Complete Linux CLI Navigation Guide for Beginners & Pros

Master Linux command line interface with this comprehensive guide covering navigation, file operations, permissions, and advanced CLI techniques.

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Linux Command Line Interface Navigation Guide

Table of Contents

1. [Introduction](#introduction) 2. [Terminal Basics](#terminal-basics) 3. [File System Structure](#file-system-structure) 4. [Essential Navigation Commands](#essential-navigation-commands) 5. [File and Directory Operations](#file-and-directory-operations) 6. [File Permissions and Ownership](#file-permissions-and-ownership) 7. [Text Processing Commands](#text-processing-commands) 8. [System Information Commands](#system-information-commands) 9. [Process Management](#process-management) 10. [Network Commands](#network-commands) 11. [Command Line Tips and Tricks](#command-line-tips-and-tricks) 12. [Advanced Features](#advanced-features)

Introduction

The Linux Command Line Interface (CLI) is a powerful text-based interface that allows users to interact with the operating system through commands. Unlike graphical user interfaces, the CLI provides direct access to system functions and offers greater control, automation capabilities, and efficiency for system administration and development tasks.

The CLI operates through a shell, which is a program that interprets and executes commands. The most common shell in Linux distributions is Bash (Bourne Again Shell), though other shells like Zsh, Fish, and Dash are also available.

Terminal Basics

Understanding the Shell Prompt

The shell prompt is the text displayed in the terminal that indicates the system is ready to accept commands. A typical prompt format looks like:

`bash username@hostname:current_directory$ `

| Component | Description | Example | |-----------|-------------|---------| | username | Current logged-in user | john | | hostname | Computer name | server01 | | current_directory | Present working directory | /home/john | | $ or # | User privilege indicator | $ (regular user), # (root) |

Terminal Shortcuts

| Shortcut | Action | |----------|--------| | Ctrl + C | Interrupt/cancel current command | | Ctrl + D | Exit terminal or end input | | Ctrl + L | Clear terminal screen | | Ctrl + A | Move cursor to beginning of line | | Ctrl + E | Move cursor to end of line | | Ctrl + U | Delete from cursor to beginning of line | | Ctrl + K | Delete from cursor to end of line | | Tab | Auto-complete commands and filenames | | Up/Down Arrow | Navigate command history |

File System Structure

Linux follows a hierarchical file system structure starting from the root directory (/). Understanding this structure is crucial for effective navigation.

Standard Directory Structure

| Directory | Purpose | Description | |-----------|---------|-------------| | / | Root directory | Top-level directory of the file system | | /bin | Essential binaries | Basic system commands available to all users | | /boot | Boot files | Files needed for system boot process | | /dev | Device files | Hardware device representations | | /etc | Configuration files | System-wide configuration files | | /home | User directories | Personal directories for regular users | | /lib | Libraries | Shared libraries needed by system programs | | /media | Removable media | Mount points for removable devices | | /mnt | Mount points | Temporary mount points for file systems | | /opt | Optional software | Third-party software packages | | /proc | Process information | Virtual file system with system information | | /root | Root user home | Home directory for root user | | /run | Runtime data | Runtime system information | | /sbin | System binaries | System administration commands | | /tmp | Temporary files | Temporary files deleted on reboot | | /usr | User programs | User applications and utilities | | /var | Variable data | Log files, databases, and other changing data |

Essential Navigation Commands

pwd - Print Working Directory

The pwd command displays the current directory path.

`bash pwd `

Output example: ` /home/username/documents `

Notes: - Always shows absolute path from root directory - Useful for confirming current location in file system - No options commonly used with this command

ls - List Directory Contents

The ls command lists files and directories in the current or specified directory.

Basic syntax: `bash ls [options] [directory] `

Common options:

| Option | Description | Example | |--------|-------------|---------| | -l | Long format listing | ls -l | | -a | Show hidden files | ls -a | | -h | Human readable sizes | ls -lh | | -t | Sort by modification time | ls -lt | | -r | Reverse order | ls -lr | | -R | Recursive listing | ls -R | | -d | List directories themselves | ls -ld /home |

Examples:

`bash

Basic listing

ls

Long format with hidden files

ls -la

Human readable sizes sorted by time

ls -lht

List specific directory

ls /etc

Recursive listing of subdirectories

ls -R /home/user/documents `

Sample output of ls -la: ` total 24 drwxr-xr-x 4 user user 4096 Nov 15 10:30 . drwxr-xr-x 12 user user 4096 Nov 15 09:15 .. -rw-r--r-- 1 user user 220 Nov 10 08:30 .bashrc drwxr-xr-x 2 user user 4096 Nov 15 10:30 documents -rw-r--r-- 1 user user 1024 Nov 15 10:25 file.txt `

cd - Change Directory

The cd command changes the current working directory.

