Master Linux Command Line: Essential Tips and Tricks for System Operations

1. Commands

1.1 Command Prompt

After entering the command line environment, the user sees the shell prompt, which usually ends with a dollar sign ($) indicating where to type commands.

1.2 Command Syntax

command parameters

Short and long options

ls -a            # a is short for "all"
ls -al           # all files + long listing
ls --all         # long form of -a
ls --reverse --all
ls --all -l

Option values

command -p 10   # e.g., ssh root@host -p 22
command --parameters=10

2. Shortcuts

Before learning Linux commands, master these shortcuts that will be used throughout your Linux journey.

Use ↑ ↓ to scroll through command history.

Tab completes commands or parameters.

Ctrl+R searches command history.

Ctrl+L clears the screen.

Ctrl+C aborts the current command.

Ctrl+U cuts from cursor to line start.

Ctrl+K cuts from cursor to line end.

Ctrl+W cuts the word left of the cursor.

Ctrl+Y pastes what was cut with Ctrl+U/K/W.

Ctrl+A moves cursor to line start.

Ctrl+E moves cursor to line end.

Ctrl+D closes the shell session.

3. Files and Directories

3.1 File Organization

3.2 Viewing Paths

pwd – displays the current directory path.

# pwd
/root

which – shows the location of an executable.

A command is essentially an executable program.

3.3 Browsing and Switching Directories

ls – lists files and directories.

Common options

-a shows all files, including hidden ones.

-l shows a detailed list.

-h makes sizes human‑readable.

-t sorts by modification time.

-i shows the inode number.

cd – change directory ("change directory" abbreviation).

cd /        # go to root directory
cd ~        # go to home directory
cd ..       # go to parent directory
cd ./home   # go to ./home
cd /home/lion # go to /home/lion
cd          # without arguments, goes to home

Note: pressing Tab once after cd /home auto‑completes the path; pressing twice lists possible directories.

du – shows directory size information.

Common options

-h human‑readable.

-a includes file sizes.

-s shows only total size.

3.4 Creating Files

cat – displays entire file content (good for small files). cat cloud-init.log less – paginated view for large files. less cloud-init.log Quick operations

Space – forward one page.

b – back one page.

Enter – forward one line.

y – back one line.

↑/↓ – move one line.

d – forward half a page.

u – back half a page.

q – quit.

= – show current line numbers and details.

h – help.

/ – search (n for next, N for previous, supports regex).

head – shows the first few lines (default 10). head cloud-init.log Option -n specifies number of lines, e.g., head -n 2 cloud-init.log.

tail – shows the last few lines (default 10). tail cloud-init.log Option -n specifies number of lines; -f follows the file, optionally with -s to set interval.

touch – creates an empty file. touch new_file mkdir – creates a directory. mkdir new_folder Option -p creates parent directories as needed.

3.5 Copying and Moving Files

cp – copy files.

cp file file_copy
cp file one
cp file one/file_copy
cp *.txt folder   # copy all .txt files to folder

Option -r copies directories recursively.

mv – move or rename files.

mv file one
mv new_folder one
mv *.txt folder
mv file new_file

3.6 Deleting Files and Links

rm – remove files or directories (no recycle bin).

rm new_file
rm f1 f2 f3

Common options: -i ask for confirmation, -f force, -r recursive (e.g., rm -rf).

ln – create links.

Linux stores a file's name list separately from its content; each name points to an inode.

Two link types:

Hard link – shares the same inode; changes affect both names. Only files (not directories) can be hard‑linked.

Soft link (symbolic link) – similar to Windows shortcuts; points to a path.

ln file1 file2          # hard link
ln -s file1 file2       # soft link

View links with ls -l:

# ls -l
lrwxrwxrwx 1 root root 5 Jan 14 06:41 file2 -> file1

3.7 File Permissions

chmod – change access permissions. chmod 740 file.txt Option -R applies recursively.

Permission string example: drwxr-xr-x means a directory where owner has read/write/execute, group has read/execute, others have read/execute.

Numeric mode explanation:

chmod 640 hello.c   # 6=4+2+0 (owner rw), 4=read for group, 0=no permissions for others
# results in -rw-r-----

Symbolic mode example:

chmod u+rx file
chmod g+r file
chmod o-r file
chmod u=rwx,g=r,o=- file

4. Users and Permissions

4.1 Users

Linux is multi‑user. The special root user has full privileges.

Regular users have limited permissions; sudo elevates privileges temporarily.

sudo – run a command as root. sudo date useradd – add a new user; passwd – set a user's password.

useradd lion
passwd lion

userdel – delete a user (option -r also removes home directory).

userdel lion
userdel lion -r

su – switch user.

sudo su          # become root
su lion          # become lion
su -             # become root with login environment

4.2 Group Management

Each user belongs to a primary group; groups can be created and managed.

groupadd – create a group. groupadd friends groupdel – delete a group. groupdel foo groups – list groups a user belongs to. groups lion usermod – modify user attributes.

-l rename user.

-g change primary group.

-G add secondary groups (use -a -G to append).

chgrp – change a file's group. chgrp bar file.txt chown – change file owner (option -R for recursive).

chown lion file.txt
chown lion:bar file.txt
chown -R lion:lion /home/frank

4.3 File Permission Management

chmod – modify file permissions. chmod 740 file.txt Common option: -R for recursive changes.

