📚 OS Concepts — Cooperative vs Preemptive Scheduling 🧵
Ever wondered how your computer decides who gets the CPU and when? Let’s break it down:
🔹 1. Cooperative Scheduling
🤝 The process gives up the CPU voluntarily
🛑 If it never gives up, no one else runs
⚠️ One buggy program = system freeze
🏗 Used in old Windows, embedded systems
🔹 2. Preemptive Scheduling (Non-Cooperative)
⏱️ OS uses a timer to interrupt running processes
🔁 CPU is forcefully switched between tasks
💪 More stable & fair
🏃 Used in Linux, Android, Windows, etc.
📌 Key Difference:
Cooperative: “I’ll tell you when I’m done”
Preemptive: “Time’s up! Next process please”
💡
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Ever wondered how your computer decides who gets the CPU and when? Let’s break it down:
🔹 1. Cooperative Scheduling
🤝 The process gives up the CPU voluntarily
🛑 If it never gives up, no one else runs
⚠️ One buggy program = system freeze
🏗 Used in old Windows, embedded systems
🔹 2. Preemptive Scheduling (Non-Cooperative)
⏱️ OS uses a timer to interrupt running processes
🔁 CPU is forcefully switched between tasks
💪 More stable & fair
🏃 Used in Linux, Android, Windows, etc.
📌 Key Difference:
Cooperative: “I’ll tell you when I’m done”
Preemptive: “Time’s up! Next process please”
💡
Modern OS = Preemptive, for fairness + safety!#OS #Scheduling #Preemptive #Cooperative #CSBasics #InfoSecTube
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🪡Internet Key Exchange (IKE) is a secure key management protocol that establishes secure, authenticated communication channels over IP networks. It's used to set up security associations (SAs) in Internet Protocol Security (IPsec) for VPN connections, ensuring both parties use common encryption and authentication methods for secure data exchange.
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🏛 3. EV – Extended Validation
Purpose: Maximum trust; strictest authentication.
✅ Validation Level: Very thorough business verification (legal, physical, operational existence)
📄 Certificate Info: Full organization details
👁 Browser Bar: Padlock + organization name in address bar (some browsers now hide this, but cert details still contain it)
💰 Cost: Most expensive
🧰 Use Case: Banks, e-commerce, government portals, high-trust sites
Example:
Address bar: 🔒 [Example Corp] https://example.com
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Purpose: Maximum trust; strictest authentication.
✅ Validation Level: Very thorough business verification (legal, physical, operational existence)
📄 Certificate Info: Full organization details
👁 Browser Bar: Padlock + organization name in address bar (some browsers now hide this, but cert details still contain it)
💰 Cost: Most expensive
🧰 Use Case: Banks, e-commerce, government portals, high-trust sites
Example:
Address bar: 🔒 [Example Corp] https://example.com
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A one-time pad is a cryptographic technique that ensures perfect secrecy, meaning it's mathematically impossible to decrypt a message without knowing the key. It works by using a random key of the same length as the message, encrypting each character or bit of the plaintext with the corresponding character or bit from the key using operations like XOR or modular addition. Crucially, the key is only used once and then discarded.
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📚 OS Concepts — Dining Philosophers Problem 🧵
Let’s solve a dinner table mystery that teaches us all about deadlock and resource sharing 👇
👨🎓 The Setup:
😱 The Problem:
If each picks up their left fork first, they all wait forever for the right fork
→ This causes a deadlock 💥
🔑 Solutions:
✅ Lock Ordering: Always pick lower-numbered fork first
✅ Asymmetric Strategy: Odd picks left-first, even picks right-first
✅ At Most 4 at Table: Prevents total deadlock
✅ Use a Waiter: Central manager checks availability
📌 Core Concepts:
Philosophers = Threads
Forks = Shared Resources
Eat = Critical Section
Think = Non-Critical Work
Deadlock, starvation, and concurrency — all on one dinner table!
