Booting the Linux operating system:
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The first thing a computer does on start-up is a primer test (POST - Power On Self Test). This way several devices are tested, including the processor, memory, graphics card and the keyboard. Here is tested the boot medium (hard disk, floppy unit, CD-ROMs). After POST, the loader from a ROM loads the boot sector, which in turn loads the operating system from the active partition.
The boot blocks is always at the same place: track 0, cylinder 0, head 0 of the device from which we're booting. This block contains a program called loader, which in Linux's case is LiLo (Linux Loader), or Grub (GNU Grub Unified Boot Loader), which actually boots the operating system. These loaders in Linux , in case of a multi-boot configuration (more operating systems on a computer), permit the selection of the operating system to be booted. Lilo and Grub are installed or at the MBR (Master Boot Record), or at the first sector of the active partition.
In the following we will refer to LiLO as boot loader. This is usually installed in the boot sector, also known as MBR. If the user decides to boot Linux, LiLo will try to load the kernel. Now I will present step-by-step LiLo's attempt to load the operating system.
1. In case of a multi-boot config, LiLo permits the user two choose an operating system from the menu. The LiLo settings are stored at /etc/lilo.conf. System administrators use this file for a very detailed finement of the loader. Here can be manually set what operating systems are installed, as well as the method for loading any of them. If on the computer there is only Linux, LiLo can be set to load directly the kernel, and skip the selection menu.
2. The Linux kernel is compressed, and contains a small bit, which will decompress it. Immediately after the first step begins the decompression and the loading of the kernel.
3. If the kernel detects that your graphics card supports more complex text modes, Linux allows the usage of them - this can be specified or during the recompilation of the kernel, or right inside Lilo, or other program, like rdev.
4. The kernel verifies hardware configuration (floppy drive, hard disk, network adapters, etc) and configures the drivers for the system. During this operation, several informative messages are shown to the user.
5. The kernel tries to mount the file system and the system files. The location of system files is configurable during recompilation, or with other programs - LiLo and rdev. The file system type is automatically detected. The most used file systems on Linux are ext2 and ext3. If the mount fails, a so-called kernel panic will occur, and the system will "freeze".
System files are usually mounted in read-only mode, to permit a verification of them during the mount. This verification isn't indicated if the files were mounted in read-write mode.
6. After these steps, the kernel will start init, which will become process number 1, and will start the rest of the system.
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The first thing a computer does on start-up is a primer test (POST - Power On Self Test). This way several devices are tested, including the processor, memory, graphics card and the keyboard. Here is tested the boot medium (hard disk, floppy unit, CD-ROMs). After POST, the loader from a ROM loads the boot sector, which in turn loads the operating system from the active partition.
The boot blocks is always at the same place: track 0, cylinder 0, head 0 of the device from which we're booting. This block contains a program called loader, which in Linux's case is LiLo (Linux Loader), or Grub (GNU Grub Unified Boot Loader), which actually boots the operating system. These loaders in Linux , in case of a multi-boot configuration (more operating systems on a computer), permit the selection of the operating system to be booted. Lilo and Grub are installed or at the MBR (Master Boot Record), or at the first sector of the active partition.
In the following we will refer to LiLO as boot loader. This is usually installed in the boot sector, also known as MBR. If the user decides to boot Linux, LiLo will try to load the kernel. Now I will present step-by-step LiLo's attempt to load the operating system.
1. In case of a multi-boot config, LiLo permits the user two choose an operating system from the menu. The LiLo settings are stored at /etc/lilo.conf. System administrators use this file for a very detailed finement of the loader. Here can be manually set what operating systems are installed, as well as the method for loading any of them. If on the computer there is only Linux, LiLo can be set to load directly the kernel, and skip the selection menu.
2. The Linux kernel is compressed, and contains a small bit, which will decompress it. Immediately after the first step begins the decompression and the loading of the kernel.
3. If the kernel detects that your graphics card supports more complex text modes, Linux allows the usage of them - this can be specified or during the recompilation of the kernel, or right inside Lilo, or other program, like rdev.
4. The kernel verifies hardware configuration (floppy drive, hard disk, network adapters, etc) and configures the drivers for the system. During this operation, several informative messages are shown to the user.
5. The kernel tries to mount the file system and the system files. The location of system files is configurable during recompilation, or with other programs - LiLo and rdev. The file system type is automatically detected. The most used file systems on Linux are ext2 and ext3. If the mount fails, a so-called kernel panic will occur, and the system will "freeze".
System files are usually mounted in read-only mode, to permit a verification of them during the mount. This verification isn't indicated if the files were mounted in read-write mode.
6. After these steps, the kernel will start init, which will become process number 1, and will start the rest of the system.
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