Linux 101 : The boot process
Below is a simplified diagram of the boot process of a Linux system:
The UFEI is the new version of the BIOS and the GPT is the new version of the MBR
BIOS/UEFI looks for a bootable device, then loads the primary boot loader from the boot partition - MBR/GPT -.
The boot loader - GRUB - locates the kernel and loads the initrd image into the memory.
Remark:
The kernel takes over and loads the hardware drivers.
The kernel mounts the root partition, and it runs the systemd process which has the first process ID - ID=1 -
The systemd process checks the "default.target" file to know which programs it needs to load, it also mounts the partitions after checking the "/etc/fstab" file.
The kernel mounts the root partition, and it runs the systemd process which has the first process ID - ID=1 -
The systemd process checks the "default.target" file to know which programs it needs to load, it also mounts the partitions after checking the "/etc/fstab" file.
The default target us usually the "multi-user.target" or the "graphical.target"
Initrd - initial ramdisk - loads a temporary root filesystem into the RAM to be able to initiate the system before the actual root filesystem is mounted.
Initrd makes the boot process lighter since it only uses a small portion of the kernel to start the system.
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