Partitions, GPT, and MBR · Linux

The partition table is the first structure on a disk. It tells the firmware and the kernel where each partition starts and ends. A Linux host cannot boot without a valid partition table on the boot disk.

MBR vs GPT

Two partition table formats are in production today. They are not compatible.

	MBR	GPT
Max disk size	2 TiB	8 ZiB
Max partitions	4 primary (or 3 + extended)	128
Backup header	No	Yes (end of disk)
CRC	No	Yes
Modern host	No (legacy)	Yes (default)

Read-only / Safefdisk -l— fdisk -l reads the partition table. Disklabel type: gpt confirms a GPT. The EFI System partition is the UEFI System Partition (ESP); the Linux filesystem is the rest of the disk.

$ fdisk -l /dev/sda

Disk /dev/sda: 100 GiB, 107374182400 bytes, 209715200 sectors
Units: sectors of 1 * 512 = 512 bytes
Disklabel type: gpt
Device       Start      End  Sectors  Size Type
/dev/sda1     2048   2099199  2097152    1G EFI System
/dev/sda2  2099200 209715166 207615967 99G Linux filesystem

Inspecting partitions

Read-only / Safegdisk -l— gdisk shows the GPT with partition type codes. EF00 is EFI System Partition, 8300 is Linux filesystem. These type codes help the firmware and the kernel understand the partition purpose.

$ gdisk -l /dev/sda

GPT fdisk (gdisk) version 1.0.9
Partition table scan:
MBR: protective
BSD: not present
APM: not present
GPT: present
Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 209715200 sectors, 100.0 GiB
Number  Start (sector)  End (sector)  Size     Code  Name
1            2048        2099199   1024.0 MiB  EF00  EFI System
2         2099200      209715166  99.0 GiB    8300  Linux filesystem

Creating a partition scheme

For a new disk, the standard production layout is:

Create a GPT partition table with parted or gdisk
Create partition 1 as the EFI System Partition (at least 512 MB, FAT32)
Create partition 2 as a Linux filesystem (ext4 or xfs, rest of the disk)
Or create partition 2 as an LVM physical volume for flexible storage
Write the partition table and verify with fdisk -l
Create the filesystem with mkfs.ext4 or mkfs.xfs
Mount with a UUID in /etc/fstab; verify with mount -a

Partition types and codes

Read-only / Safepartition type codes— Common GPT partition type codes: EF00 EFI System Partition, 8300 Linux filesystem, 8E00 Linux LVM, 8200 Linux swap. The codes tell the firmware and the kernel what each partition is for.

$ gdisk -l /dev/sda 2>/dev/null | grep -E '^\\s+[0-9]+'

1 2048 2099199 1024.0 MiB EF00 EFI System
2 2099200 209715166 99.0 GiB 8300 Linux filesystem