Unlock Linux Mastery: Essential Commands, Shell Basics, and System Administration Guide

Foreword

Learning Linux is essential for any programmer. Front‑end developers have fewer opportunities to work with Linux compared to back‑end developers, so it is often overlooked, but mastering Linux is a must‑have skill for developers.

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The author uses an Alibaba Cloud ECS (the cheapest type) running CentOS 7.7 64‑bit. You can also install CentOS on a virtual machine on your own computer; the installation tutorials are widely available on Google.

Linux Basics

Operating System

The operating system, abbreviated as OS, is the first layer of software on top of hardware, acting as a bridge between hardware and other software.

The OS controls program execution, manages system resources, provides basic computing functions such as memory management and prioritizing resource allocation, and offers basic service programs.

What is Linux

Difference Between Linux Kernel and Linux Distributions

Linux

kernel is maintained by Linus Torvalds and provides hardware abstraction, disk and file system control, and multitasking. Linux distribution is the kernel plus a collection of common software packages, forming a complete operating system.

Summary: The true Linux refers to the kernel, while the commonly mentioned Linux usually means a complete distribution.

Linux vs Windows

Stable and efficient.

Free (or low‑cost).

Fewer vulnerabilities and fast patches.

Multitasking and multi‑user.

More secure user and file permission policies.

Suitable for embedded systems with small kernels.

Relatively low resource consumption.

Linux System Types

Red Hat Enterprise Linux ( RHEL) – widely used in production, commercial.

Fedora – community edition released by Red Hat, serves as a testing ground for RHEL.

CentOS – free rebuild of RHEL, widely used.

Deepin – Chinese distribution focusing on integration and configuration of open‑source products.

Debian – stable, secure, widely adopted abroad.

Ubuntu – Debian‑based, excellent desktop compatibility, also suitable for servers.

Connecting to an Alibaba Cloud Server via Terminal

Execute ssh [email protected] and enter the password to log in to the remote server. From now on you can operate the remote server from your local computer.

The black panel is the Shell (command‑line environment). ssh root@xxx is a command that must be run inside a Shell.

Shell

The word Shell literally means “shell”; it is the interface between the user and the kernel, providing a command prompt for user input. Shell is a program that offers a dialog environment with a single prompt, also called a command‑line interface ( CLI). Shell interprets user commands and passes them to the OS for execution, returning results. Shell is a toolbox that provides various utilities for interacting with the OS.

Types of Shells

Many programs can serve as a shell as long as they provide a command‑line environment.

Bourne Shell ( sh)

Bourne Again Shell ( bash) – the most commonly used shell.

C Shell ( csh)

TENEX C Shell ( tcsh)

Korn Shell ( ksh)

Z Shell ( zsh)

Friendly Interactive Shell ( fish)

On macOS, the default shell is bash.

Run echo $SHELL to view the current shell. Use cat /etc/shells to list all installed shells.

Commands

Command Prompt

After entering the command line, the prompt usually ends with a dollar sign $. For example, running pwd displays the current directory:

root@iZm5e8dsxce9ufaic7hi3uZ ~# pwd
/root

Explanation of the output: root – username. iZm5e8dsxce9ufaic7hi3uZ – hostname. ~ – home directory. # – indicates root privileges (ordinary users see $). whoami shows the current user; hostname shows the host name.

Commands such as creating or deleting users will be covered later; for now we use the root user for demonstration.

Note: root is the superuser with full system permissions.

Command Syntax

command parameters

Examples of common parameters: -i – ignore case. -n – show line numbers. -v – show lines that do NOT match. -r – recursive search.

Advanced Usage

grep

can use regular expressions:

grep -E path /etc/profile          # exact match
grep -E ^path /etc/profile         # lines starting with "path"
grep -E [Pp]ath /etc/profile       # case‑insensitive match

Sorting

Sort lines in a file: sort name.txt Common options: -o – write output to a new file. -r – reverse order. -R – random order. -n – numeric sort.

Word Count

wc

reports lines, words, and bytes: wc name.txt Options: -l – line count only. -w – word count only. -c – byte count only. -m – character count only.

