Fresh installation of 20.04 makes three partitions – right?

Now to get to the bottom of my problems mentioned in another thread, I decided to install 20.04 anew. In order to not produce problems from the start on, I let the installation program do as it wished and use the whole disc.

It then left me with three partitions: sda1, 537MB in /boot/efi; sda2, 240GB Format Extended and not mounted; and sda5, 240GB, Format Linux and mounted at "/".

First question, is that the way this is normally done? My Disc even if it has 500GB is named "240GB Disc". Can I mount and access sda2 at all? Is there some special function it’s used for?

Thanks for any help. I’m scared of setting this machine up in a way that’s stupid.

Festplatte /dev/loop0: 4 KiB, 4096 Bytes, 8 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop1: 61,98 MiB, 64966656 Bytes, 126888 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop2: 346,3 MiB, 363118592 Bytes, 709216 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop3: 91,7 MiB, 96141312 Bytes, 187776 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop4: 54,24 MiB, 56872960 Bytes, 111080 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/loop5: 46,98 MiB, 49242112 Bytes, 96176 Sektoren
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes


Festplatte /dev/sda: 223,58 GiB, 240057409536 Bytes, 468862128 Sektoren
Festplattenmodell: CT240BX500SSD1  
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes
Festplattenbezeichnungstyp: dos
Festplattenbezeichner: 0x853c4b3c

Gerät      Boot  Anfang      Ende  Sektoren  Größe Kn Typ
/dev/sda1  *       2048   1050623   1048576   512M  b W95 FAT32
/dev/sda2       1052670 468860927 467808258 223,1G  5 Erweiterte
/dev/sda5       1052672 468860927 467808256 223,1G 83 Linux
Asked By: ClausRogge

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MBR vs GPT

It looks like your hard disk was set up with a Master Boot Record (MBR). This is the older type of partition tables. More recent hard disk drives (HDD) and solid state drives (SSD) use GUID Partition Table (GPT). See What’s the Difference Between GPT and MBR When Partitioning a Drive? for more on MBR and GPT.

When MBR was designed, hard drives used to be relatively small. Like many things designed in the early days of computers the designers of MBR thought one would never need more than 4 partitions in a disk drive. Thus, one of the limitation of MBR is that it can have only 4 (primary) partitions.

GPT does not have this limitation.

Primary > Extended > Logical

An extended partition in a MBR is a special primary partition that holds one or more logical partitions. In your case, /dev/sda2 is an extended partition. Inside /dev/sda2 there is a logical partition: /dev/sda5.

Note, in MBR primary (and extended) partitions are numbered 1,2,3,4. Logical partitions start at 5.

See Hard Disk Partitions Explained for more on partitions.

Default Ubuntu Installation

When the Ubuntu installer finds a disk with MBR, it creates an extended partition and inside it a logical partition to install Ubuntu. This is mainly allow Windows to coexist with Ubuntu.

In the olden days Ubuntu installation used to create a separate swap partition along with the system partition (/). This would not be possible without using extended and logical partitions in a MBR dual boot system with Windows using up 3 primary partitions.

By the way, recent versions of Windows require GPT to install in the UEFI mode. (I don’t think Windows 11 can be installed in a MBR disk.) Ubuntu does not have that requirement.

Questions:

First question, is that the way this is normally done?

This is normal for MBR type partition tables.

My Disc even if it has 500GB is named "240GB Disc".

I can’t answer this.

Can I mount and access sda2 at all?

No. As I explained above, /dev/sda2 is an extended partition.

Is there some special function it’s used for?

The only use of an extended partition is a container for one or more logical partition. In your case it contains the logical partition /dev/sda5.

Hope this helps

Answered By: user68186
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