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Let’s solve a dinner table mystery that teaches us all about deadlock and resource sharing 👇
👨🎓 The Setup:
5 philosophers sit around a table 🍽
5 forks placed between them 🍴
To eat, each needs 2 forks (left + right)
After eating → Think → Get hungry again
😱 The Problem:
If each picks up their left fork first, they all wait forever for the right fork
→ This causes a deadlock 💥
🔑 Solutions:
✅ Lock Ordering: Always pick lower-numbered fork first
✅ Asymmetric Strategy: Odd picks left-first, even picks right-first
✅ At Most 4 at Table: Prevents total deadlock
✅ Use a Waiter: Central manager checks availability
📌 Core Concepts:
Philosophers = Threads
Forks = Shared Resources
Eat = Critical Section
Think = Non-Critical Work
Deadlock, starvation, and concurrency — all on one dinner table!
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🚨 Replay Attack Explained 🔁
A replay attack is a sneaky cyber trick where attackers intercept legit data and resend it to fool systems into thinking it’s real — leading to unauthorized access or action manipulation.
🔍 How It Works:
1️⃣ Interception:
Attacker sniffs data between two parties (e.g. login or transaction).
2️⃣ Re-transmission:
They replay that data to the receiver, pretending to be the legit sender.
3️⃣ Deception:
The receiver gets tricked, thinking it’s valid — and boom 💥, the attacker is in!
📌 Examples:
🔓 Login Replay:
Stealing & reusing login credentials to access accounts.
💸 Transaction Replay:
Duplicating a payment to drain funds or cause confusion.
🛡 Session Replay:
Using stolen session tokens to impersonate users.
🧠 Stay safe! Use encryption, session expiration, and anti-replay mechanisms.
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A replay attack is a sneaky cyber trick where attackers intercept legit data and resend it to fool systems into thinking it’s real — leading to unauthorized access or action manipulation.
🔍 How It Works:
1️⃣ Interception:
Attacker sniffs data between two parties (e.g. login or transaction).
2️⃣ Re-transmission:
They replay that data to the receiver, pretending to be the legit sender.
3️⃣ Deception:
The receiver gets tricked, thinking it’s valid — and boom 💥, the attacker is in!
📌 Examples:
🔓 Login Replay:
Stealing & reusing login credentials to access accounts.
💸 Transaction Replay:
Duplicating a payment to drain funds or cause confusion.
🛡 Session Replay:
Using stolen session tokens to impersonate users.
🧠 Stay safe! Use encryption, session expiration, and anti-replay mechanisms.
#CyberSecurity #ReplayAttack #InfoSec #HackingExplained #CyberAwareness #StaySecure
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🔐 What is HOTP? (HMAC-based One-Time Password) 🔁
HOTP is a powerful algorithm used in multi-factor authentication (MFA) to boost your security beyond just passwords.
🧠 It works by generating one-time, unique passwords using:
🔑 A shared secret key
📈 A counter value (increases with each use)
Every time the counter updates, a new password is created — and it’s valid only once. Even if someone sees it, they can't reuse it! 🙅♂️
✅ Why Use HOTP?
🔸 Adds an extra layer of security
🔸 Prevents password reuse
🔸 Great for offline devices (no need for real-time clock)
💡 Used in hardware tokens, MFA apps, and enterprise systems.
#CyberSecurity #HOTP #MFA #OneTimePassword #Authentication #SecureAccess #InfoSec #IdentityVerification #2FA
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HOTP is a powerful algorithm used in multi-factor authentication (MFA) to boost your security beyond just passwords.
🧠 It works by generating one-time, unique passwords using:
🔑 A shared secret key
📈 A counter value (increases with each use)
Every time the counter updates, a new password is created — and it’s valid only once. Even if someone sees it, they can't reuse it! 🙅♂️
✅ Why Use HOTP?
🔸 Adds an extra layer of security
🔸 Prevents password reuse
🔸 Great for offline devices (no need for real-time clock)
💡 Used in hardware tokens, MFA apps, and enterprise systems.
#CyberSecurity #HOTP #MFA #OneTimePassword #Authentication #SecureAccess #InfoSec #IdentityVerification #2FA
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⛑Port mirroring, also known as SPAN (Switched Port Analyzer), is a networking technique where a network switch or router duplicates network packets from one port (the source port) and forwards them to another port (the destination or mirrored port). This allows network administrators to monitor and analyze traffic on a specific port without interrupting normal network operations.
