#boot

After editing /etc/default/grub or installing a kernel, rebuild grub.cfg so the boot menu reflects it.

Disable or re-enable Windows Fast Startup (hybrid boot) with the HiberbootEnabled registry value to fix shutdown and dual-boot problems.

Shorten or lengthen how long Windows shows the dual-boot / recovery menu at startup using bcdedit /timeout.

systemd-analyze blame ranks every unit by the time it took to initialize, revealing what delays startup.

One command reboots the PC straight into the firmware settings screen, no keyboard-mashing at startup needed.

Use systemctl reboot --firmware-setup to restart Linux straight into the motherboard's firmware setup screen.

Set the safeboot flag with bcdedit so the next restart starts Windows in Safe Mode, then remove the flag to return to normal boot.

Make Linux boot to a text console to save resources, or restore the graphical desktop as default.

Read the BCD store's boot manager and loader entries before making any boot changes.

Pick which OS or drive boots first by editing the EFI BootOrder variable from a running Linux.

critical-chain prints the chain of units that most delayed reaching the default target, with @ and + markers for start time and duration.

Boot a live USB, mount the installed system and chroot into it so repairs (grub, packages, fstab) run against the real system.