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In the 1950s programmers wrote directly to hardware, but the fragility of hard‑coded memory and I/O led to the invention of a privileged “expert” kernel mode and a restricted “novice” user mode, with a special instruction to switch, forming the basis of modern system calls and operating system protection.
This article provides a comprehensive analysis of the Linux kernel's task_struct data structure, detailing its members such as task IDs, parent‑child relationships, state flags, credentials, scheduling information, signal handling, memory and file management, kernel stack layout, and its role in process creation via system calls like fork.
This article provides a comprehensive overview of the Linux ptrace system call, explaining its role in process debugging, detailing request parameters, demonstrating practical C examples for tracing system calls, single‑stepping, setting breakpoints, and exploring how DWARF debugging information links source code to executable addresses.
This article provides a comprehensive overview of how Linux kernel system calls are implemented on the x86-64 architecture, covering the conceptual differences from regular function calls, register conventions, initialization processes, syscall tables, and practical assembly examples such as write and getpid.
This article explains the Linux poll() system call, detailing its pollfd structure, event flags, parameters like nfds and timeout, return values, and step‑by‑step operation flow for reading and writing data, highlighting differences from select and its advantages on 32‑bit systems.
This article explains the concept of system calls, how they provide a privileged interface between user programs and the kernel, distinguishes them from APIs and library functions, and describes their role in Linux operating‑system architecture and application development.
This article explains Linux memory mapping (mmap), covering its purpose, API parameters, different mapping types, internal kernel implementation, page‑fault handling, copy‑on‑write semantics, practical use cases, and includes a complete Objective‑C example demonstrating file mapping and manipulation.
Researchers from Shanghai Jiao Tong University, Ant Security Light-Year Lab, and Zhejiang University present HODOR, a system that reduces the attack surface of Node.js applications by generating fine-grained system‑call allowlists using Seccomp, achieving an average 80% reduction in exploit surface with negligible runtime overhead.
This article explains how Linux traditional read/write system calls work, detailing the CPU, DMA copies and context switches involved, and then explores high‑performance I/O techniques such as zero‑copy, multiplexing and PageCache, together with the Linux I/O stack and buffering layers.
This article explains core operating‑system concepts such as processes, threads, their control blocks and contexts, details how CPU, process, and thread context switches and system calls work on Linux, and shows how to analyze them with vmstat, pidstat, and sysbench for performance tuning.
The Linux community announced the first release candidate of the 5.14 kernel, featuring contributions from about 1,650 developers, over 13,000 commits, new memfd_secret system call, extensive driver and architecture updates, and numerous core subsystem enhancements.
The PHP chroot() function changes the current process's root directory to a specified path, works only on supported systems in CLI/CGI/embedded SAPI with root privileges, returns TRUE on success or FALSE on failure, and is illustrated with a simple example.
This article explains the concepts of kernel space and user space in a 32‑bit OS, why they are separated, the distinction between kernel mode and user mode, how processes transition between them, and the overall Linux system structure.
The article explains PHP’s chgrp function, which changes a file’s group ownership, outlines its syntax, required parameters, permission restrictions, return values, and provides a complete PHP example demonstrating how to modify a file’s group and display the result.
Linux system calls provide the interface between user programs and the kernel, and this article explains the three implementation methods—software interrupts, fast syscall instructions (SYSENTER/SYSCALL), and the virtual dynamic shared object (vDSO)—detailing their operation, performance impact, and relevant assembly code examples.
This article explains what an IDT is, how it is initialized, the structure of interrupt descriptor entries and gates, the implementation of traditional system calls via int 0x80, and the setup and handling of hardware interrupts in the Linux kernel.
This article explains Linux’s virtual address space, the mmap system call, its prototype and typical applications—including shared file mapping, inter‑process communication, and file I/O optimization—while illustrating concepts with diagrams and code examples, and discusses alignment, copy‑on‑write, and memory swapping considerations.
This article explains how the Linux init process (pid 1) transitions from kernel mode to user mode using kernel_execve and the int 0x80 system call, detailing the register changes, assembly flow, and verification experiment that reveal the privilege level switch.