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💻 4. IV – Individual Validation (for Code Signing)
Purpose: Authenticates individual developers for signing software/code.
✅ Validation Level: Verifies personal identity (via government ID, utility bills, etc.)
📄 Certificate Info: Includes individual's legal name
👁 Prompt: Shows developer’s name when users run signed software
💰 Cost: Varies
🧰 Use Case: Independent developers releasing apps or tools
Example (in a code-signing dialog):
"Publisher: John Doe"
Purpose: Authenticates individual developers for signing software/code.
✅ Validation Level: Verifies personal identity (via government ID, utility bills, etc.)
📄 Certificate Info: Includes individual's legal name
👁 Prompt: Shows developer’s name when users run signed software
💰 Cost: Varies
🧰 Use Case: Independent developers releasing apps or tools
Example (in a code-signing dialog):
"Publisher: John Doe"
📚 OS Concepts — When Do Kernel Modules Run? 🧵
Let’s break down how and when kernel module or device driver code executes!
🔧 A kernel module (like a device driver) is a piece of code that can be loaded/unloaded into the kernel at runtime. But when does it actually run?
✅ It runs when…
🔹 A device or syscall triggers a registered event
🔹 You load the module → insmod → runs init_module()
🔹 You unload the module → rmmod → runs cleanup_module()
🔹 A special file (like /dev/zero) is accessed → the corresponding driver’s function runs
🧠 Example:
Reading from /dev/zero calls the read handler of its device driver.
📌 Takeaway:
Drivers respond to events, they don’t idle or run endlessly!
#Kernel #DeviceDriver #OS
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Let’s break down how and when kernel module or device driver code executes!
🔧 A kernel module (like a device driver) is a piece of code that can be loaded/unloaded into the kernel at runtime. But when does it actually run?
✅ It runs when…
🔹 A device or syscall triggers a registered event
🔹 You load the module → insmod → runs init_module()
🔹 You unload the module → rmmod → runs cleanup_module()
🔹 A special file (like /dev/zero) is accessed → the corresponding driver’s function runs
🧠 Example:
Reading from /dev/zero calls the read handler of its device driver.
📌 Takeaway:
Drivers respond to events, they don’t idle or run endlessly!
#Kernel #DeviceDriver #OS
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🔄 Reflection Attack in Symmetric Protocols 🛡
A Reflection Attack is a clever trick used by attackers to exploit symmetric authentication protocols, especially when both parties use the same secret key. The attacker "reflects" a challenge back to the sender to bypass authentication without knowing the secret key.
⚙️ How It Works:
1️⃣ The attacker initiates a connection to the victim and receives a challenge (e.g. a nonce).
2️⃣ Instead of solving it, the attacker opens a second connection to the victim and sends the same challenge back.
3️⃣ The victim unknowingly solves their own challenge, thinking it's coming from a legit source.
4️⃣ The attacker grabs the valid response and uses it to authenticate in the original session. 😈
💥 Why It’s Dangerous:
Because the same protocol and key are used for both sides, there's no way to tell that the challenge came from the same party. It allows attackers to bypass authentication without breaking encryption.
🛑 Mitigation Tips:
✅ Use different keys or roles for client/server
✅ Add origin identifiers in challenges
✅ Employ asymmetric authentication if possible
#CyberSecurity #ReflectionAttack #SymmetricEncryption #NetworkSecurity #InfoSecTube #Hacking101 #StaySecure
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A Reflection Attack is a clever trick used by attackers to exploit symmetric authentication protocols, especially when both parties use the same secret key. The attacker "reflects" a challenge back to the sender to bypass authentication without knowing the secret key.
⚙️ How It Works:
1️⃣ The attacker initiates a connection to the victim and receives a challenge (e.g. a nonce).
2️⃣ Instead of solving it, the attacker opens a second connection to the victim and sends the same challenge back.
3️⃣ The victim unknowingly solves their own challenge, thinking it's coming from a legit source.
4️⃣ The attacker grabs the valid response and uses it to authenticate in the original session. 😈
💥 Why It’s Dangerous:
Because the same protocol and key are used for both sides, there's no way to tell that the challenge came from the same party. It allows attackers to bypass authentication without breaking encryption.
