1. Managing Kernels and System Boot
  2. About System Boot
  3. About BIOS-Based Booting

About BIOS-Based Booting

On a BIOS-based system running the Oracle Linux release, the boot process is as follows:

  1. The system's BIOS performs a power-on self-test (POST), and then detects and initializes any peripheral devices and the hard disk.

  2. The BIOS reads the Master Boot Record (MBR) into memory from the boot device. The MBR stores information about the organization of partitions on that device, the partition table, and the boot signature which is used for error detection. The MBR also includes the pointer to the boot loader program (GRUB 2), usually on a dedicated /boot partition on the same disk device.

  3. The boot loader loads the vmlinuz kernel image file and the initramfs image file into memory. The kernel then extracts the contents of initramfs into a temporary, memory-based file system (tmpfs).

  4. The kernel loads the driver modules from the initramfs file system that are needed to access the root file system.

  5. The kernel searches for the init process within initramfs and starts the defined process with a process ID of 1 (PID 1). On Oracle Linux, the default init process is configured as systemd. See Oracle Linux 8: Managing the System With systemd for more information.

  6. systemd runs any other processes defined for it.

    Note:

    Specify any other actions to be processed during the boot process by defining systemd units. This method is preferred to using the /etc/rc.local file.