Linux Commands List - Danh sách lệnh cơ bản trong Linux - Linux cheat sheet

Linux Commands cheat sheet

Dưới đây là danh sách các lệnh cơ bản thường dùng trong hệ điều hành Linux, được phân loại theo chức năng để bạn dễ dàng tham khảo:

MAN: dùng để xem hướng dẫn sử dụng 1 lênh khác

man ls

## xem hướng dẫn sử dụng lệnh ls

Help: gọi hướng dẫn sử dụng lênh đơn giản

rm –help

Keyboard Shortcuts

TAB TAB: hiển thị thông tin còn thiếu về từ nào đó được nhập vào cmd.

CTRL + L: xoá dòng hiện tại.

CTRL + D: đóng terminal.

CTRL + U: cut dòng hiện tại.

CTRL + A: chuyển con trỏ tới đầu dòng.

Ctrl + E: chuyển con trỏ tới cuối dòng.

CTRL + C: dừng chạy lệnh.

CTRL + Z: chế độ sleep.

CTRL + ALT + T: mở mới terminal.

Lịch sử lệnh:

history: hiển thị lịch sử gõ lệnh cmd.
history -d 100: xoá 100 dòng trong lịch sử lệnh.
history -c: xoá hết lịch sử lệnh.
echo $HISTFILESIZE: in ra số lệnh được lưu trong history file.
echo $HISTSIZE: in ra số lệnh được lưu trong history memory.
!!: về lệnh trước đó.
!20: chạy 20 lệnh trước đó.
!-10: Run the last nth command.
!abc: chạy lệnh trước đó có bắt đầu là abc.
!abc:p: danh sách lệnh trước đó với bắt đầu là abc.
CTRL + R: Reverse search through history.
HISTTIMEFORMAT=”%d/%m/%y %T “: Record date/time of each command (add to ~/.bashrc for persistence).

Root Access (sudo, su)

sudo command: chạy lệnh với quyền root (for users in sudo or wheel group).
sudo su: chuyển quyền root.
sudo passwd root: đặt root password.
passwd username: đổi pass user’s password.
su: Become root (if root has a password).

Linux Paths

Paths:

Absolute: Starts with /
Relative: Relative to the current location
.: đường dẫn hiện tại
..: đường dẫn cha của đường dẫn hiện tại
~: đường dẫn home của user hiện tại

Thay đổi đường dẫn:

cd: về thư mục home của user
cd ~: thư mục home của user
cd -: đường dẫn cuối cùng
cd /path_to_dir: vào đường dẫn được chỉ định
pwd: in ra đường dẫn hiện tại

Cài đặt

sudo apt install tree: cài đặt tree app

ls Command: hiển thị danh sách có trong thư mục

Usage: ls [OPTIONS] [FILES]

-l: Long listing
-a: All files (including hidden)
-1: Single column
-d: Directory information
-h: Human-readable sizes
-S: Sort by size
-X: Sort by extension
–hide: Hide specific files
-R: Recursive listing
-i: Inode number

Disk Usage

du -sh ~: kích thước/dung lượng đường dẫn

File Timestamps and Date

ls -lu: Access time (atime)
ls -l, ls -lt: Modification time (mtime)
ls -lc: Change time (ctime)
stat file.txt: All timestamps
ls -l –full-time /etc/: Full timestamps

Modifying Timestamps with Touch

touch file.txt: Create or update timestamps
touch -a file, touch -m file: Modify atime or mtime
touch -m -t 201812301530.45 a.txt: Specific date/time
touch -d “2010-10-31 15:45:30” a.txt: Both atime and mtime
touch a.txt -r b.txt: Copy timestamps

Date and Calendar

date: Current date/time
cal, cal 2021, cal 7 2021: Calendars
cal -3: Previous, current, next month
date –set=”2 OCT 2020 18:00:00″: Set date/time

Sorting with ls

ls -l: Sorted by name
ls -lt: Sorted by mtime, newest first
ls -ltu: Sorted by atime
ls -ltu –reverse: Reverse order

Viewing Files (cat, less, more, head, tail, watch)

Displaying File Contents

cat filename: Display content
cat -n filename: Line numbers
cat filename1 filename2 > filename3: Concatenate

Tail and Head

tail filename: Last 10 lines
tail -n 15 filename: Last 15 lines
tail -n +5 filename: Starting with line 5
tail -f filename: Real-time updates
head filename: First 10 lines
head -n 15 filename: First 15 lines

Monitoring Commands

watch -n 3 ls -l: Refresh every 3 seconds

Working with Files and Directories

Creating and Updating Files

touch filename: Create a new file or update timestamps.