5. Finding Files

locate

Searches a database of filenames.

yum -y install mlocate
updatedb
locate file.txt
locate fil*.txt

Note: newly created files are not in the database until updatedb runs.

find

Searches the actual filesystem; very powerful.

find /path -name "file.txt"
find . -name "syslog"
find / -size +10M
find . -name "*.txt" -atime -7
find . -type f -name "file"
find . -type d -name "dir"
find *.txt -printf "%p - %u
"
find *.c -delete
find *.c -exec chmod 600 {} \;

6. Software Repositories

Linux packages are distributed as archives (.rpm for Red Hat, .deb for Debian). The yum tool manages packages on CentOS/Red Hat.

yum update | yum upgrade – update packages.

yum search xxx – search packages.

yum install xxx – install.

yum remove xxx – remove.

To switch to a domestic mirror (e.g., Alibaba Cloud):

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
yum makecache

7. Reading Manuals

Use man to view command manuals.

sudo yum install -y man-pages
mandb

Sections of a man page (example man pwd):

NAME – command name and brief description.

SYNOPSIS – usage syntax.

DESCRIPTION – detailed description and options.

SEE ALSO – related commands.

Quick help with command --help or command -h.

8. Linux Advanced Topics

Text Operations

grep

Searches for patterns in files.

grep text file
grep -i path /etc/profile
grep -n path /etc/profile
grep -v path /etc/profile
grep -r hello /etc

Extended regex with -E:

grep -E path /etc/profile
grep -E ^path /etc/profile
grep -E [Pp]ath /etc/profile

sort

Sorts lines of a file.

sort name.txt
sort -o name_sorted.txt name.txt
sort -r name.txt
sort -R name.txt
sort -n numbers.txt

wc

Word count – lines, words, bytes.

wc name.txt
wc -l name.txt
wc -w name.txt
wc -c name.txt
wc -m name.txt

uniq

Removes duplicate consecutive lines.

uniq name.txt
uniq -c name.txt
uniq -d name.txt

cut

Extracts sections from each line.

cut -c 2-4 name.txt
cut -d , -f 1 name.txt

9. Redirection, Pipes, and Streams

Standard streams: stdin, stdout, stderr.

Redirection

Output redirection:

command > file      # overwrite
command >> file     # append
command 2> err.log  # redirect stderr
command > out.txt 2>&1   # both stdout and stderr to file

Input redirection:

command < file
command << END
...content...
END

Pipes

Connect commands; output of left becomes input of right.

cut -d , -f 1 name.csv | sort > sorted_name.txt
du | sort -nr | head
grep log -Ir /var/log | cut -d : -f 1 | sort | uniq

Streams

Data flows as a stream; concepts used in many languages (e.g., Angular pipes, Node.js streams).

10. Viewing Processes

w

Shows who is logged in and what they are doing.

# w
06:31:53 up 25 days, 9:53, 1 user, load average: 0.00, 0.01, 0.05

ps

Snapshot of current processes.

# 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

Dynamic view of processes sorted by CPU usage.

# top

kill

Terminate a process by PID.

kill 956
kill -9 7291

11. Managing Processes

Process states: R (running), S (sleeping), D (uninterruptible), Z (zombie), T (stopped).

Foreground & Background

Append & to run a command in the background. cp name.csv name-copy.csv & Use bg to resume a stopped background job, fg to bring it to the foreground, jobs to list jobs, and nohup to keep a job running after logout.

12. Daemons

Daemons run in the background with PID 1 as parent (e.g., systemd, httpd).

systemctl commands:

systemctl start nginx
systemctl stop nginx
systemctl restart nginx
systemctl status nginx
systemctl enable nginx
systemctl disable nginx
systemctl is-enabled nginx
systemctl list-unit-files --type=service

13. File Compression and Extraction

Archive with tar, compress with gzip or bzip2.

tar -cvf archive.tar files/
gzip archive.tar   # creates archive.tar.gz
gzip -d archive.tar.gz
tar -zcvf archive.tar.gz files/
tar -zxvf archive.tar.gz

View compressed files without extracting:

zcat archive.tar.gz
zless archive.tar.gz
zmore archive.tar.gz

ZIP format (common on Windows):

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

14. Compiling and Installing Software

When a package is not in the repository, compile from source.

Download source code.

Extract archive.

Run ./configure to check dependencies.

Run make to compile.

Run make install to install.

Example installing htop:

scp htop-3.0.0.tar.gz root@host:.
 tar -zxvf htop-3.0.0.tar.gz
 cd htop-3.0.0
 ./configure
 make
 sudo make install

15. Networking

ifconfig

Shows network interfaces; install with yum install net-tools if missing.

# ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> ...
lo: flags=73<UP,LOOPBACK,RUNNING> ...

host

Resolve hostnames to IPs and vice versa; install with yum install bind-utils.

# host github.com
github.com has address 13.229.188.59

ssh

Secure remote login.

ssh [email protected]   # default port 22
ssh -p 2222 user@host

Configure per‑user ~/.ssh/config for shortcuts:

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

Enable key‑based (password‑less) login:

ssh-keygen   # creates id_rsa and id_rsa.pub
ssh-copy-id root@host   # copies public key to server

wget

Download files from the command line.

wget http://example.com/file.zip
wget -c http://example.com/large.iso   # continue interrupted download

16. Backup

scp

Secure copy over SSH.

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

rsync

Efficient remote synchronization (incremental backup).

yum install rsync
rsync -arv Images/ backups/
rsync -arv Images/ [email protected]:backups/
rsync -arv --delete Images/ backups/

17. System Control

Shutdown, reboot, or power off the system.

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

Summary

After reading this guide, you should have a comprehensive understanding of Linux fundamentals and practical command‑line skills.

Give it a 👍 if you found it helpful.

Source: https://juejin.cn/post/6938385978004340744