %Sg" file

# Show the size of the file in bytes:
    stat -f "%z %N" file

du

Show disk usage.

# Show disk usage of current folder:
du -sh
# Show disk usage of Videos:
du -sh Videos/
# Show disk usage of level-1 subfolders in current folder:
du -h --max-depth=1
# Show disk usage of level-1 subfolders in Pictures:
du -h --max-depth=1 Pictures/

数据流操作

cat

Concatenate files and print on the standard output.

head

Output the head (i.e. the first part) of files.

tail

Output the tail (i.e. the last part) of files.

sort

Sort lines of text files.

uniq

Report or omit repeated lines.

sed

Stream editor for filtering and transforming text.

# Replace the first occurrence of a string in a file, and print the result:
    sed 's/find/replace/' filename
# Replace all occurrences of an extended regular expression in a file:
    sed -E 's/regular_expression/replace/g' filename
# Replace all occurrences of a string [i]n a file, overwriting the file (i.e. in-place):
    sed -i 's/find/replace/g' filename
# Replace only on lines matching the line pattern:
    sed '/line_pattern/s/find/replace/' filename
# Print only text between n-th line till the next empty line:
    sed -n 'line_number,/^$/p' filename
# Apply multiple find-replace expressions to a file:
    sed -e 's/find/replace/' -e 's/find/replace/' filename
# Replace separator `/` by any other character not used in the find or replace patterns, e.g. `#`:
    sed 's#find#replace#' filename
# [d]elete the 11th (1-based) line [i]n a file, overwriting the file:
    sed -i '' '11d' filename

awk

A versatile programming language for working on files.

# Print the fifth column (a.k.a. field) in a space-separated file:
    awk '{print $5}' filename
# Print the second column of the lines containing "foo" in a space-separated file:
    awk '/foo/ {print $2}' filename
# Print the last column of each line in a file, using a comma (instead of space) as a field separator:
    awk -F ',' '{print $NF}' filename
# Sum the values in the first column of a file and print the total:
    awk '{s+=$1} END {print s}' filename
# Print every third line starting from the first line:
    awk 'NR%3==1' filename
# Print different values based on conditions:
    awk '{if ($1 == "foo") print "Exact match foo"; else if ($1 ~ "bar") print "Partial match bar"; else print "Baz"}' filename
# Print all lines where the 10th column value equals the specified value :
    awk '($10 == value)'
# Print all the lines which the 10th column value is between a min and a max :
    awk '($10 >= min_value && $10 <= max_value)'

xargs

Execute a command with piped arguments coming from another command, a file, etc. The input is treated as a single block of text and split into separate pieces on spaces, tabs, newlines and end-of-file.

# Run a command using the input data as arguments:
    arguments_source | xargs command
# Run multiple chained commands on the input data:
    arguments_source | xargs sh -c "command1 && command2 | command3"
# Delete all files with a `.backup` extension (`-print0` uses a null character to split file names, and `-0` uses it as delimiter):
    find . -name '*.backup' -print0 | xargs -0 rm -v
# Execute the command once for each input line, replacing any occurrences of the placeholder (here marked as `_`) with the input line:
    arguments_source | xargs -I _ command _ optional_extra_arguments
# Parallel runs of up to `max-procs` processes at a time; the default is 1. If `max-procs` is 0, xargs will run as many processes as possible at a time:
    arguments_source | xargs -P max-procs command

grep

Print lines that match patterns.

# Search for a pattern within a file:
    grep "search_pattern" path/to/file
# Search for an exact string (disables regular expressions):
    grep --fixed-strings "exact_string" path/to/file
# Search for a pattern in all files recursively in a directory, showing line numbers of matches, ignoring binary files:
    grep --recursive --line-number --binary-files=without-match "search_pattern" path/to/directory
# Use extended regular expressions (supports `?`, `+`, `{}`, `()` and `|`), in case-insensitive mode:
    grep --extended-regexp --ignore-case "search_pattern" path/to/file
# Print 3 lines of context around, before, or after each match:
    grep --context|before-context|after-context=3 "search_pattern" path/to/file
# Print file name and line number for each match:
    grep --with-filename --line-number "search_pattern" path/to/file
# Search for lines matching a pattern, printing only the matched text:
    grep --only-matching "search_pattern" path/to/file
# Search stdin for lines that do not match a pattern:
    cat path/to/file | grep --invert-match "search_pattern"

wc

Print newline, word, and byte counts for each file.

