When using fdisk, how do I find what partition numbers are already in use?

Question

When I create a new partition with fdisk, I am asked to choose a number for the new partition (1 through 4). Is this number the same as the integer value for "ID" when I use fdisk -l ? If so, why are some greater than 4? If not, what command do I use to view the partiion numbers that are available to me? What is the consequence of just choosing 1 for two or more partitions? I know that this can work (at least, it seems to work without problems).

Solution

The partition number do you talking about is the number of a primary partition. You can have only four per device and you can't use the same partition number twice.

To list the partition number use, e.g

sudo fdisk /dev/sda

or (for an example see below))

sudo parted /dev/sda print

You should see something like this

% sudo fdisk /dev/sdb

Welcome to fdisk (util-linux 2.26.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/sdb: 7,5 GiB, 8019509248 bytes, 15663104 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc3072e18

Device     Boot Start      End  Sectors  Size Id Type
/dev/sdb1          62 15650907 15650846  7,5G 83 Linux

This means, I have one primary partition. The next primary partition would be 2, 3, 4. This

/dev/sdb1

and this

/dev/sdb5

means, you have one primary partition sda1 and one logical partition sdb5. You can only create logical partitions inside a primary partition.

---

To show the partition types you could use

sudo parted /dev/sda print

Output could be

Disk /dev/sda: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number  Start   End    Size    Type      File system  Flags
 1      1049kB  105GB  105GB   primary   ntfs         boot
 2      105GB   205GB  100GB   primary   ext3
 3      205GB   207GB  1999MB  primary   linux-swap
 4      207GB   500GB  293GB   extended               lba
 5      207GB   500GB  293GB   logical   ntfs

Means sda4 is a primary partition now called extended partition, with one logical partition.

---

The partition number isn't the same number as the ID. The ID is the ID for the type of the partition:

 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           bc  Acronis FAT32 L ff  BBT            
1e  Hidden W95 FAT1 80  Old Minix       be  Solaris boot

Comments

[Terrance]

I was going to post a comment about being allowed only 4 primary partitions in the dos partition scheme, but you beat me to it. =) +1