Creating Directories

mkdir dir1: Create a new directory.
mkdir -p mydir1/mydir2/mydir3: Create nested directories.

cp Command: Copy files and directories:

cp file1 file2: Copy file1 to file2.
cp file1 dir1/file2: Copy to another directory with a different name.
cp -i file1 file2: Prompt before overwrite.
cp -p file1 file2: Preserve permissions.
cp -v file1 file2: Verbose output.
cp -r dir1 dir2/: Recursively copy directories.
cp -r file1 file2 dir1 dir2 dest_dir/: Copy multiple items to a destination.

mv Command: Move or rename files and directories:

mv file1 file2: Rename a file.
mv file1 dir1/: Move to a directory.
mv -i file1 dir1/: Prompt before overwrite.
mv -n file1 dir1/: Prevent overwriting.
mv -u file1 dir1/: Update based on modification time.
mv file1 dir1/file2: Move and rename.
mv file1 file2 dir1/ dir2/ dest_dir/: Move multiple items.

rm Command: Remove files and directories:

rm file1: Remove a file.
rm -v file1: Verbose removal.
rm -r dir1/: Remove a directory.
rm -rf dir1/: Force removal without prompt.
rm -ri file1 dir1/: Prompt for each removal.

Secure File Deletion

shred -vu -n 100 file1: Securely overwrite and remove a file.

Piping and Command Redirection

Piping Examples

ls -lSh /etc/ | head: View the top 10 largest files.
ps -ef | grep sshd: Check if sshd is running.
ps aux –sort=-%mem | head -n 3: Top 3 processes by memory.

Command Redirection – điều hướng thông tin vào file

Redirect output and errors:

ps aux > processes.txt: Output to a file. Kết quả lệnh ps aux sẽ được ghi vào file .txt
id >> users.txt: Append output. Thêm nội dung vào cuối file hiện tại với >>
tail -n 10 /var/log/*.log > output.txt 2> errors.txt: Separate output and errors.
tail -n 2 /etc/passwd /etc/shadow > all.txt 2>&1: Redirect all to one file.
cat /var/log/auth.log | grep “fail” | wc -l: Count occurrences.

Finding Files with locate and find

locate

sudo apt install plocate: Install plocate.
sudo updatedb: Update the database.
locate filename: Find a file by name.
locate -i filename: Case insensitive search.
locate -b ‘\filename’: Exact name search.
locate -r ‘regex’: Regular expression search.
locate -e filename: Check file existence.
which command: Show command path.

find: Search with various options:

find ~ -type f -size +1M: Files over 1MB.
Options include -type, -name, -iname, -size, -perm, -links, -atime, -amin, -mtime, -ctime, -user, and -group.

Searching for Text Patterns with grep

Usage: grep [OPTIONS] PATTERN FILE

Options

-n: Print line number.
-i: Case insensitive.
-v: Invert match.
-w: Match whole words.
-a: Include binary files.
-R: Recursive search.
-c: Count matches.
-C n: Context display (n lines around the match).

Extracting ASCII Characters from Binary Files

strings binary_file: Example strings /bin/ls.

VIM – Text Editor

Modes

Command Mode: Default on entry.
Insert Mode: Editing text.
Last Line Mode: Save/exit commands.

Config File

VIM settings: ~/.vimrc.