🛑 Mitigation Tips:
✅ Use different keys or roles for client/server
✅ Add origin identifiers in challenges
✅ Employ asymmetric authentication if possible
#CyberSecurity #ReflectionAttack #SymmetricEncryption #NetworkSecurity #InfoSecTube #Hacking101 #StaySecure
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⛱A value flow graph (VFG) is a representation of a program's data flow, showing how values are defined and used throughout the code. It's a directed graph where nodes represent definitions and uses of values, and edges represent the flow of data between them. VFGs are used in static analysis to understand how data changes during program execution and are crucial for analyzing things like vulnerabilities, optimizations, and code transformations.
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Defense in depth is a security strategy that uses multiple layers of protection to safeguard assets. It's a proactive approach that aims to deter threats before they happen and mitigate damage if an attack is successful. By layering security controls, defense in depth provides redundancy and helps contain breaches, even if one layer fails.
Examples of Security Controls in a DiD Strategy:
Perimeter Security: Firewalls, intrusion prevention systems.
Network Security: Network segmentation, VPNs.
Endpoint Security: Antivirus, endpoint detection and response (EDR).
Application Security: Security testing, vulnerability management.
Data Security: Encryption, access control lists.
Identity and Access Management: Multi-factor authentication, least privilege principle.
Security Awareness Training: Educating users about potential threats.
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Examples of Security Controls in a DiD Strategy:
Perimeter Security: Firewalls, intrusion prevention systems.
Network Security: Network segmentation, VPNs.
Endpoint Security: Antivirus, endpoint detection and response (EDR).
Application Security: Security testing, vulnerability management.
Data Security: Encryption, access control lists.
Identity and Access Management: Multi-factor authentication, least privilege principle.
Security Awareness Training: Educating users about potential threats.
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⏱️ What is TOTP? (Time-based One-Time Password) 🔐
TOTP stands for Time-based One-Time Password, a widely used algorithm in multi-factor authentication (MFA) that generates a new, temporary password every 30 seconds based on time and a shared secret.
🛠 How It Works:
🔑 A shared secret key
🕒 The current timestamp
Together, these generate a short, unique code — valid for a limited time (usually 30 seconds). After that, it's gone! 🚫
📲 Commonly used in apps like Google Authenticator, Authy, and Microsoft Authenticator.
✅ Why TOTP is Great:
🔒 Codes constantly refresh
💥 Resistant to replay attacks
📶 No need for constant internet — works offline
🚀 Easy to implement and user-friendly
⚠️ Just remember: if your device's time is off, TOTP might not work correctly!
#CyberSecurity #TOTP #2FA #OneTimePassword #MFA #Authentication #InfoSec #StaySecure #AuthApps #TimeBasedSecurity
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TOTP stands for Time-based One-Time Password, a widely used algorithm in multi-factor authentication (MFA) that generates a new, temporary password every 30 seconds based on time and a shared secret.
🛠 How It Works:
🔑 A shared secret key
🕒 The current timestamp
Together, these generate a short, unique code — valid for a limited time (usually 30 seconds). After that, it's gone! 🚫
📲 Commonly used in apps like Google Authenticator, Authy, and Microsoft Authenticator.
✅ Why TOTP is Great:
🔒 Codes constantly refresh
💥 Resistant to replay attacks
📶 No need for constant internet — works offline
🚀 Easy to implement and user-friendly
⚠️ Just remember: if your device's time is off, TOTP might not work correctly!
#CyberSecurity #TOTP #2FA #OneTimePassword #MFA #Authentication #InfoSec #StaySecure #AuthApps #TimeBasedSecurity
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⛑Intermediate code (also known as intermediate representation, or IR) is a machine-independent representation of a program, generated by a compiler as a step between the source code and machine code. It allows for better optimization and portability, making it easier to target different hardware architectures with a single compiler.
