An operating system (OS) is the low-level software that manages resources, controls peripherals, and provides basic services to other software. In Linux, there are 6 distinct stages in the typical booting process.
In this stage of the boot process, the kernel that was selected by GRUB first mounts the root file system that's specified in the grub.conf file. Then it executes the /sbin/init program, which is always the first program to be executed. You can confirm this with its process id (PID), which should always be 1.
Linux startup process
Download Zip: https://glutitxtagbu.blogspot.com/?download=2vFXWg
If you look in the different run level directories, you'll find programs that start with either an "S" or "K" for startup and kill, respectively. Startup programs are executed during system startup, and kill programs during shutdown.
The information here all seems correct, however I think you do a disservice to the reader not to mention that this is just one of many different ways to load Linux on a PC architecture. Other architectures use other methods, and there are other methods available on a PC architecture, and the version and configuration of the Linux kernel itself affects the boot process.
Booting a Linux installation involves multiple stages and software components, including firmware initialization, execution of a boot loader, loading and startup of a Linux kernel image, and execution of various startup scripts and daemons. For each of these stages and components there are different variations and approaches; for example, GRUB, coreboot or Das U-Boot can be used as boot loaders (historical examples are LILO, SYSLINUX or Loadlin), while the startup scripts can be either traditional init-style, or the system configuration can be performed through modern alternatives such as systemd or Upstart.
Early stages of the Linux startup process depend very much on the computer architecture. IBM PC compatible hardware is one architecture Linux is commonly used on; on these systems, the BIOS plays an important role, which might not have exact analogs on other systems. In the following example, IBM PC compatible hardware is assumed:
On shutdown, init is called to close down all user space functionality in a controlled manner. Once all the other processes have terminated, init makes a system call to the kernel instructing it to shut the system down.
The boot loader phase varies by computer architecture. Since the earlier phases are not specific to the operating system, the BIOS-based boot process for x86 and x86-64 architectures is considered to start when the master boot record (MBR) code is executed in real mode and the first-stage boot loader is loaded. In UEFI systems, the Linux kernel can be executed directly by UEFI firmware via EFISTUB,[1] but usually uses GRUB 2 or systemd-boot as a boot loader. Below is a summary of some popular boot loaders:
The kernel is typically loaded as an image file, compressed into either zImage or bzImage formats with zlib. A routine at the head of it does a minimal amount of hardware setup, decompresses the image fully into high memory, and takes note of any RAM disk if configured.[4] It then executes kernel startup via ./arch/i386/boot/head and the startup_32 () (for x86 based processors) process.
The startup function for the kernel (also called the swapper or process 0) establishes memory management (paging tables and memory paging), detects the type of CPU and any additional functionality such as floating point capabilities, and then switches to non-architecture specific Linux kernel functionality via a call to start_kernel().[5]
start_kernel executes a wide range of initialization functions. It sets up interrupt handling (IRQs), further configures memory, starts the Init process (the first user-space process), and then starts the idle task via cpu_idle(). Notably, the kernel startup process also mounts the initial RAM disk ("initrd") that was loaded previously as the temporary root file system during the boot phase. The initrd allows driver modules to be loaded directly from memory, without reliance upon other devices (e.g. a hard disk) and the drivers that are needed to access them (e.g. a SATA driver). This split of some drivers statically compiled into the kernel and other drivers loaded from initrd allows for a smaller kernel. The root file system is later switched via a call to pivot_root() which unmounts the temporary root file system and replaces it with the use of the real one, once the latter is accessible. The memory used by the temporary root file system is then reclaimed.
