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Linux startup process is the multi-stage initialization process performed during booting a Linux installation. It is in many ways similar to the BSD and other Unix-style boot processes, from which it derives. 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, LILO, SYSLINUX or Loadlin can be used as boot loaders, while the startup scripts can be either traditional init-style, or the system configuration can be performed through more modern alternatives such as systemd or Upstart. == Overview == 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: # The BIOS performs startup tasks specific to the actual hardware platform. Once the hardware is enumerated and the hardware which is necessary for boot is initialized correctly, the BIOS loads and executes the boot code from the configured boot device. # The boot loader often presents the user with a menu of possible boot options and has a default option, which is selected after some time passes. Once the selection is made, the boot loader loads the kernel into memory, supplies it with some parameters and gives it control. # The kernel decompresses itself, sets up system functions such as essential hardware and memory paging, and calls start_kernel() which performs the majority of system setup (interrupts, the rest of memory management, device and driver initialization, etc). It then starts up, separately, the idle process, scheduler, and the init process, which is executed in user space.# The init either consists of scripts that are executed by the shell (sysv, bsd, runit) or configuration files that are executed by the binary components (systemd, upstart). Init has specific levels (sysv, bsd) or targets (systemd), each of which consists of specific set of services (daemons). These provide various non-operating system services and structures and form the user environment. A typical server environment starts a web server, database services, and networking. # The typical desktop environment begins with a daemon, called the display manager, that starts a graphic environment which consists of a graphical server that provides a basic underlying graphical stack and a login manager that provides the ability to enter credentials and select a session. After the user has entered the correct credentials, the session manager starts a session. A session is a set of programs such as UI elements (panels, desktops, applets, etc) which, together, can form a complete desktop environment. On shutdown, all init is called to close down all user space functionality in a controlled manner. The init then terminates and the kernel executes its own shutdown. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Linux startup process」の詳細全文を読む スポンサード リンク
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