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Operating System FoundationsUnlike proprietary platforms such as Windows, Linux represents a family of open-source, Unix-like operating systems designed for free distribution and modification. Its architecture adheres to POSIX standards, enabling robust multi-user, multitasking, and multi-threading environments across both 32-bit and 64-bit inf ...

1. Core Cnocepts Linux kernel's task scheduling is complex, but we'll focus on how CGroup limits CPU usage in the CFS scheduler. This explanation simplifies the process by omiting nested CGroup scenarios and using CentOS 7.6 (3.10.0-957.el7) kernel code as reference. 2. Basic CGroup CPU Configuration To create a CGroup named 'test' with CPU lim ...

File System Layer Architecture Before exploring page cache, understanding the file system layer architecture provides essential context for comprehending how data flows through the Linux kernel. 1 VFS Layer The Virtual File System (VFS) layer serves as a generic abstraction for file operations in Linux. It consolidates common functionalities sh ...

The cpufreq infrastructure in Linux allows for dynamic adjustment of processor clock speeds to balance performance and power consumption. This subsystem exports its configuration through the sysfs interface, usually found at /sys/devices/system/cpu/cpu[N]/cpufreq/. By modifying specific files in this directory, users can control how the kernel ...

14.5 File Creation 14.5.1 The file_create Implementation When creating a new file, several critical operations must be performed in sequence: Inode Allocation: Each file requires an inode to track its size, location, and metadata. The process begins by allocating an inode number from the inode bitmap. This involves updating the inode bitmap, ...

Understanding the /proc Virtual File System The /proc directory serves as a virtual file system in Linux that provides access to kernel and process information through file-like interfaces. This system acts as a window into the kernel's data structures, allowing users and applications to retrieve system information without making direct system ...

Inspecting Process Memory Usage Using top PID – Process ID USER – Owner PR – Priority (lower = higher) NI – Nice value VIRT – Virtual memory RES – Physical memory SHR – Shared memory S – State (S=sleep, R=run, Z=zombie, N=negative nice) %CPU – CPU usage %MEM – Physical memory ratio TIME+ – Cumulative CPU time COMMAND – Execu ...

Modern applications rely on complex execution environments—ranging from standard libraries to operating systems—to manage resources and hardware interactions. To build a kernel from scratch, one must strip away these abstractions and interface directly with the CPU and memory. This process involves navigating the target platform's architecture, ...

Memory Layout and Page Table Management Hardware Device Mapping Hardware devices like UART0 (0x10000000L), VIRTIO0, CLINT, and PLIC have fixed physical addresses and interrupt numbers defined by hardware design. The kernel uses these addresses to communicate with devices, initialize registers, and handle interrupts. Kernel Loading and Execution ...

Process Concealment via Procfs Mounting In Linux environments, process metadata is exposed via the /proc pseudo-filesystem. Standard monitoring utilities like ps, top, and htop retrieve system information by reading the subdirectories within /proc that correspond to specific Process IDs (PIDs). By utilizing the mount command with the --bind fla ...