How does the /boot/ and /efi partitions work?

AspieHacker · n00b Joined: 10 Apr 2017 Posts: 2 Location: Iowa

Okay so I have been working on my gentoo installation for about a week now and I am finally at the installing the bootloader stage. I am getting really confused about how the /boot partition and the /efi partition work so could someone please help me understand what is going on here thank you. I would like to apologize for the lack of complete sentences, but I think in lots of abstract pictures so sentences can be somewhat hard for me to form, down below is some information on what I have done and hopefully a little more helpful.

What I had first

/dev/sda1 grub bios_grub 1mib to 3mib
/dev/sda2 /boot ext2 boot boot, esp 3mib to 131mib
/dev/sda3 none swap swap 131mib to 643mib
/dev/sda4 / ext4 rootfs 643mib to 228932mib
out of 457863mib

What I changed it to

/dev/sda1 /boot vfat boot boot, esp 3mib to 131mib
/dev/sda2 none swap swap 131mib to 643mib
/dev/sda3 / ext4 rootfs 643mib to 228932mib
out of 457863mib

What I'm wondering?

How should /efi be attached to the system?

Like this?

/dev/sda1=/efi
/dev/sda2=/boot
/dev/sda3=/swap
/dev/sda4=/root

(/root/)
/mnt/gentoo/boot/efi
where /efi is attach to sda1 and mounted to /sda2 (/boot)

or like this?

/dev/sda2=/boot /efi is like an extended partition of boot
/dev/sda3=/swap
/dev/sda4=/root

(/root/)
/mnt/gentoo/boot/efi

or would it be like /proc/?

These are just some things I am wondering and I would just like to understand what is going on here? So please comment if you think you can help. Also I know I probably left some information out so if I did just ask thank you.

Logicien · Posted: Tue Apr 11, 2017 6:39 pm Post subject:

You can use only one partition for both boot and efi. This partition must have the Efi System ID, be formated in Fat and must cover the size of the boot and efi data who will go there. You mount this partition in the /boot directory of the root partition and it will have a double purpose.

By default, the boot partition is mounted in the /boot directory and the efi one in /boot/efi, all from the root directory /.
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AspieHacker · n00b Joined: 10 Apr 2017 Posts: 2 Location: Iowa

Okay I think I know what is happening I am getting partitions and directories mixed up with each other. So this might seem kind of basic to you down below, but I am just trying to fit the details together so I can understand this better.

Directories

root (/mnt/gentoo)
boot
efi
swap
proc
sys
dev

Partitions

/dev/sda1
/dev/sda2
/dev/sda3

/dev/sda3 mounts on to /mnt/gentoo
which is essentially an empty box

which makes the directories /boot, /swap, /proc, /sys, and /dev
boxes within /mnt/gentoo

which therefore would make the efi directory a box within /boot within /mnt/gentoo.

So /dev/sda1 will be mounted onto two places on the file system. Through /boot
and /efi. Okay I think I got it now thank you for the help. If I am wrong about anything just tell me thanks again.

Roman_Gruber · Posted: Wed Apr 12, 2017 1:57 pm Post subject:

Hu · Moderator Joined: 06 Mar 2007 Posts: 21631

In most cases, no explicit swap file/directory is necessary. Swap is required for hibernation. OP has not told us the age of the system nor its RAM size, so we cannot know whether he has sufficient RAM that swap will be unnecessary for daily usage.

Fitzcarraldo · Posted: Thu Apr 13, 2017 11:53 am Post subject:

Yes, there are many factors and variables. A couple of weeks ago I was working on some very large spreadsheets on my old Compal NBLB2 laptop which had 4GB RAM and 4GB swap partition. Half or more of the swap partition was being used. So I increased the laptop's RAM to 8GB and swap is no longer being used.
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DONAHUE · Posted: Thu Apr 13, 2017 2:42 pm Post subject:

if you are to use UEFI you must have an EFI System Partition (ESP) formatted in a vfat file system (for maximum probability of motherboard compatibility in FAT32). The only time the ESP needs to be attached to the file system is when some change is to be made to the ESP. The ESP may be mounted to any convenient directory (mount point) in the file system. In various documents in the gentoo wiki; /boot, /boot/efi, /boot/EFI, /mnt/efi, and /mnt/EFI . If my memory serves, / is also recommended somewhere. Limitations: you need to know where you mounted it before you can change anything on the ESP. If the file structure of the ESP is non standard as results from using the gentoo handbook you will need to know/determine the structure (standard first directory is \EFI in the uefi spec, /boot in the handbook).
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Fitzcarraldo · Posted: Thu Apr 13, 2017 4:56 pm Post subject:

steveL · Posted: Sat Apr 15, 2017 5:50 pm Post subject:

AspieHacker, you already have a merged /boot and ESP, so there is no need to "attach /efi" anywhere.
It's a little small, but you seem to be installed (grub takes quite a lot of space in /boot/grub, mind.)

If you did have a separate (FAT32) ESP and (eg ext2) /boot, then you would attach the ESP at /boot/efi.
But you don't, so don't worry about it.

(You can only separate now, by repartitioning, which isn't worth it. It would mean reinstalling.)

Simply adjust paths you see (in documentation) under /boot/efi/EFI to use /boot/EFI instead.