# Count [l]ines in file:
    wc -l file
# Count [w]ords in file:
    wc -w file
# Count [c]haracters (bytes) in file:
    wc -c file
# Count characters in file (taking [m]ulti-byte character sets into account):
    wc -m file
# Use standard input to count lines, words and characters (bytes) in that order:
    find . | wc

tee

Read from standard input and write to standard output and files.

# Copy standard input to each file, and also to standard output:
    echo "example" | tee path/to/file
# Append to the given files, do not overwrite:
    echo "example" | tee -a path/to/file
# Print standard input to the terminal, and also pipe it into another program for further processing:
    echo "example" | tee /dev/tty | xargs printf "[%s]"
# Create a directory called "example", count the number of characters in "example" and write "example" to the terminal:
    echo "example" | tee >(xargs mkdir) >(wc -c)

>, >>

名称 覆盖 追加
stdout 1> filename 1>> filename
stderr 2> filename 2>> filename 
# 正常信息、错误信息 均输出到 屏幕
$ find ~/.. -name .bash_history
# 正常信息 输出到 stdout.txt 文件，错误信息 输出到 屏幕
$ find ~/.. -name .bash_history > stdout.txt
# 正常信息 输出到 stdout.txt 文件，错误信息 输出到 stderr.txt 文件
$ find ~/.. -name .bash_history > stdout.txt 2> stderr.txt
# 正常信息、错误信息 均输出到 stdout_stderr.txt 文件
$ find ~/.. -name .bash_history 2>&1 stdout_stderr.txt

系统管理

设备管理

# 查看 CPU 信息
cat /proc/cpuinfo | grep "model name"
# 查看 RAM 信息
cat /proc/meminfo | grep Mem

权限管理

id - display user identity

chmod - change a file's mode

umask - set file mode creation mask

su - run a command with substitute user

sudo - execute a command as another user

chown - change a file's owner

chgrp - change a file's group

passwd - change user password

进程管理

基本概念

本节的程序 (program) 特指（存储在磁盘中的）可执行文件，而进程 (process) 则是（被操作系统加载到内存中的）某个程序的运行实例。 操作系统在加载一个程序使其成为一个进程时，会为其分配一个 Process ID (PID) 并附上进程触发者的 User ID (UID) 及 Group ID (GID)。

进程之间可能存在依赖关系，即一个进程由另一个进程触发。

  • 被依赖者（即触发者）被称为亲进程 (parent process)。
  • 依赖者（即被触发者）被称为子进程 (child process)。
  • 子进程将亲进程的 UID、GID 继承下来，并以亲进程的 PID 作为自己的 Parent Process ID (PPID)。

查看进程

命令 功能
ps -l 只显示与自己相关的进程
ps aux 显示所有进程
pstree 显示进程依赖关系
pstree -p 12345 只显示 PID 为 12345 的那个进程的亲代及后代
pstree -u user 只显示用户名为 user 的那些进程的亲代及后代
top 动态显示所有进程状态（按 q 退出）
top -o +cpu -s 3 -n 4 CPU 升序、采样周期 3 秒、最多 4 个进程

管理进程

命令 功能
kill -9 12345 强制关闭 PID 为 12345 的那个进程
kill -15 12345 正常关闭 PID 为 12345 的那个进程
killall -9 process 强制关闭名为 process 的那些进程
killall -s -9 process 显示但不执行操作

管理任务

由同一个 shell 进程触发的子进程称为任务 (job)。 若系统只提供了一个 shell 进程，则用户通常需要将任务在前台 (foreground) 与后台 (background) 之间来回切换，以便让多个任务同时运行。