Unique Lines

uniq

removes consecutive duplicate lines:

uniq name.txt          # remove duplicates and print
uniq name.txt uniq.txt # save result to uniq.txt

Options: -c – prefix lines by occurrence count. -d – show only duplicated lines.

Cut

Extract sections of each line:

cut -c 2-4 name.txt          # characters 2 to 4 of each line
cut -d , -f 1 notes.csv      # first field using comma as delimiter

Options: -d – set delimiter. -f – select field numbers.

Redirection, Pipes, and Streams

Linux commands can send output to the terminal, a file, or another command. The three standard streams are stdin, stdout, and stderr.

Redirection

Output Redirection >

Redirect command output to a new file (overwrites if the file exists):

cut -d , -f 1 notes.csv > name.csv

Append Redirection >>

Append output to the end of a file (creates the file if it does not exist):

cut -d , -f 1 notes.csv >> name.csv

Error Redirection 2> and 2>>

Redirect standard error to a file (overwrite or append):

cat not_exist_file.csv > res.txt 2> errors.log
cat not_exist_file.csv >> res.txt 2>> errors.log

Redirect Both Streams 2>&1

cat not_exist_file.csv > res.txt 2>&1   # overwrite both
cat not_exist_file.csv >> res.txt 2>&1 # append both

Input Redirection <

cat < name.csv

Here‑Document <<

sort -n << END
...input lines...
END

Pipes |

Pass the output of one command as input to another:

cut -d , -f 1 name.csv | sort > sorted_name.txt

Streams

A stream is a flow of data (often binary) that can be redirected or piped between commands.

Viewing Processes

w

06:31:53 up 25 days, 9:53, 1 user, load average: 0.00, 0.01, 0.05
USER   TTY   FROM      LOGIN@   IDLE   JCPU   PCPU WHAT
root   pts/0 118.31.243.53 05:56   1.00s  0.02s  0.00s w 06:31:53

ps

PID TTY          TIME CMD
1793 pts/0    00:00:00 bash
4756 pts/0    00:00:00 ps

Common options: -ef, -efH, -u, -aux, --sort -pcpu, -axjf.

top

top - 07:20:07 up 25 days, 10:41, 1 user, load average: 0.30, 0.10, 0.07
Tasks: 67 total, 1 running, 66 sleeping
%Cpu(s): 0.7 us, 0.3 sy, 99.0 id
KiB Mem : 1882072 total, 552148 free, 101048 used, 1228876 buff/cache
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
956 root 10 -10 133964 15848 10240 S 0.7 0.8 263:13.01 AliYunDun

kill

kill 956               # terminate process 956
kill -9 7291           # force kill process 7291

Managing Processes

Process States

R

– running. S – sleeping (interruptible). D – uninterruptible sleep. Z – zombie (terminated but not reaped). T – stopped (signal‑stopped).

Foreground vs Background

Append & to run a command in the background. Use bg to resume a stopped job, fg to bring it to the foreground, and jobs to list background jobs.

nohup

Run a command immune to hang‑up signals:

nohup cp name.csv name-copy.csv &

bg and fg

bg %1   # resume job 1 in background
fg %1   # bring job 1 to foreground

Daemons

Daemons are background services whose parent process is PID 1 ( systemd). They run continuously and provide core system functions.

systemd

ps -aux | grep systemd
root 1 0.0 0.2 51648 3852 ? Ss Feb01 1:50 /usr/lib/systemd/systemd --switched-root --system --deserialize 22

Common systemctl commands: start, stop, restart, status, reload, enable, disable, is-enabled, list-unit-files --type=service.

File Compression and Archiving

tar

Create an archive: tar -cvf archive.tar file1 file2 file3 List contents: tar -tf archive.tar Append files: tar -rvf archive.tar file.txt Extract:

tar -xvf archive.tar

gzip / gunzip

gzip archive.tar
gunzip archive.tar.gz

Tar + Gzip

tar -zcvf archive.tar.gz folder/   # create and compress
tar -zxvf archive.tar.gz          # extract

zcat , zless , zmore

zcat archive.tar.gz

zip / unzip

Install: yum install zip unzip Compress and extract:

zip -r sort.zip sort/
unzip archive.zip
unzip -l archive.zip

Compiling and Installing Software

When a package is not available via yum, compile from source:

Download source code.

