System Architecture
System Architecture
The 101 exam treats hardware and boot as one connected story. Know the boot sequence cold: firmware (BIOS or UEFI) → bootloader (GRUB2) → kernel plus initramfs → init/systemd. GRUB2's configuration is generated, not hand-edited: /boot/grub/grub.cfg (BIOS) or /boot/efi/EFI/<distro>/grub.cfg (UEFI) is produced by grub-mkconfig/grub2-mkconfig from /etc/default/grub and /etc/grub.d/*. grub-install writes the bootloader to disk; changing kernel parameters means editing GRUB_CMDLINE_LINUX and regenerating.
Hardware topics: IRQ, I/O ports, DMA, and the sysfs/procfs views (/proc/interrupts, /proc/ioports, /proc/dma, lspci, lsusb, lsblk). Coldplug vs hotplug, and udev creating /dev entries. Know the difference between kernel modules (lsmod, modprobe, insmod, modinfo, depmod) and where module options live (/etc/modprobe.d/*.conf), plus blacklisting.
For systemd, understand units, targets, systemctl verbs, and that SysV compatibility exists via systemctl enable/disable and chkconfig-style wrappers. Also know dmesg/journalctl -k for kernel messages, uptime/load average, and pgrep/ps for process inspection.
Trap: exam items conflate /etc/default/grub edits with immediate effect. Editing it does nothing until you regenerate the config. Another common trap: modprobe reads dependency info from modules.dep (built by depmod), while insmod takes a bare file path and resolves nothing.
Rule of thumb: if a boot question says "persistent" or "survives reboot," the answer involves writing configuration to disk (grub.cfg, systemd unit enabled, /etc/modprobe.d), never a runtime command alone.