Thus, the kernel initializes devices, mounts the root filesystem specified by the boot loader as read only, and runs Init (/sbin/init) which is designated as the first process run by the system (PID = 1).[6] A message is printed by the kernel upon mounting the file system, and by Init upon starting the Init process. It may also optionally run Initrd[clarification needed] to allow setup and device related matters (RAM disk or similar) to be handled before the root file system is mounted.[6]
At this point, with interrupts enabled, the scheduler can take control of the overall management of the system, to provide pre-emptive multi-tasking, and the init process is left to continue booting the user environment in user space.
initramfs, also known as early user space, has been available since version 2.5.46 of the Linux kernel,[7] with the intent to replace as many functions as possible that previously the kernel would have performed during the startup process. Typical uses of early user space are to detect what device drivers are needed to load the main user space file system and load them from a temporary filesystem. Many distributions use dracut to generate and maintain the initramfs image.
Once the kernel has started, it starts the init process. Historically this was the "SysV init", which was just called "init". More recent Linux distributions are likely to use one of the more modern alternatives such as systemd.
Every time you power on your Linux PC, it goes through a series of stages before finally displaying a login screen that prompts for your username or password. There are 4 distinct stages that every Linux distribution goes through in a typical boot-up process.
In some cases, a beeping sound will go off especially in the event of a missing RAM module. However, if the expected hardware is present and functioning as expected, the booting process proceeds to the next stage.
The kernel finally loads Systemd, which is the replacement of the old SysV init. Systemd is the mother of all Linux processes and manages among other things mounting of file systems, starting and stopping services to mention just a few.
Sure. Just give me some time to go through more content on your site and then I will tell you where you can make changes. I am studying operating systems and linux and so would like to help because this will increase my knowledge as well. I will get back to you in a few days as I am working
In order to boot Arch Linux, a Linux-capable boot loader must be set up. The boot loader is responsible for loading the kernel and initial ramdisk before initiating the boot process. The procedure is quite different for BIOS and UEFI systems. A detailed description is given on this or linked pages.
A BIOS or Basic Input-Output System is in most cases stored in a flash memory in the motherboard itself and independent of the system storage. Originally created for the IBM PC to handle hardware initialization and the boot process, it has been replaced progressively since 2010 by the UEFI which does not suffer from the same technical limitations.
The purpose of the initramfs is to bootstrap the system to the point where it can access the root file system (see FHS for details). It does not need to contain every module one would ever want to use; it should only have modules required for the root device like IDE, SCSI, SATA or USB/FW (if booting from an external drive) and encryption. The majority of modules will be loaded later on by udev, during the init process.
The startup of late userspace is executed by the init process. Arch officially uses systemd which is built on the concept of units and services, but the functionality described here largely overlaps with other init systems.
The init process calls getty once for each virtual terminal (typically six of them). getty initializes each terminal and protects it from unauthorized access. When the username and password are provided, getty checks them against /etc/passwd and /etc/shadow, then calls login(1).
During a computer's boot process, you must transition from a firmware (UEFI or BIOS) process to loading a kernel and then finally to the user environment. When booting a POSIX system, you can choose to interrupt the boot process to adjust settings or even to log in using a chroot environment.
This is a useful troubleshooting and maintenance technique, but it's also the reason it's so important to utilize full disk encryption when installing your operating system. When a drive is encrypted, nothing on the drive is accessible without your passphrase, even from a preboot environment. As long as you have the passphrase to decrypt your drive, you can interrupt a Linux system's boot process and access the drive without booting into a full operating system (OS).
To prepare your computer to have its boot process interrupted, press e on your keyboard when you see the GRUB startup screen. This reveals the boot parameters assigned to the default menu selection.
Because you've instructed the initrd to break, the boot process stops in an emergency maintenance mode. If you have nothing you need to do, you can press Ctrl+D to continue booting as normal. Otherwise, press Enter for a minimal but interactive shell.
To recover a password, you might need to remount the drive (it's already mounted in read-only mode to /sysroot as part of the boot process). The remount,rw options mount a location on a drive with write permissions. This task can be extremely dangerous: You have full root privileges, no guardrails, and a writable drive. The less time you spend in this mode, the better, and you should use it only in true emergencies. 2ff7e9595c
Comentários