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F.4. The Kernel

When the kernel is loaded, it immediately initializes and configures the computer's memory and configures the various hardware attached to the system, including all processors, I/O subsystems, and storage devices. It then loads the initramfs image(s) from disk and decompresses it into a tmpfs as the acting root filesystem. The initramfs contains programs and kernel modules required to continue booting the system, such as those used to initialize virtual devices related to file systems, like LVM or software RAID.
The kernel uses the initramfs to continue the boot process, and when the final root device is available, the initramfs is unmounted and the real root filesystem is mounted in its place.
At this point, the kernel is loaded into memory and operational. However, since there are no user applications that allow meaningful input to the system, not much can be done with the system.
To set up the user environment, the kernel executes the system daemon, systemd.