Extract the archive.

Run ./configure to check dependencies.

Run make to compile.

Run make install to install.

Example: compile htop from source.

Networking

ifconfig

Show network interfaces (install net-tools if missing):

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
    inet 172.31.24.78 netmask 255.255.240.0 broadcast 172.31.31.255
    ether 00:16:3e:04:9c:cd txqueuelen 1000 (Ethernet)
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
    inet 127.0.0.1 netmask 255.0.0.0 (Loopback)

host

Install with yum install bind-utils. Resolve names and IPs:

host github.com
host 13.229.188.59

SSH

Connect to a remote server: ssh [email protected] # default port 22 Configure ~/.ssh/config for shortcuts:

Host lion
    HostName 172.x.x.x
    Port 22
    User root

After configuration, connect with ssh lion.

Key‑Based (Password‑less) Login

Generate a key pair with ssh-keygen (creates ~/.ssh/id_rsa and id_rsa.pub).

Copy the public key to the server with ssh-copy-id [email protected].

Now ssh [email protected] logs in without a password.

wget

Download files from the command line:

wget http://www.minjieren.com/wordpress-3.1-zh_CN.zip

Use -c to continue interrupted downloads.

Backup

scp

Secure copy files between hosts:

scp file.txt [email protected]:/root
scp [email protected]:/root/file.txt ./file.txt

rsync

Synchronize directories (install with yum install rsync).

rsync -arv Images/ backups/
rsync -arv Images/ [email protected]:backups/

Use --delete to remove files that no longer exist in the source.

System Control

Shutdown, reboot, or power off:

halt      # requires root
reboot    # requires root
poweroff  # can be run by any user

Vim Editor

What Is Vim?

Vim is an enhanced version of vi, offering powerful features such as code completion, compilation, and error navigation. It is a favorite editor among Unix users alongside Emacs.

Vim Modes

Normal (interactive) mode – default mode for navigation and commands.

Insert mode – for entering text (enter with i, a, o, etc.).

Command mode – accessed by : to run commands like wq, q!, etc.

Visual mode – for selecting text (character, line, or block).

Normal Mode

Use h j k l or arrow keys to move the cursor.

Insert Mode

Press i to insert before the cursor, a after, o on a new line below, Esc to return to Normal mode.

Command Mode

Press : then type commands such as w (write), q (quit), wq (write and quit).

Visual Mode

Press v for character selection, V for line selection, Ctrl+v for block selection. Use d to delete, I to insert at the beginning of each selected line, u / U to change case.

Basic Operations

Open Vim: vim filename (creates the file if it does not exist).

Insert text: press i then type.

Move cursor: h left, j down, k up, l right, 0 line start, $ line end, w next word.

Delete character: x (prefix with a number to delete multiple).

Delete line: dd (prefix with a number to delete multiple lines).

Delete word: dw (prefix with a number for multiple).

Copy line: yy; copy word: yw.

Paste: p (prefix with a number to paste multiple times).

Replace a character: r then the new character.

Undo: u (prefix with a number for multiple undos); redo: Ctrl+r.

Jump to line: gg (first line), G (last line), or 7gg (line 7).

Search: /pattern then n (next) or N (previous). Use ? to search backward.

Search and replace: :%s/old/new/g for whole file, or :s/old/new/g for current line.

Merge files: :r filename inserts the file at the cursor.

Split windows: :sp file (horizontal) or :vsp file (vertical). Navigate splits with Ctrl+w followed by h/j/k/l or Ctrl+w Ctrl+w. Resize with Ctrl+w + / -, equalize with =, close with q, close others with o.

Run external commands: :!ls executes ls in the shell.

Vim Configuration

Create a ~/.vimrc file to make settings permanent. Example:

set number          " show line numbers
syntax on           " enable syntax highlighting
set showcmd         " display incomplete commands
set ignorecase      " case‑insensitive search
set mouse=a         " enable mouse support

Customize further by adding plugins or additional options.

Conclusion

After reading this article you should have a more complete understanding of Linux and be able to use its core commands, manage processes, handle files, and edit efficiently with Vim.

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References

[1] https://bintray.com/htop/source/download_file?file_path=htop-3.0.0.tar.gz