Table of Contents

1. Linux Version
2. Files & Directories Permission
3. SUID & SGID
4. Services & Processes
5. Network Configuration
6. Linux Password

Linux is a versatile operating system available in numerous distributions ("distros") that are customized for different uses. Unlike proprietary alternatives, Linux manages computer hardware resources while allowing various software applications to communicate with the underlying components.

Components

Linux consists of various interrelated components that together create a functional operating system environment.

Component	Description
Bootloader	Code that initiates the operating system startup, such GRUB.
OS Kernel	Core component managing hardware resources and I/O operations
Daemons	Background services ensuring key functions like scheduling and printing work properly
OS Shell	Command-line interface (CLI) between user and system (common shells: Bash, Zsh, Fish)
Graphics server	"X" or "X-server" subsystem that enables graphical applications to run
Window Manager	Graphical interface (GUI) like GNOME or KDE providing desktop environment with file browsers
Utilities	Programs performing specific functions for users or other applications

Linux Architecture

The Linux operating system can be broken down into layers:

Layer	Description
Hardware	Physical components (RAM, CPU, storage devices)
Kernel	Core system that virtualizes and controls hardware resources, preventing conflicts between processes
Shell	Command-line interface (CLI) for executing kernel functions via user commands
System Utility	Programs that perform specific maintenance or configuration tasks

File System Hierarchy

The Linux operating system follows a tree-like structure documented in the Filesystem Hierarchy Standard (FHS), organizing system resources into standardized top-level directories that create a consistent arrangement across distributions.

graph TD
    root["/"] --> bin["/bin"]
    root --> boot["/boot"]
    root --> dev["/dev"]
    root --> etc["/etc"]
    root --> home["/home"]
    root --> lib["/lib"]
    root --> media["/media"]
    root --> mnt["/mnt"]
    root --> opt["/opt"]
    root --> proc["/proc"]
    root --> root_dir["/root"]
    root --> run["/run"]
    root --> sbin["/sbin"]
    root --> sys["/sys"]
    root --> tmp["/tmp"]
    root --> usr["/usr"]
    root --> var["/var"]

Path	Description
/	Root filesystem containing files needed to boot the OS
/bin	Essential command binaries
/boot	Bootloader, kernel, and boot files
/dev	Device files for hardware access
/etc	System and application configuration files
/home	User home directories
/lib	Shared libraries needed for system boot
/media	Mount point for removable media
/mnt	Temporary mount point for filesystems
/opt	Optional third-party applications
/root	Home directory for the root user
/sbin	System administration binaries
/tmp	Temporary files (cleared on boot)
/usr	User programs, libraries and documentation
/var	Variable data (logs, emails, web files)

Linux Version

# Get linux version - works on most distributions
cat /etc/*-release
 
# Get linux version - kernel version only
uname -r
 
# Get linux version - full kernel information
uname -a
 
# Get linux version - detailed hardware and OS info
hostnamectl

Files & Directories Permission

SUID & SGID

Special permission bits that temporarily elevate privileges. SUID allows users to run programs with the file owner’s permissions, while SGID runs with the file’s group permissions. These enable administrators to grant limited elevated access for specific applications without giving users permanent higher privileges.

# Find SUID files
find / -perm -4000 -type f -exec ls -l {} \; 2>/dev/null
# OR using symbolic notation
find / -perm -u=s -type f -exec ls -l {} \; 2>/dev/null
 
# Find SGID files
find / -perm -2000 -type f -exec ls -l {} \; 2>/dev/null
# OR using symbolic notation
find / -perm -g=s -type f -exec ls -l {} \; 2>/dev/null

Services & Processes

Network Configuration

Linux Password