Basic syntax: `bash cd [directory] `

Special directory references:

| Symbol | Meaning | Example | |--------|---------|---------| | . | Current directory | cd . | | .. | Parent directory | cd .. | | ~ | Home directory | cd ~ | | - | Previous directory | cd - | | / | Root directory | cd / |

Examples:

`bash

Change to home directory

cd ~ cd

Move to parent directory

cd ..

Move to specific directory

cd /etc/apache2

Return to previous directory

cd -

Move multiple levels up

cd ../../..

Change to subdirectory

cd documents/projects `

Notes: - Without arguments, cd returns to home directory - Supports both absolute and relative paths - Tab completion works with directory names - Use quotes for directories with spaces: cd "My Documents"

File and Directory Operations

mkdir - Create Directories

Creates new directories in the file system.

Basic syntax: `bash mkdir [options] directory_name `

Common options:

| Option | Description | Example | |--------|-------------|---------| | -p | Create parent directories | mkdir -p path/to/new/dir | | -m | Set permissions | mkdir -m 755 newdir | | -v | Verbose output | mkdir -v newdir |

Examples:

`bash

Create single directory

mkdir documents

Create multiple directories

mkdir dir1 dir2 dir3

Create nested directory structure

mkdir -p projects/web/html/css

Create with specific permissions

mkdir -m 755 public_folder

Verbose creation

mkdir -v new_project `

rmdir and rm - Remove Directories and Files

rmdir removes empty directories only:

`bash

Remove empty directory

rmdir empty_folder

Remove multiple empty directories

rmdir dir1 dir2 dir3 `

rm removes files and directories:

Basic syntax: `bash rm [options] file_or_directory `

Common options:

| Option | Description | Example | |--------|-------------|---------| | -r | Recursive (for directories) | rm -r directory | | -f | Force removal | rm -f file | | -i | Interactive confirmation | rm -i file | | -v | Verbose output | rm -v file |

Examples:

`bash

Remove single file

rm file.txt

Remove multiple files

rm file1.txt file2.txt file3.txt

Remove directory and contents

rm -r old_project

Force remove without confirmation

rm -rf temp_folder

Interactive removal

rm -i important_file.txt `

Warning: Be extremely careful with rm -rf as it permanently deletes files and directories without confirmation.

cp - Copy Files and Directories

Copies files and directories from source to destination.

Basic syntax: `bash cp [options] source destination `

Common options:

| Option | Description | Example | |--------|-------------|---------| | -r | Recursive copy | cp -r source_dir dest_dir | | -i | Interactive (prompt before overwrite) | cp -i file1 file2 | | -v | Verbose output | cp -v file1 file2 | | -p | Preserve attributes | cp -p file1 file2 | | -u | Update (copy only newer files) | cp -u file1 file2 |

Examples:

`bash

Copy single file

cp document.txt backup.txt

Copy file to different directory

cp report.pdf /home/user/documents/

Copy directory recursively

cp -r project_folder /backup/

Copy with preserved permissions

cp -p config.conf config.conf.backup

Copy multiple files to directory

cp file1.txt file2.txt file3.txt /destination/ `

mv - Move/Rename Files and Directories

Moves files and directories or renames them.

Basic syntax: `bash mv [options] source destination `

Examples:

`bash

Rename file

mv oldname.txt newname.txt

Move file to different directory

mv document.pdf /home/user/documents/

Move and rename simultaneously

mv old_report.txt /archive/final_report.txt

Move multiple files

mv file1.txt file2.txt file3.txt /destination/

Rename directory

mv old_folder_name new_folder_name `

File Permissions and Ownership

Understanding File Permissions

Linux uses a permission system to control access to files and directories. Permissions are displayed in the long format listing (ls -l).

Permission format: ` -rwxrwxrwx `

| Position | Meaning | |----------|---------| | 1st character | File type (- file, d directory, l link) | | 2-4 characters | Owner permissions | | 5-7 characters | Group permissions | | 8-10 characters | Other permissions |

Permission types:

| Symbol | Permission | Octal Value | |--------|------------|-------------| | r | Read | 4 | | w | Write | 2 | | x | Execute | 1 | | - | No permission | 0 |

chmod - Change File Permissions

Basic syntax: `bash chmod [options] permissions file/directory `

Octal notation examples:

| Octal | Binary | Permissions | Description | |-------|--------|-------------|-------------| | 755 | 111 101 101 | rwxr-xr-x | Owner: rwx, Group: r-x, Other: r-x | | 644 | 110 100 100 | rw-r--r-- | Owner: rw-, Group: r--, Other: r-- | | 600 | 110 000 000 | rw------- | Owner: rw-, Group: ---, Other: --- | | 777 | 111 111 111 | rwxrwxrwx | All permissions for everyone |

Examples:

`bash

Set specific permissions using octal

chmod 755 script.sh

Make file executable for owner

chmod u+x program.py

Remove write permission for group and others

chmod go-w sensitive_file.txt

Set read and write for owner, read only for others

chmod 644 document.txt

Recursive permission change

chmod -R 755 /var/www/html/ `

chown - Change File Ownership

Basic syntax: `bash chown [options] owner:group file/directory `

Examples:

`bash

Change owner only

chown newuser file.txt

Change owner and group

chown newuser:newgroup file.txt

Change group only

chown :newgroup file.txt

Recursive ownership change

chown -R apache:apache /var/www/html/ `

Text Processing Commands

cat - Display File Contents

Displays the entire content of files.