Commands

i, I, a, A, o: Enter Insert Mode.
:w!, :q!, :wq!, :e!: Save/quit commands in Last Line Mode.
x, dd, ZZ, u, G, $, 0, ^: Editing commands in Command Mode.
/string, ?string, n, N: Search commands in Command Mode.
vim -o file1 file2: Open files in stacked windows.
vim -d file1 file2: Highlight differences.

Navigation

Ctrl+w: Switch between files.

Account Management

## Account Management

/etc/passwd # users and info:

/etc/shadow # users’ passwords

/etc/group # groups

## User Commands

useradd [OPTIONS] username # Create user.

usermod [OPTIONS] username # Modify user.

userdel -r username # Delete user.

## Group Commands

groupadd group_name # Create group.

groupdel group_name # Delete group.

## Examples

useradd -m -d /home/john -c “C++ Developer” -s /bin/bash -G sudo,adm,mail john # Example of creating a user.

usermod -aG developers,managers john # Example of modifying a user.

Monitoring Users

## Commands

who -H # User info.

id # User info.

whoami # User info.

w # System usage.

uptime # System usage.

last # Login history.

last -u username # Login history for a specific user.

File Permissions

Understanding Permissions

Legend: u (user), g (group), o (others), a (all), r (read), w (write), x (execute), – (no access).

Displaying Permissions

ls -l /etc/passwd: View file permissions.
stat /etc/shadow: Detailed permission stats.

Changing Permissions

chmod u+r filename: Add read to user.
chmod u+r,g-wx,o-rwx filename: Adjust multiple permissions.
chmod ug+rwx,o-wx filename: Set multiple permissions.
chmod ugo+x filename: Add execute to all.
chmod a+r,a-wx filename: Modify all permissions.

Absolute Mode

chmod 777 filename: Set all permissions for all.
chmod 755 filename: Read & execute for group and others.
chmod 644 filename: Read-only for group and others.

Special Permissions

SUID: chmod u+s executable_file.
SGID: chmod g+s projects/.
Sticky Bit: chmod o+t temp/.

UMASK

Display: umask.
Set new value: umask new_value.

Ownership

Owner: chown new_owner file.
Group: chgrp new_group file.
Both: chown new_owner:new_group file.
Recursive: chown -R new_owner file.

File Attributes

Display: lsattr filename.
Change: chattr +-attribute filename.

Processes

Process Viewing

type rm: Check if rm is built-in or executable.
ps: Processes in current terminal.
ps -ef, ps aux, ps aux | less: System processes.
ps aux –sort=%mem | less: Sort by memory usage.
ps -ef –forest: ASCII process tree.
ps -f -u username: Processes by user.
pgrep -l sshd, pgrep -f sshd, ps -ef | grep sshd: Check for sshd.
pstree, pstree -c: Hierarchical process tree.

Dynamic Real-Time View

top: Start system monitor.
top shortcuts: h for help, space for refresh, d for delay, etc.
top -d 1 -n 3 -b > top_processes.txt: Top in batch mode.
Install htop for an interactive view.

Killing Processes

kill -l: List signals.
kill pid, kill -SIGNAL pid1 pid2 …: Send signals.
kill -2 pid, kill -HUP pid: Send specific signal.
pkill process_name, killall process_name: Kill by name.
kill $(pidof process_name): Kill using pidof.

Background and Foreground Management

command &: Run in background.
jobs: List jobs.
Ctrl + Z: Stop process.
fg %job_id: Resume in foreground.
bg %job_id: Resume in background.
nohup command &: Immune to hangups.

Networking

Getting Network Interface Information

ifconfig: Enabled interfaces.
ifconfig -a, ip address show: All interfaces.
ifconfig enp0s3, ip addr show dev enp0s3: Specific interface.
ip -4 address: Only IPv4 info.
ip -6 address: Only IPv6 info.
ip link show, ip link show dev enp0s3: L2 info, including MAC.
route, route -n, ip route show: Default gateway.
systemd-resolve –status: DNS servers.

