Posted on Oct 15, 2024 • Edited on Oct 31, 2024

💻 Common Useful Linux Commands 🐧

Common Linux Commands and Descriptions

Linux FileSystem Structure

/ ├── bin/ # Essential user binaries (e.g., ls, cat), accessible by all users. ├── boot/ # Files needed to boot the system, like the kernel and bootloader configs. ├── dev/ # Device files representing hardware (e.g., /dev/sda for hard drives). ├── etc/ # System-wide configuration files (e.g., fstab, hosts). │ ├── init.d/ # Service scripts (start, stop, restart) │ ├── nginx/ # Configuration for the nginx web server │ └── ssh/ # SSH configuration files ├── home/ # User home directories for personal data. │ └── user/ # Directory for user 'user', ├── lib/ # Shared libraries essential for the system and kernel modules. ├── media/ # Mount points for removable media, external devices like USBs or DVDs. ├── mnt/ # Temporary mount directory ├── opt/ # Optional software packages or third-party apps. ├── proc/ # Process and kernel information ├── root/ # Home directory for root user ├── sbin/ # System binaries for administrative tasks (e.g., reboot, iptables). ├── tmp/ # Temporary files, often cleared on reboot. ├── usr/ # User programs and libraries, typically for installed packages. │ ├── bin/ # User commands │ ├── lib/ # User libraries │ └── share/ # Shared files └── var/ # Variable files (logs, databases, etc.) ├── log/ # Log files ├── cache/ # Application cache data └── tmp/ # Temporary files created by applications

File and Directory Operations

ls – Lists the contents of a directory.

ls ls -l # Long listing format ls -a # List all files, including hidden ones

cd – Changes the current directory.

cd /path/to/directory cd .. # Go up one directory cd ~ # Go to the home directory

mkdir – Creates a new directory.
```
mkdir new_directory 
```
rmdir – Removes an empty directory.
```
rmdir directory_name 
```

cp – Copies files or directories.

cp source_file destination cp -r source_directory destination_directory # Copy directories recursively

mv – Moves or renames files and directories.

mv old_name new_name mv file_name /path/to/destination/

rm – Removes files or directories.

rm file_name rm -r directory_name # Remove directories recursively

touch – Creates an empty file or updates the timestamp of an existing file.
```
touch file_name 
```

File Viewing & Manipulation

cat – Displays the contents of a file.
```
cat file_name 
```
less – Allows you to view file contents page by page.
```
less file_name 
```

head – Shows the first 10 lines of a file (default).

head file_name head -n 5 file_name # Show the first 5 lines

tail – Shows the last 10 lines of a file (default).

tail file_name tail -n 5 file_name # Show the last 5 lines

grep – Searches for patterns within files.

grep 'search_term' file_name grep -r 'search_term' /path/to/directory # Search recursively in directories

Permissions & Ownership

chmod – Changes file permissions.

chmod 755 file_name # Gives read, write, execute permissions to the owner and read, execute to others chmod +x script.sh # Make file executable

chown – Changes the file owner and group.
```
chown user:group file_name 
```

umask – Sets default file creation permissions.

umask 022 # Sets default permissions to 755 for directories and 644 for files

Process Management

ps – Displays the currently running processes.
```
ps ps aux # Show all processes 
```
top – Displays real-time system processes and resource usage.
```
top 
```

kill – Terminates a process by its PID.

kill process_id kill -9 process_id # Forcefully kill a process

htop – Interactive process viewer (requires installation).
```
htop 
```

System Information

df – Shows disk space usage.
```
df -h # Human-readable format 
```
du – Shows disk usage for files and directories.
```
du -h /path/to/directory 
```
free – Displays memory usage.
```
free -h # Human-readable format 
```
uname – Shows system information.
```
uname -a # Display all system info 
```
uptime – Shows how long the system has been running.
```
uptime 
```
whoami – Displays the current logged-in user.
```
whoami 
```
hostname – Displays or sets the system's hostname.
```
hostname 
```
lscpu – Displays CPU architecture information.
```
lscpu 
```

Network Commands

ping – Tests connectivity to a host.
```
ping google.com 
```
ifconfig – Displays network interface information (may require net-tools installation on some systems).
```
ifconfig 
```

ip – Configures network interfaces and routing.

ip addr show # Show IP addresses of network interfaces ip route show # Show routing table

curl – Fetches data from a URL.
```
curl https://example.com 
```
wget – Downloads files from the web.
```
wget https://example.com/file.zip 
```

Package Management

apt-get (for Debian/Ubuntu-based distributions) – Installs, updates, or removes software packages.

sudo apt-get update # Update package list sudo apt-get install package # Install a package sudo apt-get remove package # Remove a package

yum (for RedHat/CentOS-based distributions) – Installs, updates, or removes software packages.

sudo yum update # Update package list sudo yum install package # Install a package sudo yum remove package # Remove a package

File Compression

tar – Archives or extracts files.

tar -czvf archive_name.tar.gz /path/to/directory # Create a compressed archive tar -xzvf archive_name.tar.gz # Extract a compressed archive

zip – Compresses files into a zip archive.
```
zip archive_name.zip file1 file2 
```
unzip – Extracts a zip archive.
```
unzip archive_name.zip 
```

Miscellaneous

echo – Prints a message or variables to the terminal.
```
echo "Hello, World!" 
```
date – Displays or sets the system date and time.
```
date 
```

alias – Creates an alias for a command.

alias ll='ls -la' # Create a shortcut for 'ls -la'

history – Shows the command history.
```
history 
```
clear – Clears the terminal screen.
```
clear 
```

These are just a few of the many powerful commands in Linux, but they cover most of the common operations you'll perform daily.

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