⚠️ 这里的前后台是相对于当前 shell 进程而言的；若这个 shell 进程是远程主机提供的，则退出 shell 意味着退出所有后台任务（仍在后台的任务会阻断 shell 的退出）。 《利用 SSH 访问远程 Linux 主机》介绍了如何访问远程主机以及在远程主机的后台运行任务。

命令 功能
top & 在后台启动并运行 top
Ctrl + Z 将当前任务暂停并移入后台
jobs 显示当前的后台任务
fg %2 将任务 2 从后台移到前台运行
bg %2 令任务 2 在后台运行
kill -l 列出可用的信号
kill -2 %2 相当于在后台按下 Ctrl + C
kill -9 %2 强制结束并删除任务 2
kill -15 %2 按正常步骤结束任务 2
kill -19 %2 相当于在后台按下 Ctrl + Z

以下示例演示了表中主要命令的用法：

  1. 在后台启动并运行一个任务： 
    $ top &
[1] 60137
    返回值 [1] 为其任务编号 (job number)，60137 为 PID。
  2. 启动一个需要运行很长时间的任务，按 Ctrl + Z 将其暂停并移入后台： 
    $ find / > temp.txt
# 需要运行很长时间（除非该系统几乎没有被使用过）
# 按 `Ctrl + Z` 将进程暂停并移入后台
[2]+  Stopped                 find / > temp.txt
  3. 此时已有两个后台任务，可用 jobs 查看： 
    $ jobs
[1]-  Stopped                 vim
[2]+  Stopped                 find / > temp.txt
$ jobs -l
[1]- 60137 Stopped (tty output): 22top
[2]+ 60141 Suspended: 18           find / > temp.txt
    其中 + 与 - 分别表示最后一个与倒数第二个被移入后台的任务。
  4. 令（停止的）任务在前台或后台运行： 
    $ fg %2  # `find ~ > temp.txt` 在前台恢复运行
# 输出几乎不会停止，按 `Ctrl + Z` 移入后台
$ bg %2  # `find ~ > temp.txt` 在后台恢复运行
$ jobs
[1]+  Stopped                 top
[2]-  Running                 find ~ > temp.txt &
  5. 向后台任务发送信号： 
    $ kill %1  # 正常结束 任务[1]
$ jobs  # 短时间内 任务[1] 的状态变为 Terminated
[1]-  Terminated: 15          top
[2]+  Stopped                 find / > temp.txt
$ jobs  # 较长时间后，只剩下 任务[2]
[2]+  Stopped                 find / > temp.txt
$ kill -2 %2  # 在后台 Ctrl + C 任务[2]
$ jobs  # 短时间内 任务[2] 的状态变为 Interrupt
[2]+  Interrupt: 2            find / > temp.txt

网络管理

ifconfig - configure a network interface

$ ifconfig  # 查询所有网卡
eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.10  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 2002:a86:4beb:0:e41:f0c6:4354:e13  prefixlen 64  scopeid 0x0<global>
        inet6 2002:a86:4beb:0:42fa:7a9f:24a8:eee2  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::126e:97a8:b5b9:4395  prefixlen 64  scopeid 0x20<link>
        ether 44:37:e6:bb:ec:a3  txqueuelen 1000  (Ethernet)
        RX packets 235305  bytes 332897613 (332.8 MB)
        RX errors 0  dropped 108  overruns 0  frame 0
        TX packets 59627  bytes 4690785 (4.6 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 20  memory 0xf7100000-f7120000  

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 6633  bytes 576493 (576.4 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 6633  bytes 576493 (576.4 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0


$ ifconfig eno1  # 查询指定网卡
eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.10  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 2002:a86:4beb:0:e41:f0c6:4354:e13  prefixlen 64  scopeid 0x0<global>
        inet6 2002:a86:4beb:0:42fa:7a9f:24a8:eee2  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::126e:97a8:b5b9:4395  prefixlen 64  scopeid 0x20<link>
        ether 44:37:e6:bb:ec:a3  txqueuelen 1000  (Ethernet)
        RX packets 235397  bytes 332910768 (332.9 MB)
        RX errors 0  dropped 109  overruns 0  frame 0
        TX packets 59668  bytes 4698974 (4.6 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 20  memory 0xf7100000-f7120000  