Basic syntax: `bash cat [options] file1 [file2 ...] `

Examples:

`bash

Display single file

cat document.txt

Display multiple files

cat file1.txt file2.txt

Number lines

cat -n document.txt

Show non-printing characters

cat -A document.txt `

less and more - Page Through Files

less (preferred) and more allow viewing large files page by page.

`bash

View file with less

less large_file.txt

View file with more

more large_file.txt `

Navigation keys in less:

| Key | Action | |-----|--------| | Space | Next page | | b | Previous page | | / | Search forward | | ? | Search backward | | n | Next search result | | N | Previous search result | | q | Quit |

head and tail - Display File Parts

head shows the beginning of files, tail shows the end.

Examples:

`bash

Show first 10 lines (default)

head file.txt

Show first 20 lines

head -n 20 file.txt

Show last 10 lines

tail file.txt

Show last 5 lines

tail -n 5 file.txt

Follow file changes (useful for logs)

tail -f /var/log/syslog `

grep - Search Text Patterns

Searches for patterns in files using regular expressions.

Basic syntax: `bash grep [options] pattern file(s) `

Common options:

| Option | Description | Example | |--------|-------------|---------| | -i | Ignore case | grep -i "error" log.txt | | -n | Show line numbers | grep -n "pattern" file.txt | | -r | Recursive search | grep -r "function" /code/ | | -v | Invert match | grep -v "debug" log.txt | | -c | Count matches | grep -c "error" log.txt |

Examples:

`bash

Simple pattern search

grep "error" system.log

Case insensitive search

grep -i "warning" *.log

Search with line numbers

grep -n "TODO" source.py

Recursive search in directory

grep -r "configuration" /etc/

Search for whole words

grep -w "test" file.txt

Multiple patterns

grep -E "error|warning|critical" system.log `

System Information Commands

System Status Commands

| Command | Description | Example | |---------|-------------|---------| | whoami | Current username | whoami | | id | User and group IDs | id | | uname | System information | uname -a | | hostname | System hostname | hostname | | uptime | System uptime | uptime | | date | Current date and time | date | | cal | Calendar | cal | | df | Disk space usage | df -h | | du | Directory space usage | du -sh /home | | free | Memory usage | free -h |

Detailed Command Examples

df - Disk Free Space: `bash

Human readable format

df -h

Show specific filesystem

df -h /home

Show inodes

df -i `

Sample output: ` Filesystem Size Used Avail Use% Mounted on /dev/sda1 20G 12G 7.2G 63% / /dev/sda2 100G 45G 50G 48% /home `

du - Disk Usage: `bash

Summary of current directory

du -sh .

Show subdirectory sizes

du -h --max-depth=1

Largest files and directories

du -ah | sort -rh | head -20 `

free - Memory Information: `bash

Human readable memory info

free -h

Show in megabytes

free -m `

Process Management

Process Viewing Commands

| Command | Description | Usage | |---------|-------------|-------| | ps | Show running processes | ps aux | | top | Real-time process viewer | top | | htop | Enhanced process viewer | htop | | pgrep | Find process IDs | pgrep firefox | | pidof | Find process IDs by name | pidof apache2 |

ps - Process Status

Common options:

`bash

Show all processes

ps aux

Show processes for current user

ps ux

Show process tree

ps auxf

Show specific processes

ps aux | grep apache `

Sample output: ` USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.1 225316 9012 ? Ss Nov14 0:02 /sbin/init user 1234 2.1 5.2 892456 85234 ? Sl 10:30 1:25 firefox `

Process Control

| Command | Description | Example | |---------|-------------|---------| | kill | Terminate process by PID | kill 1234 | | killall | Terminate process by name | killall firefox | | pkill | Kill processes by pattern | pkill -f "python script" | | nohup | Run command immune to hangups | nohup command & | | bg | Put job in background | bg %1 | | fg | Bring job to foreground | fg %1 | | jobs | List active jobs | jobs |

Kill signals:

| Signal | Number | Description | |--------|--------|-------------| | TERM | 15 | Graceful termination (default) | | KILL | 9 | Force kill | | HUP | 1 | Hang up | | INT | 2 | Interrupt (Ctrl+C) | | STOP | 19 | Stop process | | CONT | 18 | Continue process |

