basic linux commands
basic linux commands
Essential Command Line Reference
muntaha Ghafoor
Table of Content:
2-Navigating the file systems: 2
3-File and directory operations: 3
4-Viewing and editing file content: 3
5-System Information Commands: 4
6-File permissions and ownership: 4
10-Searching for Files and Content: 6
12-Understanding File Permissions: 7
14-System Information Commands: 8
Introduction:
The command line, also known as the Shell or terminal. The command line interface (CLI) is the heart of Linux. While graphical interfaces exist, the true power of Linux lies in its terminal. A text-based interface where users interact directly with the operating system by typing commands. Mastering basic Linux commands is the first and most important step in becoming proficient with Linux, whether for system administration, software development, or cybersecurity.
Navigating the file systems:
Linux organizes files and directories in a hierarchical tree structure starting from the root directory, represented by a forward slash (/). These commands are used to move around and understand this structure such as:
$ pwd
The pwd (Print Working Directory) command displays the full path of the current directory. This is essential for understanding where you are in the file system at any given time.
$ ls -la
The ls command lists files and directories. The -l flag provides detailed listing including permissions, owner, size, and modification date. The -a flag shows hidden files (files beginning with a dot). Combining these as -la gives a comprehensive view of all files in a directory.
$ cd /home/user/Documents
The cd (Change Directory) command moves to a specified directory. Using cd .. moves up one level, cd ~ returns to the home directory, and cd – returns to the previous directory.
| Command | Description | Example |
| Pwd | Prints the current working directory | pwd |
| ls | Lists files and directories | ls -la |
| cd | Changes the current directory | Cd /home/user |
| tree | Displays directory structure as a tree | tree / etc |
File and directory operations:
Creating, copying, moving and deleting files and directories are most important and common tasks performed in the terminal. These commands are the backbone of daily Linux usage.
| Command | Description | Example |
| touch | Creates an empty file | touch notes.txt |
| mkdir | Creates a new directory | mkdir project |
| cp | Copies files or directories | cp file.txt backup.txt |
| mv | Moves or rename files | mv old.txt new.tct |
| rm | Deletes files | rm file.txt |
| rm -rf | Deletes directories recursively | rm -rf folder/ |
| rmdir | Removes an empty directory | rmdir empty_folder |
Be careful when use rm command, particularly rm -rf, since linux does not have built-in recycle bin for terminal deletions.
Viewing and editing file content:
Linux provides multiple commands for viewing file contents, each suited to different situations depending on the file size and the user’s needs.
$ cat /etc/passwd
The cat (concatenate) command displays the entire content of a file at once. It is best suited for small files. For larger files, it can be overwhelming as it outputs everything at once.
$ less /var/log/syslog
The less command provides a paginated view of file contents, allowing users to scroll up and down through large files. Press q to quit, / to search, and n to find the next match.
$ head -20 file.txt
$ tail -20 file.txt
The head command shows the first N lines of a file (default 10), while tail shows the last N lines. The tail -f command is particularly useful for monitoring log files in real time as it continuously displays new lines as they are added.
System Information Commands:
Understanding the state of a Linux system requires commands that can report on processes, memory, disk usage, and system resources.
| Command | Description |
| uname -a | Display all system information including kernel version |
| whoami | Show current logged-in username |
| id | Show user ID and group memberships |
| df -h | Show disk space usage in human-readable format |
| free -h | Show memory usage in human-readable format |
| top | Interactive process viewer showing CPU and memory usage |
| ps aux | List all running processes with details |
| uptime | Show how long the system has been running |
File permissions and ownership:
Linux has a robust permission system that controls who can read, write, or execute files. Understanding and managing permissions is critical for system security.
$ chmod 755 script.sh
The chmod command changes file permissions. Permissions are represented as three octet values for owner, group, and others. The value 7 (rwx) gives full permissions, 5 (r-x) gives read and execute, and 4 (r–) gives read only.
$ chown muntaha:users file.txt
The chown command changes file ownership. The format is chown user:group filename. This is essential for managing who has access to specific files and directories.
$ sudo command
The sudo (superuser do) command allows permitted users to run commands with elevated privileges. It is safer than logging in as root because it creates an audit trail and requires authentication.
Viewing file content:
| commands | Description |
| cat file.txt | Reads and displays file content / print entire file |
| less file.txt | Scroll through file |
| head file.txt | Show first 10 lines |
| tail file.txt | Show last 10 lines |
| tail -f file.txt | Live file monitering |
Text Editors:
| Editor | Commands | Best for |
| nano | Nano file.txt | Beginners |
| vim | Vim file.txt | Advanced users |
| Gedit | Gedit file.txt | GUI editor |
Nano shortcuts:
Ctrl+o = save
Ctrl+x = Exit
Ctrl+k = Cut line
Networking Commands:
| Commands | Example | Description |
| ifconfig | ifcofig | Shows your ip and network info |
| ip a | ip a | Modern version of ifconfig |
| ping | ping google.com | Test connection to a host |
| netstat | netstat -an | Shows active network connections |
| curl | curl <url> | Fetches data from a URL |
| wget | wget <url> | Downloads a file from internet |
| Ssh | ssh user@192.168.1.1 | Connect to remote machine |
| Traceroute | traceroute google.com | Shows path packets take to reach host |
Searching for Files and Content:
Locating specific files or text within files is a frequent task, particularly during troubleshooting or security investigations.
| Command | Description | Example |
| find | Searches for files based on criteria | find / -name “*.log” |
| grep | Searches for text patterns within files | grep “error” log.txt |
| locate | Quickly finds files using a prebuilt index | locate passwd |
| which | Shows the location of a command’s executable | which python3 |
The grep command is one of the most heavily used tools in Linux, especially in cybersecurity contexts, where it is often used to search log files for suspicious activity, filter command output, or scan scripts for specific patterns.
Disk Usage Connands:
| Commands | Description |
| df -h | Show total disk space |
| du -sh folder | Show size of a folder |
| lsblk | List disks & partitions |
| fdisk -l | Detailed disk info (sudo) |
Understanding File Permissions:
Every file has 3 permission sets
Owner, Group, others
3 types
Read(r), write(w), Execute(x)
Example:
-rwxr – xr–
Owner rwx (full access)
Group r -x (read+execute)
Others r– (read only)
Archiving with tar:
| Commands | Description |
| tar -cvf file.tar folder | Create archive |
| tar -xvf file.tar | Extract archive |
| tar -czvf file.tar.gz folder | Create compressed archive |
| tar -xzvf file.tar.gz | Extract compressed archive |
System Information Commands:
Understanding system status and resource usage is essential for administration and troubleshooting.
| Command | Description | Example |
| uname -a | Displays system and kernel information | uname -a |
| top / htop | Shows real-time running processes and resource usage | top |
| df -h | Displays disk space usage in human-readable form | df -h |
| du -sh | Shows the size of a directory | du -sh /var/log |
| ps aux | Lists all currently running processes | ps aux |
| whoami | Displays the current logged-in user | whoami |
Getting Help:
Nearly every Linux command includes built-in documentation accessible directly from the terminal:
- man <command>: Opens the manual page for a command, providing a full description of its options and usage.
- <command> –help: Displays a brief summary of a command’s usage and available flags.
Conclusion:
Mastery of basic Linux commands forms the foundation for nearly every advanced skill in system administration, DevOps, and cybersecurity. Commands for navigating the filesystem, managing files, controlling permissions, searching content, and monitoring system resources are used constantly in real-world environments. Building fluency with these tools not only increases efficiency but also becomes essential when working with the remote servers and security tools commonly encountered in professional practice.