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📚 OS Concepts — Deadlocks Made Simple! 🧵
Let’s break down how deadlocks happen, how to avoid them, and how to fix them if things go wrong 💥
🔒 Deadlock Needs 4 Conditions:
Mutual Exclusion → Only one thread uses a resource
Hold & Wait → Hold one lock, wait for another
No Preemption → Can’t force release of resources
Circular Wait → A waits for B, B for C, C for A
🛡 How to Avoid Deadlocks:
🔁 Lock Ordering → Always lock in the same order
✋ Hold & Wait Prevention → Grab all locks at once
🔄 Try-Lock + Retry → Release & retry after random delay
⚙️ Lock-Free (Atomic ops) → Avoid locks entirely
🚨 If Deadlock Happens:
☠️ Kill one thread → Free its resources
⏪ Rollback & Restart → Safer but needs saved state
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Let’s break down how deadlocks happen, how to avoid them, and how to fix them if things go wrong 💥
🔒 Deadlock Needs 4 Conditions:
Mutual Exclusion → Only one thread uses a resource
Hold & Wait → Hold one lock, wait for another
No Preemption → Can’t force release of resources
Circular Wait → A waits for B, B for C, C for A
🛡 How to Avoid Deadlocks:
🔁 Lock Ordering → Always lock in the same order
✋ Hold & Wait Prevention → Grab all locks at once
🔄 Try-Lock + Retry → Release & retry after random delay
⚙️ Lock-Free (Atomic ops) → Avoid locks entirely
🚨 If Deadlock Happens:
☠️ Kill one thread → Free its resources
⏪ Rollback & Restart → Safer but needs saved state
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🌈 Rainbow Table Attack Explained 🔓
A Rainbow Table Attack is a fast and sneaky way to crack passwords by using precomputed tables of hash values and their matching plain-text passwords.
💡 Unlike brute-force attacks (which try every combo one by one), rainbow tables match the hash directly using a huge database of known values.
🔁 Why It Works:
Hash functions are one-way by design — but if you don’t add extra protection (like salting), attackers can reverse them using these tables.
Basically:
👉 You hash a password → attacker finds that hash in their rainbow table → password cracked instantly! ⚠️
🧂 How to Stay Safe:
✅ Always salt your passwords — add random data before hashing.
✅ Use strong hashing algorithms like bcrypt, scrypt, or Argon2.
✅ Never store plain hashes without extra protection.
#CyberSecurity #RainbowTable #PasswordCracking #Hashing #Salting #InfoSec #CyberAttack #StaySecure
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A Rainbow Table Attack is a fast and sneaky way to crack passwords by using precomputed tables of hash values and their matching plain-text passwords.
💡 Unlike brute-force attacks (which try every combo one by one), rainbow tables match the hash directly using a huge database of known values.
🔁 Why It Works:
Hash functions are one-way by design — but if you don’t add extra protection (like salting), attackers can reverse them using these tables.
Basically:
👉 You hash a password → attacker finds that hash in their rainbow table → password cracked instantly! ⚠️
🧂 How to Stay Safe:
✅ Always salt your passwords — add random data before hashing.
✅ Use strong hashing algorithms like bcrypt, scrypt, or Argon2.
✅ Never store plain hashes without extra protection.
#CyberSecurity #RainbowTable #PasswordCracking #Hashing #Salting #InfoSec #CyberAttack #StaySecure
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📚 OS Concepts — What is a Context Switch? 🧵
Ever wonder how your system runs multiple apps at once on one CPU core? The magic is in context switching!
🔁 Context Switch = Save + Swap Process State
🧠 The CPU saves the current process state
📦 Loads another process's state
🚀 Starts running the new process like nothing changed!
🕒 Happens when:
Time slice ends (preemptive multitasking)
Process blocks (waiting for I/O)
OS handles system call
Switching between threads or users
📌 What’s saved?
CPU registers
Stack pointer
Program counter
Memory mapping info
🔐 Stored in the Process Control Block (PCB)
⚠️ Costly Operation
💸 Takes time & resources
📉 Too many = performance drop
✅ Tip: Efficient schedulers reduce unnecessary switches!
#OS #ContextSwitch #Multitasking #Scheduling #ComputerScience
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Ever wonder how your system runs multiple apps at once on one CPU core? The magic is in context switching!
🔁 Context Switch = Save + Swap Process State
🧠 The CPU saves the current process state
📦 Loads another process's state
🚀 Starts running the new process like nothing changed!