Setting Network Interfaces

ifconfig enp0s3 down, ip link set enp0s3 down: Disable interface.
ifconfig enp0s3 up, ip link set enp0s3 up: Enable interface.
ifconfig -a, ip link show dev enp0s3: Check status.
ifconfig enp0s3 192.168.0.222/24 up, ip address add 192.168.0.112/24 dev enp0s3: Set IP.
ifconfig enp0s3:1 10.0.0.1/24: Secondary IP.
route del default gw, ip route del default, ip route add default via: Default gateway.
ifconfig enp0s3 hw ether, ip link set dev enp0s3 address: Change MAC.

Netplan for Static Network Configuration on Ubuntu

Stop/Disable NetworkManager.
Create/Modify YAML in /etc/netplan.
Apply config: sudo netplan apply.
Verify: ifconfig, route -n.

OpenSSH Configuration and Management

Installation

Ubuntu

sudo apt update && sudo apt install openssh-server openssh-client

CentOS

sudo dnf install openssh-server openssh-clients

Server Connection

ssh -p 22 username@server_ip # Connect using default SSH port

ssh -p 22 -l username server_ip # Connect with a specific username

ssh -v -p 22 username@server_ip # Connect in verbose mode for detailed information

# Ubuntu

sudo systemctl status ssh # Check SSH status

sudo systemctl stop ssh # Stop SSH service

sudo systemctl restart ssh # Restart SSH service

sudo systemctl enable ssh # Enable SSH to start on boot

sudo systemctl is-enabled ssh # Check if SSH is enabled on boot

# CentOS

sudo systemctl status sshd # Check SSH status

sudo systemctl stop sshd # Stop SSH service

sudo systemctl restart sshd # Restart SSH service

sudo systemctl enable sshd # Enable SSH to start on boot

sudo systemctl is-enabled sshd # Check if SSH is enabled on boot

Security Configuration

Edit /etc/ssh/sshd_config and then apply changes by restarting SSH:

Change port: Port 2278
Disable root login: PermitRootLogin no
Restrict user access: AllowUsers user1 user2
Configure firewall to filter SSH access
Enable Public Key Authentication, disable password-based login
Use SSH Protocol 2 only
Set client session intervals and max attempts for security

Remember to consult the man page (man sshd_config) for detailed configuration options.

File Transfer Techniques with SCP and RSYNC

SCP Usage

# Copy local file to remote host

scp a.txt john@80.0.0.1:~

scp -P 2288 a.txt john@80.0.0.1:~ # Custom port

# Copy from remote to local

scp -P 2290 john@80.0.0.1:~/a.txt .

# Copy entire directory to remote

scp -P 2290 -r projects/ john@80.0.0.1:~

RSYNC Commands

# Sync local directory to local backup

sudo rsync -av /etc/ ~/etc-backup/

# Mirror directory, deleting extraneous files from dest

sudo rsync -av –delete /etc/ ~/etc-backup/

# Exclude files during sync

rsync -av –exclude-from=’~/exclude.txt’ /source/ /dest/

# Sync over SSH with custom port

sudo rsync -av -e ‘ssh -p 2267’ /etc/ student@192.168.0.108:~/etc-backup/

Exclude Patterns Example

# exclude.txt could include patterns like:

*.avi

music/

abc.mkv

# Exclude specific file types during transfer

rsync -av –exclude=’*.mkv’ /source/ /dest/

WGET for File Download

# Install wget

sudo apt install wget # Ubuntu

sudo dnf install wget # CentOS

# Basic file download

wget https://example.com/file.iso

# Resume incomplete download

wget -c https://example.com/file.iso

# Download with bandwidth limit

wget –limit-rate=100k https://example.com/file.iso

# Download multiple files

wget -i urls.txt # urls.txt contains list of URLs

# Recursive download for offline viewing of a website

wget -mkEpnp http://example.org

Use these commands to efficiently copy files and directories across systems and for downloading content from the internet, ensuring data synchronization and maintaining web accessibility.

