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I have a CentOS 7 Virtual Machine (VM). I add a new disk to a VM with VMware workstation. Then on the guest CentOS VM, I run the fdisk command, to start adding the partitions that I want. After I specify p to add a primary partition, I see output like follows:

Partition number (1-4): 1 First cylinder (1-47536, default 1): Using default value 1 Last cylinder or +size or +sizeM or +sizeK (1-47536, default 47536): Using default value 47536

My question relates to the 1st line of italic text above. Why does it say (1-4)? Are you not allowed to have more than 4 partitions on a single disk?

  • Pretty simple to answer with web search... – jc__ Jul 13 '17 at 17:19
  • What would a root partition be considered, a primary partition? How about a swap partition and convenience partitions like /boot, /home, /usr, /opt, /tmp, /usr/src, are these extended partitions? – wesg Jul 13 '17 at 17:31
  • Read the section "MBR Partitions" in this PDF. These are partitions on disk "a": sda1 sda2. These are partations on disk "b": sdb1 sdb3. The directories or mount points you listed like root /; /boot; /usr; /tmp may be all on the same disk partition /sda1 or multiple disk partitions /sda6. The disk partitions can be primary, extended or logical, so the mount point /tmp does not determine the partition type. – jc__ Jul 13 '17 at 18:00
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That's correct. You're only allowed 4 primary partitions. And you typically use one of those 4 to create an "extended" partition, which contains partitions 5 and up (the logical partitions). You can many logical partitions.

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You are only allowed to have 4 primary partitions. It has been that way since 1981. The reason is that the standard Master Boot record only has room for a partition table containing four entries.

Extended partitions are created by using a rather tortuous chaining of boot records in the actual partitions. That number is theoretically not limited, although if used on DOS/Windows you would soon run out of drive letters!

Another option is to use a GPT based solution - this replaces the Master Boot Record. But for now, once you've created a primary partition, fdisk will allow you to do other things. How many partitions do you want?

  • Thank you for feedback, have details on the comment I posted below original question? I'm not sure if your familiar with this site, but I was running through direction for Linux From Scratch (LFS) at linuxfromscratch.org/lfs/view/stable/chapter02/… – wesg Jul 13 '17 at 17:36

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