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I have been confronted with this GUI:

enter image description here

There is a question about that here, and trying to provide an answer in order to avoid any confusion for a beginner, I simply ended up asking myself whether that installer setting could be confusing by itself (I mean the result of a confusion in design).

No matter the selection made there only one partition is created, even if "logical" is the one selected: the system is installed on a logical partition that fills an entire extended partition. The installer not only tell us nothing about extended partitions (we are supposed to know that "logical" necessarily means an extended partition there too), and no extended-logical structure is displayed in the graphical scheme we see there, but we are never asked if we want more than one logical partition.

I'm not sure in what Ubuntu version that GUI is present with exactly that options, and I am not confronted with this situation as I write this, I have just been remembered by the other question (that I was trying to answer) the multiple times when I have found myself with a system installed on an extended partition (that is, a logical one that fills an entire extended one).

The fact that the installer doesn't ask if we want more than one logical partition within that extended one, and simply creates one logical that fills the entire extended partition is confusing. What could be the use of that?

Isn't a logical partition (meaning also an extended one) serving a purpose only if we want more than one of that kind? What could be the use of an extended partition with only one logical? Shouldn't the choice be between a logical and an extended partition? And if the second was to be selected, shouldn't there be a new choice regarding the number of logical partitions?

As things are, the "logical" option results in a pointless scenario.

Oh, and furthermore: that is the default option! Even if this choice was justified, "primary" should be the default (already selected) option.

As the answer to the linked question says, "it does not matter much" logical or primary. I didn't gave it much attention myself, and realized I had useless (one-logical) extended partitions on my drive only when I opened a partition manager at a later time. But I ended up with a confusing image about these matters.

cipricus
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    Have you tried to create multiple logical partitions? Or some primary and some logical ones? If you think the installer contains a misconception which should be corrected, please check How do I report a bug? – Melebius Feb 03 '20 at 11:08
  • @Melebius - I have done a lot of partitioning, but I do that with a partition manager before launching the installer. So, I don't bother to partition with the installer and leave the default option. Only recently have I noticed that gives me an one-logical extended partition. I was asking maybe that serves some purpose. I am not sure that there is a misconception (that was rhetoric, I doubt that - I'm just a user, far from the IT field). – cipricus Feb 03 '20 at 11:30
  • Obsolete with gpt (GUID) partitioning. It still shows but is not used with gpt. And UEFI/gpt has been standard since Windows 8 released in 2012. If using Windows in MBR mode then you will have BIOS/MBR. The rules on partitions is that you can only have 4 primary partitions. Or one primary can be the extended and then an unlimited number of logical inside the extended. You can only have one extended or all logical partitions must be adjacent to each other so the extended can include them. If using only Ubuntu on a drive in BIOS mode you also use gpt, I started using gpt in 2010 with Ubuntu. – oldfred Feb 03 '20 at 14:37
  • Please see if you can help with this question? – DK Bose Feb 06 '20 at 02:07
  • Status please... – heynnema Mar 03 '20 at 01:33

2 Answers2

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It breaks down to this...

Older computers have a BIOS, and use MBR disk partioning on the hard disk.

  • MBR partitioning only allows a maximum of 4 disk partitions
  • normally that translates to 3 primary partitions, and 1 extended partition that contains various logical partitions.

Newer computers have a UEFI system, and use GPT disk partioning on the hard disk.

  • GPT partitioning has no such partition limits, and normally only uses primary partitions.

When installing Ubuntu, you don't have to decide how to partition your hard disk, as Ubuntu will do that for you. Especially when using a small hard disk, or only one hard disk, there's really NO NORMAL REASON to manually partition the drive.

Update #1:

You're partially correct. Having an extended partition with only one logical partition doesn't make a whole lot of sense... as long as it has only one logical partition... but that's NOT normally the case.

Three more common scenarios end up with more logical partitions...

  1. Where the user has to create a logical swap partition for hibernation.

  2. Where the user has decided to have a separate / root partition, and a separate /home partition.

  3. Where the user has an extended partition, with only one logical partition, and later wishes to add additional logical partitions.

Also remember that fresh installs of current versions of Ubuntu prefer a /swapfile, unless it finds a prior swap partition.

heynnema
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  • I don't see in what way this addresses the question. I have multiple partitions, system ones (Windows and Linux) and non-system ones, on MBR, and when installing I format partitions myself. I also know about the limitations on MBR. But that's not my point. I just see that selecting "logical" in that GUI we get a system installed in a logical partition filling an entire extended one, which I consider pointless. What I ask is if I'm wrong or not when I say that is pointless, that the GUI is in this respect "buggy". – cipricus Mar 03 '20 at 13:11
  • I have edited the title to make it more up to the point. – cipricus Mar 03 '20 at 13:21
  • @cipricus I think that you're over-thinking all of this... one extended partition that contains only one logical partition is NOT pointless... however, please see the update in my answer. – heynnema Mar 03 '20 at 14:29
  • @cipricus I can't speak to "other" installers from a question from 2012, but current Ubuntu installers can multi-partition an extended partition. This question only applies to MBR disks, which are very much in the minority now a days. – heynnema Mar 03 '20 at 14:47
  • Maybe I am getting it: the installer GUI had the partition-size option, which means probably that creating a logical partition smaller than the whole space would have resulted in an extended one filling that space but in a logical one that left space for more than one. – cipricus Mar 03 '20 at 14:48
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After try, I found that ubuntu 20 will using gpt as default. In gpt partition, there is no difference between primary and logic partition:

$ sudo parted /dev/sdd
Partition Table: gpt
Disk Flags:

Number  Start   End     Size    File system  Name                  Flags
 1      1049kB  2097kB  1049kB                                     bios_grub
 2      2097kB  540MB   538MB   fat32        EFI System Partition  boot, esp
 3      540MB   7540MB  7000MB  ext4
 4      7540MB  7551MB  10.5MB  ext4
 5      7551MB  7561MB  10.5MB  ext4
 6      7561MB  7572MB  10.5MB  ext4
 7      7572MB  7582MB  10.5MB  ext4
 8      7582MB  7602MB  19.9MB  ext4
 9      7602MB  7622MB  19.9MB  ext4
10      7622MB  7642MB  19.9MB  ext4
11      7642MB  7662MB  19.9MB  ext4

In above result, 20MB is logic partition, 10MB is primary partition

And if you install on a mbr disk, if you want to have more than 4 partition, you must use logic partition. For the partition after fourth, even you choose primary, it still a logic partition, above 10MB is primary partition.

$ sudo parted /dev/sda
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type      File system  Flags
 1      1049kB  1000MB  999MB   primary   fat32        boot, esp
 2      1000MB  8001MB  7000MB  primary   ext4
 3      8001MB  8011MB  10.5MB  primary   ext4
 4      8012MB  8081MB  69.2MB  extended
 5      8012MB  8031MB  18.9MB  logical   ext4
 6      8032MB  8051MB  18.9MB  logical   ext4
 7      8052MB  8071MB  18.9MB  logical   ext4
 8      8072MB  8081MB  9437kB  logical   ext4
Phantom
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  • This is incorrect. There are no logical partitions in your GPT example. In GPT there are (typically) multiple primary partitions. In MBR there are (typically three) primary partitions, and (usually one) extended partition which contain (typically) more than one logical partition. Look at this using Disks or gparted to see this graphically. – heynnema Jan 16 '21 at 15:23