efibootmgr

efibootmgr is a command-line utility for managing UEFI boot entries. It allows users to create, modify, and delete boot entries, as well as change the boot order for UEFI-based systems. This tool is essential for managing the boot process on systems with UEFI firmware.

Basic Usage

The basic syntax for efibootmgr is:

efibootmgr [options]

Common Options

• -v, --verbose: Increase verbosity, showing detailed information about the boot entries.

• -b ####, --bootnum ####: Specify the boot entry number to modify (e.g., 0000).

• -B, --delete-bootnum: Delete the specified boot entry.

• -c, --create: Create a new boot entry.

• -n ####, --bootnext ####: Set the boot entry for the next boot only.

• -o ####,####,..., --bootorder ####,####,...: Set the boot order.

• -t ####, --timeout ####: Set the boot manager timeout (in seconds).

Examples

Viewing Current Boot Entries

To list all current boot entries and their details:

efibootmgr -v

This command displays all UEFI boot entries, including the boot order, boot entries, and the associated details.

Creating a New Boot Entry

To create a new boot entry for a Linux kernel:

efibootmgr --create --disk /dev/sda --part 1 --label "MyLinux" --loader /vmlinuz-5.4.0-26-generic

• --disk /dev/sda: Specifies the disk where the boot loader is located.

• --part 1: Specifies the partition number where the boot loader is located.

• --label "MyLinux": Provides a label for the boot entry.

• --loader /vmlinuz-5.4.0-26-generic: Specifies the path to the boot loader.

Deleting a Boot Entry

To delete a specific boot entry (e.g., Boot0003):

efibootmgr --delete-bootnum --bootnum 0003

Setting the Boot Order

To change the boot order, you can specify a new sequence of boot entry numbers:

efibootmgr --bootorder 0001,0002,0003

This command sets the boot order to prioritize Boot0001, followed by Boot0002, and then Boot0003.

Setting the Next Boot Entry

To set a specific boot entry to be used for the next boot only:

efibootmgr --bootnext 0002

This command will set Boot0002 as the boot entry for the next boot. After that boot, the system will revert to the regular boot order.

Troubleshooting

Common Issues

1. Permission Denied: Ensure you run efibootmgr with root privileges, typically by using sudo.

2. No EFI Variables Found: This usually indicates that the system is not booted in UEFI mode. Ensure your system is in UEFI mode and not legacy BIOS mode.

3. EFI Variables Are Read-Only: Some systems may lock the EFI variables, preventing modifications. This can often be resolved by changing settings in the UEFI firmware or ensuring the correct boot mode.

Conclusion

efibootmgr is a powerful utility for managing UEFI boot entries and the boot order on UEFI-based systems. It's particularly useful for managing multi-boot environments, recovering from boot issues, and configuring new boot entries for custom kernels or operating systems. Understanding how to use efibootmgr effectively can significantly enhance your ability to control the boot process on modern systems.