This is a topic that I haven’t reviewed much or probably nothing at all. When your Linux system boots, GRUB loads the Linux kernel and passes its options. These kernel options can help us:
- Debug boot issues
- Enable or disable hardware drivers
- Enter specific modes (like single-user)
When to use bootloader GRUB command at boot time?
- Troubleshooting boot problems
- Disabling a problematic device driver
- Entering rescue or single-user mode
- Disabling graphical splash or enabling logs
- Passing custom memory or CPU settings
You can pass kernel command parameters to GRUB at boot time or make it permanent. For now, I’m going to decide which coffee from Latin America I’m going to brew at home.
Pass kernel parameters temporarily
Interrupt GRUB at boot time and when the menu appears do:
Press e to edit the boot entry.You may see this line:
linux /boot/vmlinuz-5.15.0-91-generic root=UUID=xxxx ro quiet splashYou can append options at the end of the line starting with linux. For example to boot into single-user mode:
linux /boot/vmlinuz-... root=UUID=... ro singleor
linux /boot/vmlinuz-... root=UUID=... ro init=/bin/bashCommon used kernel boot options
| Option | Purpose | Example Usage |
|---|
single | Boot into single-user mode | linux ... ro single |
init=/bin/bash | Start with Bash shell instead of init/systemd | linux ... ro init=/bin/bash |
nomodeset | Prevent kernel mode-setting (graphics troubleshooting) | linux ... ro quiet splash nomodeset |
quiet | Suppresses most boot messages | linux ... ro quiet |
splash | Show splash screen | linux ... ro splash |
noapic, nolapic | Disables APIC / Local APIC (used for IRQ troubleshooting) | linux ... noapic nolapic |
acpi=off | Disables ACPI (power management, battery issues) | linux ... acpi=off |
mem=512M | Limit usable memory | linux ... mem=512M |
root=/dev/sdXn | Specify root device (overrides default) | linux ... root=/dev/sda1 |
Make changes permanent if you want
Edit /etc/default/grub with your favorite editor. I like to use vim.
Find this line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"Modify it using the options in the table above. For example you can do:
GRUB_CMDLINE_LINUX_DEFAULT="quiet single nomodeset"Then update GRUB:
sudo update-grub # Debian/Ubuntusudo grub2-mkconfig -o /boot/grub2/grub.cfg # RHEL/CentOSView the current kernel command line configuration
You can simply run this command in your Terminal:
cat /proc/cmdlineYou should see something like this:
Keep in mind the below for Linux bootloader
- Always test kernel parameters temporarily first.
- If a parameter causes issues, reboot and remove it.
- Kernel parameters are space-separated.