mkinitcpio
also: initramfs generator, initrd builder
A tool that generates an initial ramdisk image (initramfs) required to boot a Linux system, containing essential modules, binaries, and scripts needed before the main root filesystem is mounted.
mkinitcpio is Arch Linux's utility for creating the initramfs—a compressed filesystem image loaded into RAM during boot. It runs before the kernel mounts the real root filesystem, handling hardware detection, loading necessary drivers, and executing boot hooks.
The tool reads configuration from /etc/mkinitcpio.conf, which specifies which modules, binaries, and hooks to include. Common hooks handle RAID, LVM, encryption (dm-crypt), and filesystem support.
Example: after installing a new kernel, you run mkinitcpio -p linux to regenerate the initramfs for that kernel. Without a proper initramfs, the system cannot find or mount the root partition.
Other distributions use similar tools: Fedora/RHEL use dracut, Debian/Ubuntu use initramfs-tools, but the concept and purpose remain identical.