The „Unified Extensible Firmware Interface“ is a specification for software interfaces between the firmware and the operation system. It has replaced the legacy-bios and is capable of secureboot features. So far so good…
But the time may come when you wish to change your UEFI-boot-order or get rid of some old entiries.
There’s a handy tool for exactly this purpose, called efibootmgr.
From reading through the manpages, efibootmgr is a userspace application used to modify the UEFI Boot Manager.
Which means, it gives us the opportunity to manipulate the efi bootorder or create and delete UEFI-boot entries. This is great :)

Installation

On my t460s I am running gentoo, so I just executed emerge -va sys-boot/efibootmgr, to install this package¹:

*  sys-boot/efibootmgr
      Latest version available: 16
      Latest version installed: 16
      Size of files: 36 KiB
      Homepage:      https://github.com/rhinstaller/efibootmgr
      Description:   User-space application to modify the EFI boot manager
      License:       GPL-2

On debian-based systems you should be able to run something like sudo apt install efibootmgr to install it – if it isn’t installed by default.
(on CentOS systems you probaply type yum install efibootmgr, I suppose)

¹I am using the -v (--verbose) and the -a (--ask) options here. The first one to see which Flags will be used. Most of the times I want to change them so I answer No when emerge asks me. So this is why I’m using -a. You could even use -p (--pretend) to see the flags, change them and run emerge without these options.

Usage

See entries / get informations

If you run efibootmgr without any options¹, you might get a output similar to this one:

# efibootmgr
BootCurrent: 0002
Timeout: 2 seconds
BootOrder: 0002,0017,0018,0019,001A,001B,001C,0021,0003
Boot0002* gentoo
Boot0003* Linux-Firmware-Updater
Boot0010  Setup
Boot0011  Boot Menu
Boot0012  Diagnostic Splash Screen
Boot0013  Lenovo Diagnostics
Boot0014  Startup Interrupt Menu
Boot0015  Rescue and Recovery
Boot0016  MEBx Hot Key
Boot0017* USB CD
Boot0018* USB FDD
Boot0019* NVMe0
Boot001A* ATA HDD0
Boot001B* USB HDD
Boot001C* PCI LAN
Boot001D* IDER BOOT CDROM
Boot001E* IDER BOOT Floppy
Boot001F* ATA HDD
Boot0020* ATAPI CD
Boot0021* PCI LAN

¹Note: you need to have aproriate rights to run efibootmgr. You may have to use su -c 'efbootmgr' or sudo efibootmgr to gain these rights.


When using the -v (--verbose) option, we get a more detialed overview:

# efibootmgr --verbose
BootCurrent: 0002
Timeout: 2 seconds
BootOrder: 0002,0017,0018,0019,001A,001B,001C,0021,0003
Boot0002* gentoo        HD(2,GPT,ef123e3c-e202-993b-9357-67b491def4cc,0x1800,0x40000)/File(\EFI\gentoo\grubx64.efi)
Boot0003* Linux-Firmware-Updater        HD(2,GPT,ef123e3c-e202-993b-9357-67b491def4cc,0x1800,0x40000)/File(\EFI\gentoo\fwupdx64.efi)
Boot0010  Setup FvFile(ef123e3c-e202-993b-9357-67b491def4cc)
Boot0011  Boot Menu     FvFile(ef123e3c-e202-993b-9357-67b491def4cc)
Boot0012  Diagnostic Splash Screen      FvFile(ef123e3c-e202-993b-9357-67b491def4cc)
Boot0013  Lenovo Diagnostics    FvFile(ef123e3c-e202-993b-9357-67b491def4cc)
Boot0014  Startup Interrupt Menu        FvFile(ef123e3c-e202-993b-9357-67b491def4cc)
Boot0015  Rescue and Recovery   FvFile(ef123e3c-e202-993b-9357-67b491def4cc)
Boot0016  MEBx Hot Key  FvFile(ef123e3c-e202-993b-9357-67b491def4cc)
Boot0017* USB CD        VenMsg(ef123e3c-e202-993b-9357-67b491def4cc,12345678901234567890123456789012)
Boot0018* USB FDD       VenMsg(ef123e3c-e202-993b-9357-67b491def4cc,12345678901234567890123456789012)
Boot0019* NVMe0 VenMsg(ef123e3c-e202-993b-9357-67b491def4cc,12345678901234567890123456789012)
Boot001A* ATA HDD0      VenMsg(ef123e3c-e202-993b-9357-67b491def4cc,12345678901234567890123456789012)
Boot001B* USB HDD       VenMsg(ef123e3c-e202-993b-9357-67b491def4cc,12345678901234567890123456789012)
Boot001C* PCI LAN       VenMsg(ef123e3c-e202-993b-9357-67b491def4cc,12345678901234567890123456789012)
Boot001D* IDER BOOT CDROM       PciRoot(0x0)/Pci(0x16,0x2)/Ata(0,1,0)
Boot001E* IDER BOOT Floppy      PciRoot(0x0)/Pci(0x16,0x2)/Ata(0,0,0)
Boot001F* ATA HDD       VenMsg(ef123e3c-e202-993b-9357-67b491def4cc,12345678901234567890123456789012)
Boot0020* ATAPI CD      VenMsg(ef123e3c-e202-993b-9357-67b491def4cc,12345678901234567890123456789012)
Boot0021* PCI LAN       VenMsg(ef123e3c-e202-993b-9357-67b491def4cc,12345678901234567890123456789012)

Delete entries

As you can see in the examples above, I deleted the two first entries Boot0001 and Boot0000.
I did this by running efbootmgr -B -b 0000 and efibootmgr -B -b 0001 :)
According to efibootmgr --help the two options I’m using are:
-B | --delete-bootnum delete bootnum
to say that I want to delete a boot entry. And:
-b | --bootnum XXXX modify BootXXXX (hex)
to say which one I want to erase.
This felt pretty straight forward to me…

Create new entries

To create an entry you would use options similar to these:
efibootmgr --create --part 2 --disk /dev/nvme0n1p2 --loader "\EFI\gentoo\grub64.efi" --label "test-entry"
The commandline options used are:
-c | --create create new variable bootnum and add to bootorder
to say that we want to create a new entry,
-p | --part part (defaults to 1) containing loader
to define number of the partition the .efi file is located,
-d | --disk disk (defaults to /dev/sda) containing loader
to tell the device containing the .efi file,
-l | --loader name (defaults to "\EFI\Gentoo\grub.efi")
to set the path where the .efi file is located, and finaly
-L | --label label Boot manager display label (defaults to "Linux")
to set a label for the entry.

Miscellaneous

There are a lot of neat other options like setting the timeout:
-t | --timeout seconds set boot manager timeout waiting for user input.
or even deleting it:
-T | --delete-timeout delete Timeout.
You can clean up your BootOrder by deleting duplicates:
-D | --remove-dups remove duplicate values from BootOrder
or set a new BootOrder:
-o | --bootorder XXXX,YYYY,ZZZZ,... explicitly set BootOrder (hex)
you are able to set the BootNext parameter to try a certain bootentry once and lots of other cool stuff :)

Conclusion

I think efibootmgr is a great and handy tool which is worth sharing with you. :)
Of course given that you are able to use it – have the kernel options compiled or the module loaded.

Firmware Drivers  --->
   EFI (Extensible Firmware Interface) Support  --->
       <*> EFI Variable Support via sysfs