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Setting a partition's type to ef02 is easy in gdisk. You just type it. However, I could not find a similar type code in fdisk. I don't want to use gdisk, because it force convert my drive to GPT which I do not want.

FYI, fdisk’s (util-linux 2.20.1) options for partition type break down as follows:

 0  Empty           24  NEC DOS         81  Minix / old Lin bf  Solaris        
 1  FAT12           27  Hidden NTFS Win 82  Linux swap / So c1  DRDOS/sec (FAT-
 2  XENIX root      39  Plan 9          83  Linux           c4  DRDOS/sec (FAT-
 3  XENIX usr       3c  PartitionMagic  84  OS/2 hidden C:  c6  DRDOS/sec (FAT-
 4  FAT16 <32M      40  Venix 80286     85  Linux extended  c7  Syrinx         
 5  Extended        41  PPC PReP Boot   86  NTFS volume set da  Non-FS data    
 6  FAT16           42  SFS             87  NTFS volume set db  CP/M / CTOS / .
 7  HPFS/NTFS/exFAT 4d  QNX4.x          88  Linux plaintext de  Dell Utility   
 8  AIX             4e  QNX4.x 2nd part 8e  Linux LVM       df  BootIt         
 9  AIX bootable    4f  QNX4.x 3rd part 93  Amoeba          e1  DOS access     
 a  OS/2 Boot Manag 50  OnTrack DM      94  Amoeba BBT      e3  DOS R/O        
 b  W95 FAT32       51  OnTrack DM6 Aux 9f  BSD/OS          e4  SpeedStor      
 c  W95 FAT32 (LBA) 52  CP/M            a0  IBM Thinkpad hi eb  BeOS fs        
 e  W95 FAT16 (LBA) 53  OnTrack DM6 Aux a5  FreeBSD         ee  GPT            
 f  W95 Ext'd (LBA) 54  OnTrackDM6      a6  OpenBSD         ef  EFI (FAT-12/16/
10  OPUS            55  EZ-Drive        a7  NeXTSTEP        f0  Linux/PA-RISC b
11  Hidden FAT12    56  Golden Bow      a8  Darwin UFS      f1  SpeedStor      
12  Compaq diagnost 5c  Priam Edisk     a9  NetBSD          f4  SpeedStor      
14  Hidden FAT16 <3 61  SpeedStor       ab  Darwin boot     f2  DOS secondary  
16  Hidden FAT16    63  GNU HURD or Sys af  HFS / HFS+      fb  VMware VMFS    
17  Hidden HPFS/NTF 64  Novell Netware  b7  BSDI fs         fc  VMware VMKCORE 
18  AST SmartSleep  65  Novell Netware  b8  BSDI swap       fd  Linux raid auto
1b  Hidden W95 FAT3 70  DiskSecure Mult bb  Boot Wizard hid fe  LANstep        
1c  Hidden W95 FAT3 75  PC/IX           be  Solaris boot    ff  BBT            
1e  Hidden W95 FAT1 80  Old Minix 

Where is ef02 in this list and which alternative should I use?

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    As far as I can tell, type ef02 is thé BIOS boot partition, which translates to a specific GUID in GPT. I don't see what it would be on a non GPT disk, which may be why fdisk doesn't offer it. Sep 20, 2015 at 5:50

1 Answer 1

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user2313067 is absolutely correct. What gdisk refers to as EF02 is shorthand for a GUID of 21686148-6449-6E6F-744E-656564454649 -- that is, it identifies a BIOS Boot Partition. There is no equivalent partition type code for MBR.

To elaborate further, the GRUB bootloader, when installed in BIOS mode on an MBR disk, stores part of itself in the MBR, part of itself in the sectors between the MBR and the first partition, and part of itself in files on a partition that you specify (normally in the /boot/grub or /boot/grub2 directory in Linux). The post-MBR sectors are officially unallocated, so GRUB storing part of itself there is potentially a bit risky, but it usually works fine. Under GPT, the sectors immediately following the MBR are used by the GPT data structures themselves; and prior to the release of Advanced Format disks, it was common for the first partition to begin on the sector immediately following those data structures. In other words, there is no equivalent under GPT to the (almost) safe post-MBR space. Thus, to enable BIOS-mode booting on GPT disks, GRUB's developers created the idea of a BIOS Boot Partition, where boot loader code could be stored "raw." In principle, the idea could be applied on MBR disks, too, but AFAIK nobody's done that -- at least not for GRUB. (OS/2's boot loader did have its own partition type code [0x0A], and there may be other boot loaders that do something similar.)

The bottom line is that you probably don't need to create a special partition for your purposes. That said, your question doesn't specify what you're trying to accomplish, in the end. (Creating a BIOS Boot Partition is not a goal in and of itself; presumably you want to do something like install a new OS or a new boot loader for an existing multi-boot configuration.) Depending on what your ultimate goal is, you might need to do something special.

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