🕒 Happens when:
Time slice ends (preemptive multitasking)
Process blocks (waiting for I/O)
OS handles system call
Switching between threads or users
📌 What’s saved?
CPU registers
Stack pointer
Program counter
Memory mapping info
🔐 Stored in the Process Control Block (PCB)
⚠️ Costly Operation
💸 Takes time & resources
📉 Too many = performance drop
✅ Tip: Efficient schedulers reduce unnecessary switches!
#OS #ContextSwitch #Multitasking #Scheduling #ComputerScience
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📚 OS Concepts — How Are System Calls Secure? 🧵
Apps talk to the kernel using system calls — but how does the OS stop them from breaking things? Let’s see 🔒
🔹 1. Trap = Safe Doorbell
🔔 User apps can’t run kernel code directly — they trigger a trap (e.g., int 0x80) to switch modes.
🔹 2. Syscall Table Lookup
📋 Each syscall has a number (like read = 0, write = 1)
🔍 The kernel uses this to safely run a registered handler — no custom functions allowed.
🔹 3. Secure Input Handling
🛡 Kernel checks:
Are pointers valid?
Are arguments safe?
Can this memory be read/written?
No check = no execution.
🔹 4. Safe Copy Functions
🚫 Kernel never touches user memory directly!
✅ Uses:
copy_from_user()
get_user() / put_user()
🔹 5. Return to User Mode
Once done, the OS switches the CPU back to user mode — kernel stays protected.
📌 TL;DR: System calls are like guarded gates. The kernel:
Controls entry
Validates everything
Exits cleanly
#OS #Syscall #Security #KernelMode #Trap #SystemCalls
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Apps talk to the kernel using system calls — but how does the OS stop them from breaking things? Let’s see 🔒
🔹 1. Trap = Safe Doorbell
🔔 User apps can’t run kernel code directly — they trigger a trap (e.g., int 0x80) to switch modes.
🔹 2. Syscall Table Lookup
📋 Each syscall has a number (like read = 0, write = 1)
🔍 The kernel uses this to safely run a registered handler — no custom functions allowed.
🔹 3. Secure Input Handling
🛡 Kernel checks:
Are pointers valid?
Are arguments safe?
Can this memory be read/written?
No check = no execution.
🔹 4. Safe Copy Functions
🚫 Kernel never touches user memory directly!
✅ Uses:
copy_from_user()
get_user() / put_user()
🔹 5. Return to User Mode
Once done, the OS switches the CPU back to user mode — kernel stays protected.
📌 TL;DR: System calls are like guarded gates. The kernel:
Controls entry
Validates everything
Exits cleanly
#OS #Syscall #Security #KernelMode #Trap #SystemCalls
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📚 OS Concepts — Producer-Consumer Problem 🧵
Let’s break down this classic synchronization problem with a tasty example 🍔👇
🔸 Scenario:
A chef (producer) makes burgers 🍔
A customer (consumer) eats them
They share a tray (buffer) with limited space (e.g., 5 slots)
🔸 The Problem:
Chef shouldn't add burgers if the tray is full
Customer shouldn't take burgers if the tray is empty
They shouldn't touch the tray at the same time
🔸 The Solution:
Use semaphores + mutex
empty: Blocks producer if tray is full
full: Blocks consumer if tray is empty
mutex: Stops race conditions on the tray
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Let’s break down this classic synchronization problem with a tasty example 🍔👇
🔸 Scenario:
A chef (producer) makes burgers 🍔
A customer (consumer) eats them
They share a tray (buffer) with limited space (e.g., 5 slots)
🔸 The Problem:
Chef shouldn't add burgers if the tray is full
Customer shouldn't take burgers if the tray is empty
They shouldn't touch the tray at the same time
🔸 The Solution:
Use semaphores + mutex
empty: Blocks producer if tray is full
full: Blocks consumer if tray is empty
mutex: Stops race conditions on the tray
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🔔The Matthews Correlation Coefficient (MCC) is a metric used in machine learning to evaluate the quality of binary classification. It's considered a robust measure, particularly for imbalanced datasets, as it takes into account true and false positives and negatives. MCC values range from -1 to +1, where +1 indicates a perfect prediction, 0 indicates no better than random guessing, and -1 indicates total disagreement.
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