This guide explains how to access the GRUB (GRand Unified Bootloader) menu on a Linux system, where you can choose between kernels, edit boot parameters, drop into rescue mode, or chain-load other operating systems.
NOTE
When GRUB shows up by default: in dual-boot setups and on most server installs, GRUB appears at every boot with a few-second timeout. On single-OS desktop installs (Ubuntu, Fedora…) it’s typically hidden behind a zero-second timeout, so you have to force it to appear.
Check if GRUB is your bootloader
Before trying any method, confirm GRUB is what your system actually uses (some modern minimal installs use systemd-boot or rEFInd instead).
From a running Linux
Check for GRUB’s installation directory:
ls /boot/grub/ 2>/dev/null || ls /boot/grub2/ 2>/dev/null
Result
Bootloader
grub.cfg, fonts/, themes/
✅ GRUB
Both fail
❌ Probably systemd-boot or rEFInd
You can also verify with:
sudo bootctl status
If bootctl reports systemd-boot, this guide doesn’t apply to you.
Enter the GRUB
1. Interrupt the boot (the classic way)
The historic and most universal method: catch GRUB’s tiny timeout window with the right key press, right after the firmware POST.
Hold Shift or tap Esc
Reboot the system normally.
The moment the firmware screen (BIOS/UEFI vendor logo) disappears, start pressing:
Boot mode
Key
Legacy BIOS
Hold Shift
UEFI (modern GRUB)
Tap Esc repeatedly
Some OEMs (rare)
F4
The GRUB menu appears with the list of kernels.
Timing matters: start after POST, otherwise the firmware itself grabs the key.
If you can't catch the timing
The window can be a few hundred milliseconds: UEFI Fast Boot is the enemy here.
Disable Fast Boot in the firmware settings (see BIOS).
This is a workaround: the real fix is Method 3 below.
2. From a running Linux (systemd ≥ 240)
If you’re already inside Linux and want the next reboot to land in GRUB automatically:
One-shot systemctl flag
sudo systemctl reboot --boot-loader-menu=3
Tells systemd to ask the bootloader to display the menu for 3 seconds on the next boot, then forget the override.
GRUB will now show the menu for 5 seconds at every boot. Use GRUB_TIMEOUT=-1 to wait indefinitely (good for headless servers where you want a human to confirm before booting).
⚠️ Last Resort: live USB rescue
If GRUB is corrupted (no menu, no shell, kernel panic, or “no bootable device”) and none of the above gets you in:
Boot from a live USB of your distribution.
Mount your root partition: sudo mount /dev/sdaX /mnt
(If /boot is separate) mount it too: sudo mount /dev/sdaY /mnt/boot
Bind-mount the system dirs and chroot:
for d in dev proc sys run; do sudo mount --bind /$d /mnt/$d; donesudo chroot /mnt
Reinstall GRUB and regenerate the config:
grub-install /dev/sdaupdate-grub
This rewrites the GRUB stage-1 in the boot sector / EFI partition and regenerates grub.cfg from scratch.
