Learn how to locate and verify bootloader settings so the correct kernel and options are used at boot. 16.11.2025 | reading time: 3 min A misconfigured bootloader leaves a system unbootable; a correct file reveals which kernel and command-line options the system will use at startup, so learning to inspect these files is one of the fastest ways to diagnose boot issues. Look inside GRUB’s files Reproduce a common check: view the system-wide defaults and the generated GRUB menu to confirm kernel lines and parameters; example session: ```sudo cat /etc/default/grub # sample output GRUB_DEFAULT=0 GRUB_TIMEOUT_STYLE=menu GRUB_TIMEOUT=5 GRUB_CMDLINE_LINUX="quiet splash" # now inspect generated config for menu entries sudo grep -n "^menuentry" /boot/grub/grub.cfg | sed -n '1,5p' # sample output 1:menuentry 'Linux, with Linux 5.15.0-50-generic' --class gnu-linux --class gnu --class os { 45:menuentry 'Advanced options for Linux' --class gnu-linux --class gnu --class os { # confirm kernel line for the first menu entry sudo sed -n '1,40p' /boot/grub/grub.cfg | sed -n '1,20p'``` What to watch for next Check the `GRUB_CMDLINE_LINUX` setting in `/etc/default/grub` for kernel parameters, inspect scripts in `/etc/grub.d` that add entries, verify that `update-grub` or `grub-mkconfig` was run to regenerate `/boot/grub/grub.cfg`, and on UEFI systems confirm that the EFI boot order matches the expected loader with `efibootmgr` or that systemd-boot has the right loader entries in `/boot/loader/entries`. Quick checks for EFI systems When boots fail only on UEFI machines, list variables with `sudo efibootmgr -v` to see the boot order and file paths, compare those paths to files under `/boot/efi/EFI`, and remember Secure Boot may block unsigned kernels or loaders; adjusting configuration often means editing the loader file and then confirming with a reboot or with `bootctl` for systemd-boot setups. Tools that speed troubleshooting Use `grub-mkconfig` or `update-grub` to rebuild GRUB configs after edits, `efibootmgr` to inspect and change EFI boot entries, and `bootctl` for systemd-boot to list and verify loader entries; running these commands with sudo gives the immediate view you need to decide the next step. Wrap-up and next steps Inspecting bootloader files is a small diagnostic habit that prevents large outages: read the defaults, confirm the generated menu, and check EFI tables when relevant; keep practicing these checks and consider formal study to deepen understanding and exam readiness through resources like bitsandbytes.academy for CompTIA Linux+ or LPIC-1 preparation. Join Bits & Bytes Academy First class LINUX exam preparation. boot-process setup utilities troubleshooting