$ sudo ifconfig eno1 192.168.1.111  # 设置指定网卡（除 IPv4 地址外，采用默认值）
$ sudo ifconfig eno1 192.168.1.111 netmask 255.255.255.0 mtu 8000  # 更精细的设置

ip - show / manipulate routing, network devices, interfaces and tunnels

$ ip -s link show  # 显示所有网卡的信息及统计（`-s`）
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    RX: bytes  packets  errors  dropped overrun mcast   
    670613     7532     0       0       0       0       
    TX: bytes  packets  errors  dropped carrier collsns 
    670613     7532     0       0       0       0       
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 2000 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 44:37:e6:bb:ec:a3 brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast   
    334900636  240457   0       127     0       6420    
    TX: bytes  packets  errors  dropped carrier collsns 
    4964034    61586    0       0       0       0       
    altname enp0s25

$ ip addr show eno1  # 显示指定网卡的地址（`inet` 及 `inet6`）
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 44:37:e6:bb:ec:a3 brd ff:ff:ff:ff:ff:ff
    altname enp0s25
    inet 192.168.1.10/24 brd 192.168.1.255 scope global dynamic noprefixroute eno1
       valid_lft 85979sec preferred_lft 85979sec
    inet6 2002:a86:4beb:0:7aa1:88c7:e85:b3db/64 scope global temporary dynamic 
       valid_lft 2370sec preferred_lft 1770sec
    inet6 2002:a86:4beb:0:e41:f0c6:4354:e13/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2370sec preferred_lft 1770sec
    inet6 fe80::126e:97a8:b5b9:4395/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

$ sudo ip link set eno1 up|down   # 开关指定网卡
$ sudo ip link set eno1 mtu 8000  # 调整个别参数

ping - send ICMP ECHO_REQUEST to network hosts

$ ping bing.com  # 持续测试，直到 Ctrl + C 停止
$ ping -c 4 bing.com  # 测试 4 次
PING china.bing123.com (202.89.233.100) 56(84) bytes of data.
64 bytes from 202.89.233.100 (202.89.233.100): icmp_seq=1 ttl=115 time=3.59 ms
64 bytes from 202.89.233.100 (202.89.233.100): icmp_seq=2 ttl=115 time=3.27 ms
64 bytes from 202.89.233.100 (202.89.233.100): icmp_seq=3 ttl=115 time=3.50 ms
64 bytes from 202.89.233.100 (202.89.233.100): icmp_seq=4 ttl=115 time=3.25 ms

--- china.bing123.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 3.252/3.402/3.589/0.144 ms

traceroute - print the route packets trace to network host

$ traceroute bing.com
$ traceroute -w 1 -n -T bing.com  # 等待 1s、不解析域名、用 TCP 检测
traceroute to bing.com (204.79.197.200), 30 hops max, 60 byte packets
 1  192.168.1.1  0.231 ms  17.699 ms  17.682 ms
 2  10.134.74.1  139.197 ms  139.177 ms  139.686 ms
 3  10.254.1.1  139.660 ms  139.638 ms  139.622 ms
 4  211.71.0.29  139.597 ms  139.581 ms  139.567 ms
 5  106.120.221.209  139.592 ms  139.576 ms  139.512 ms
 6  * * *
 7  * * *
 8  * * *
 9  * * *
10  * * *
11  * * *
12  * * *
13  * * *
14  204.79.197.200  260.581 ms *  260.553 ms

host - DNS lookup utility

$ host bing.com
bing.com has address 13.107.21.200
bing.com has address 204.79.197.200
bing.com has IPv6 address 2620:1ec:c11::200
bing.com mail is handled by 10 bing-com.mail.protection.outlook.com.

nslookup - query Internet name servers interactively

$ nslookup bing.com
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
Name:   bing.com
Address: 204.79.197.200
Name:   bing.com
Address: 13.107.21.200
Name:   bing.com
Address: 2620:1ec:c11::200

netstat - show network status