Examples:

`bash

Graceful termination

kill 1234

Force kill

kill -9 1234

Kill all instances

killall -9 firefox

Background process

command &

Start process immune to hangup

nohup long_running_script.sh & `

Network Commands

Network Information Commands

| Command | Description | Example | |---------|-------------|---------| | ping | Test network connectivity | ping google.com | | wget | Download files | wget http://example.com/file.zip | | curl | Transfer data from servers | curl -O http://example.com/file.txt | | ssh | Secure shell connection | ssh user@server.com | | scp | Secure copy over network | scp file.txt user@server:/path/ | | netstat | Network connections | netstat -tuln | | ss | Socket statistics | ss -tuln |

Examples:

`bash

Test connectivity

ping -c 4 google.com

Download file with wget

wget -O local_name.zip http://example.com/file.zip

HTTP request with curl

curl -X GET https://api.example.com/data

SSH connection

ssh -p 2222 user@192.168.1.100

Copy file to remote server

scp document.pdf user@server.com:/home/user/

Show listening ports

netstat -tuln | grep LISTEN `

Command Line Tips and Tricks

Command History

| Command | Description | |---------|-------------| | history | Show command history | | !! | Repeat last command | | !n | Repeat command number n | | !string | Repeat last command starting with string | | Ctrl+R | Search command history |

Command Chaining

| Operator | Description | Example | |----------|-------------|---------| | ; | Run commands sequentially | cmd1; cmd2; cmd3 | | && | Run next if previous succeeds | make && make install | | \|\| | Run next if previous fails | cmd1 \|\| cmd2 | | & | Run in background | long_command & | | \| | Pipe output to next command | ls -l \| grep txt |

Redirection

| Operator | Description | Example | |----------|-------------|---------| | > | Redirect output (overwrite) | ls > file_list.txt | | >> | Redirect output (append) | echo "text" >> file.txt | | < | Redirect input | sort < unsorted.txt | | 2> | Redirect errors | command 2> errors.txt | | &> | Redirect both output and errors | command &> all_output.txt |

Wildcards and Globbing

| Pattern | Description | Example | |---------|-------------|---------| | | Match any characters | ls .txt | | ? | Match single character | ls file?.txt | | [abc] | Match any of a, b, c | ls file[123].txt | | [a-z] | Match range | ls [a-m]*.txt | | {a,b,c} | Match alternatives | cp file.{txt,pdf} /backup/ |

Advanced Features

Environment Variables

Viewing and setting variables:

`bash

Show all environment variables

env

Show specific variable

echo $HOME echo $PATH

Set temporary variable

export MY_VAR="value"

Add to PATH

export PATH=$PATH:/new/path

Make permanent (add to ~/.bashrc)

echo 'export MY_VAR="value"' >> ~/.bashrc `

Important environment variables:

| Variable | Description | |----------|-------------| | HOME | User's home directory | | PATH | Executable search path | | USER | Current username | | SHELL | Current shell | | PWD | Present working directory | | EDITOR | Default text editor |

Command Substitution

Execute commands within other commands:

`bash

Using backticks (deprecated)

echo "Today is date"

Using $() (preferred)

echo "Today is $(date)"

Complex examples

files_count=$(ls | wc -l) echo "There are $files_count files"

Nested substitution

echo "Disk usage: $(df -h $(pwd) | tail -1 | awk '{print $5}')" `

Aliases

Create shortcuts for commonly used commands:

`bash

Create temporary alias

alias ll='ls -la' alias la='ls -A' alias l='ls -CF'

View current aliases

alias

Remove alias

unalias ll

Make permanent (add to ~/.bashrc)

echo "alias ll='ls -la'" >> ~/.bashrc `

Useful alias examples:

`bash alias ..='cd ..' alias ...='cd ../..' alias grep='grep --color=auto' alias mkdir='mkdir -pv' alias df='df -h' alias du='du -h' alias free='free -h' alias ps='ps auxf' alias ping='ping -c 5' alias cls='clear' `

Functions

Create reusable command sequences:

`bash

Simple function

mcd() { mkdir -p "$1" && cd "$1" }

Function with multiple commands

backup() { local source="$1" local dest="$HOME/backups/$(basename "$source")-$(date +%Y%m%d)" cp -r "$source" "$dest" echo "Backup created: $dest" }

Use functions

mcd new_project backup /important/directory `

This comprehensive guide covers the essential aspects of navigating and using the Linux command line interface. Regular practice with these commands and concepts will build proficiency and confidence in using the CLI effectively for system administration, development, and daily computing tasks.

Tags

  • CLI
  • Linux
  • bash
  • system-administration
  • terminal

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