NETSTAT and SS Usage

# Display all ports and connections

sudo netstat -tupan

sudo ss -tupan

# Check if port 80 is open

netstat -tupan | grep :80

LSOF Commands

# List open files

lsof

# Files opened by a specific user

lsof -u username

# Files opened by a specific command/process

lsof -c sshd

Open files for TCP ports in LISTEN state

lsof -iTCP -sTCP:LISTEN

lsof -iTCP -sTCP:LISTEN -nP

Use these commands to monitor network connections, check for open ports, and view files opened by users or processes, especially for security and troubleshooting.

Nmap Scanning Guide

# SYN Scan (root required)

nmap -sS 192.168.0.1

# TCP Connect Scan

nmap -sT 192.168.0.1

# Scan All Ports

nmap -p- 192.168.0.1

# Scan Specific Ports

nmap -p 20,22-100,443,1000-2000 192.168.0.1

# Service Version Detection

nmap -p 22,80 -sV 192.168.0.1

# Ping Scan Network

nmap -sP 192.168.0.0/24

# Skip Host Discovery

nmap -Pn 192.168.0.0/24

# Exclude Specific IP from Scan

nmap -sS 192.168.0.0/24 –exclude 192.168.0.10

# Output Scan to File

nmap -oN output.txt 192.168.0.1

# OS Detection

nmap -O 192.168.0.1

# Aggressive Scan

nmap -A 192.168.0.1

# Read Targets from File & Output to File without DNS Resolution

nmap -n -iL hosts.txt -p 80 -oN output.txt

Only scan your own networks and systems, or those you have explicit permission to test. Unauthorized scanning can be illegal.

Software Management with DPKG and APT

DPKG

View .deb file info: dpkg –info package.deb
Install from .deb: sudo dpkg -i package.deb
List installed programs: dpkg –get-selections or dpkg-query -l
Find by name: dpkg-query -l | grep ssh
List package files: dpkg -L openssh-server
Find owning package: dpkg -S /bin/ls
Remove package: sudo dpkg -r package
Purge package: sudo dpkg -P package

APT

Update index: sudo apt update
Install/update: sudo apt install apache2
List upgradable: sudo apt list –upgradable
Full upgrade: sudo apt full-upgrade
Remove: sudo apt remove package
Purge: sudo apt purge package
Auto remove dependencies: sudo apt autoremove
Clean cache: sudo apt clean
List all packages: sudo apt list
Search: sudo apt list | grep nginx
Show package info: sudo apt show nginx
List installed: sudo apt list –installed

Task Scheduling using Cron

crontab -e # Edit crontab

crontab -l # List tasks

crontab -r # Remove tasks

# Schedule Format:

* * * * * command # Every minute

15 * * * * command # Hourly

30 18 * * * command # Daily

3 22 * * 1 command # Weekly

10 6 1 * * command # Monthly

@yearly command # Yearly

@reboot command # At reboot

Getting System Hardware Information

General Hardware

lshw # Full hardware info

lshw -short # Short format

lshw -json # JSON format

lshw -html # HTML format

CPU Information

lscpu # CPU details

lshw -C cpu # Hardware-specific CPU details

lscpu -J # JSON format

Memory Information

dmidecode -t memory # RAM specs

dmidecode -t memory | grep -i size

dmidecode -t memory | grep -i max

free -m # Memory usage

PCI and USB Devices

lspci # PCI buses and connected devices

lspci | grep -i wireless

lspci | grep -i vga

lsusb # USB controllers and devices

lsusb -v # Verbose output

Storage Devices

lshw -short -C disk

fdisk -l # List disks

fdisk -l /dev/sda

lsblk # Block devices list

Network Devices

lshw -C network

iw list # Wi-Fi cards

iwconfig # Wi-Fi configuration

iwlist scan # Wi-Fi networks scan

System Information via /proc

cat /proc/cpuinfo # CPU info

cat /proc/meminfo # Memory info

cat /proc/version # System version

uname -r # Kernel version

uname -a # All system info

Battery Power

acpi -bi # Battery info

acpi -V # All ACPI info

Working with Device Files (dd)

# Backup MBR

dd if=/dev/sda of=~/mbr.dat bs=512 count=1

# Restore MBR

dd if=~/mbr.dat of=/dev/sda bs=512 count=1

# Clone partition

dd if=/dev/sda1 of=/dev/sdb2 bs=4M status=progress

Use these commands to check hardware specifications and perform operations with device files safely.

Service Management

# Analyze boot process

systemd-analyze

systemd-analyze blame

# List active units

systemctl list-units

systemctl list-units | grep ssh

# Service status

sudo systemctl status nginx.service

# Stop service

sudo systemctl stop nginx

# Start service

sudo systemctl start nginx

# Restart service

sudo systemctl restart nginx

# Reload service config

sudo systemctl reload nginx

sudo systemctl reload-or-restart nginx

# Enable service at boot

sudo systemctl enable nginx

# Disable service at boot

sudo systemctl disable nginx

# Check if service is enabled at boot

sudo systemctl is-enabled nginx

# Mask service

sudo systemctl mask nginx

# Unmask service

sudo systemctl unmask nginx

Ubuntu

sudo systemctl status ssh # Check SSH service status

sudo systemctl stop ssh # Stop SSH service

sudo systemctl restart ssh # Restart SSH service

sudo systemctl enable ssh # Enable SSH to start on boot

sudo systemctl is-enabled ssh # Check if SSH is enabled on boot

CentOS

sudo systemctl status sshd # Check SSHD service status

sudo systemctl stop sshd # Stop SSHD service

sudo systemctl restart sshd # Restart SSHD service

sudo systemctl enable sshd # Enable SSHD to start on boot

sudo systemctl is-enabled sshd # Check if SSHD is enabled on boot

Security Configuration

To configure security settings, edit /etc/ssh/sshd_config. Apply changes by restarting SSH. Key configurations include:

Change SSH port:
- Port 2278
Disable root login:
- PermitRootLogin no
Restrict user access to specified users only:
- AllowUsers user1 user2
Configure firewall to filter SSH access
Enable Public Key Authentication and disable password-based login
Use SSH Protocol 2 only
Set client session intervals and maximum attempts for increased security

Note: Consult the man page (man sshd_config) for detailed configuration options.

Bash Programming

Bash Aliases

alias # List all aliases

alias name=’command’ # Create an alias

unalias name # Remove an alias

Useful Aliases

alias c=’clear’

alias cl=’clear; ls; pwd’

alias root=’sudo su’

alias ports=’netstat -tupan’

alias sshconfig=’sudo vim /etc/ssh/sshd_config’

alias update=’sudo apt update && sudo apt dist-upgrade -y && sudo apt clean’

Interactive File Manipulation

alias cp=’cp -i’

alias mv=’mv -i’

alias rm=’rm -i’

Bash Variables

variable=”value” # Define a variable

echo $variable # Reference a variable

declare -r const=100 # Define a read-only variable

unset variable # Unset a variable

env | grep PATH # Find an environment variable

export PATH=$PATH:~/bin # Modify the PATH variable

Special Variables

$0, $1, $2, …, ${10} # Script name & positional arguments

$# # Number of positional arguments

“$*” # All positional arguments as a single string

$? # Exit status of the last command

Program Flow Control

if [ condition ]; then command; fi # Basic if statement

if [ condition ]; then command; else other_command; fi # If-else statement

if [ condition ]; then command; elif [ condition ]; then… # If-elif-else statement

Test Conditions

# Numeric comparisons: -eq, -ne, -lt, -le, -gt, -ge

# File checks: -s, -f, -d, -x, -w, -r

# String comparisons: =, !=, -n (not zero), -z (is zero)

# Logical operators: && (and), || (or)

Loops and Functions

for i in {1..5}; do echo “Loop $i”; done # For loop

while [ condition ]; do command; done # While loop

case “$variable” in pattern) command;; esac # Case statement

function name() { command; } # Function definition

name() { command; } # Alternative function syntax

name # Call a function

Command Examples

crontab -e # Edit crontab file

crontab -l # List crontab entries

crontab -r # Remove crontab entries

Combine these constructs to write effective bash scripts for task automation and system management.

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