Handbook:X86/Blocks/Disks/tr

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This page is a translated version of the page Handbook:X86/Blocks/Disks and the translation is 75% complete.



Although it is theoretically possible to use a raw, unpartitioned disk to house a Linux system (when creating a btrfs RAID for example), this is almost never done in practice. Instead, disk block devices are split up into smaller, more manageable block devices. On x86 systems, these are called partitions. There are currently two standard partitioning technologies in use: MBR (sometimes also called DOS disklabel) and GPT; these are tied to the two boot process types: legacy BIOS boot and UEFI.

GPT

The GUID Partition Table (GPT) setup (also called GPT disklabel) uses 64-bit identifiers for the partitions. The location in which it stores the partition information is much bigger than the 512 bytes of the MBR partition table (DOS disklabel), which means there is practically no limit on the number of partitions for a GPT disk. Also, the maximum partition size is much larger (almost 8 ZiB -- yes, zettabytes).

When a system's software interface between the operating system and firmware is UEFI (instead of BIOS), GPT is almost mandatory as compatibility issues will arise with DOS disklabel.

GPT also takes advantage of checksumming and redundancy. It carries CRC32 checksums to detect errors in the header and partition tables and has a backup GPT at the end of the disk. This backup table can be used to recover damage of the primary GPT near the beginning of the disk.

Önemli
There are a few caveats regarding GPT:
  • Using GPT on a BIOS-based computer works, but then one cannot dual-boot with a Microsoft Windows operating system. The reason is that Microsoft Windows will boot in UEFI mode if it detects a GPT partition label.
  • Some buggy (old) motherboard firmware configured to boot in BIOS/CSM/legacy mode might also have problems with booting from GPT labeled disks.

Master boot record (MBR) or DOS boot sector

The Master boot record boot sector (also called DOS boot sector, DOS disklabel, and - more recently, in contrast to GPT/UEFI setups - legacy BIOS boot) was first introduced in 1983 with PC DOS 2.x. MBR uses 32-bit identifiers for the start sector and length of the partitions, and supports three partition types: primary, extended, and logical. Primary partitions have their information stored in the master boot record itself - a very small (usually 512 bytes) location at the very beginning of a disk. Due to this small space, only four primary partitions are supported (for instance, /dev/sda1 to /dev/sda4).

In order to support more partitions, one of the primary partitions in the MBR can be marked as an extended partition. This partition can then contain additional logical partitions (partitions within a partition).

Önemli
Although still supported by most motherboard manufacturers, MBR boot sectors and their associated partitioning limitations are considered legacy. Unless working with hardware that is pre-2010, it best to partition a disk with GUID Partition Table. Readers who must proceed with setup type should knowingly acknowledge the following information:
  • Most post-2010 motherboards consider using MBR boot sectors a legacy (supported, but not ideal) boot mode.
  • Due to using 32-bit identifiers, partition tables in the MBR cannot address storage space that is larger than 2 TiBs in size.
  • Unless an extended partition is created, MBR supports a maximum of four partitions.
  • This setup does not provide a backup boot sector, so if something overwrites the partition table, all partition information will be lost.
That said, MBR and legacy BIOS boot may still used in virtualized cloud environments such as AWS.

The Handbook authors suggest using GPT whenever possible for Gentoo installations.

Advanced storage

The official Gentoo boot media provides support for Logical Volume Manager (LVM). LVM can combine physical volumes such as partitions or disks into volume groups. Volume groups are more flexible than partitions and can be used to define RAID groups or caches on fast SSDs for slow HDs. Although usage is not covered in the handbook, LVM is fully supported in Gentoo.

Default partitioning scheme

Throughout the remainder of the handbook, we will discuss and explain two cases:

  1. UEFI firmware with GUID Partition Table (GPT) disk.
  2. MBR DOS/legacy BIOS firmware with a MBR partition table disk.

While it is possible to mix and match boot types with certain motherboard firmware, mixing goes beyond the intention of the handbook. As previously stated, it is strongly recommended for installations on modern hardware to use UEFI boot with a GPT disklabel disk.

The following partitioning scheme will be used as a simple example layout.

Önemli
The first row of the following table contains exclusive information for either a GPT disklabel or a MBR DOS/legacy BIOS disklabel. When in doubt, proceed with GPT, since x86 machines manufactured after the year 2010 generally support UEFI firmware and GPT boot sector.
Partition Filesystem Size Description
/dev/sda1 fat32 File system required for the EFI System Partition, which is always associated with a GPT disklabel. 1 GiB EFI System Partition details. Applicable to system firmware supporting an UEFI implementation. This is typically the case for systems manufactured around the year 2010 to the present.
ext4 Recommended file system for the boot partition of a MBR partition table, which is used in conjunction with older firmware limited to the DOS/legacy BIOS disklabel. MBR DOS/legacy BIOS boot partition details. Applicable to legacy BIOS machine firmware. Systems of this type were typically manufactured <u>before</u> the year 2010 and have generally phased out of production.
/dev/sda2 linux-swap RAM size * 2 Swap partition details.
/dev/sda3 xfs Remainder of the disk The selected profile, additional partitions (optional), and system purpose add complexities for appropriately sizing the rootfs, therefore the Handbook authors cannot offer a 'one-size-fits-all' suggestion for the rootfs partition.</br></br> When Gentoo is the only operating system using the disk, selecting the remainder of the disk is the safest and suggested choice. Root partition details.

If this suffices as information, the advanced reader can directly skip ahead to the actual partitioning.

Both fdisk and parted are partitioning utilities included within the official Gentoo live image environments. fdisk is well known, stable, and handles both MBR and GPT disks. parted was one of the first Linux block device management utilities to support GPT partitions. It can be used as an alternative to fdisk if the reader prefers, however the handbook will only provide instructions for fdisk, since since it is commonly available on most Linux environments.

Before going to the creation instructions, the first set of sections will describe in more detail how partitioning schemes can be created and mention some common pitfalls.

Designing a partition scheme

How many partitions and how big?

The design of disk partition layout is highly dependent on the demands of the system and the file system(s) applied to the device. If there are lots of users, then it is advised to have /home on a separate partition which will increase security and make backups and other types of maintenance easier. If Gentoo is being installed to perform as a mail server, then /var should be a separate partition as all mails are stored inside the /var directory. Game servers may have a separate /opt partition since most gaming server software is installed therein. The reason for these recommendations is similar to the /home directory: security, backups, and maintenance.

In most situations on Gentoo, /usr and /var should be kept relatively large in size. /usr hosts the majority of applications available on the system and the Linux kernel sources (under /usr/src). By default, /var hosts the Gentoo ebuild repository (located at /var/db/repos/gentoo) which, depending on the file system, generally consumes around 650 MiB of disk space. This space estimate excludes the /var/cache/distfiles and /var/cache/binpkgs directories, which will gradually fill with source files and (optionally) binary packages respectively as they are added to the system.

How many partitions and how big very much depends on considering the trade-offs and choosing the best option for the circumstance. Separate partitions or volumes have the following advantages:

  • Choose the best performing filesystem for each partition or volume.
  • The entire system cannot run out of free space if one defunct tool is continuously writing files to a partition or volume.
  • If necessary, file system checks are reduced in time, as multiple checks can be done in parallel (although this advantage is realized more with multiple disks than it is with multiple partitions).
  • Security can be enhanced by mounting some partitions or volumes read-only, nosuid (setuid bits are ignored), noexec (executable bits are ignored), etc.


However, multiple partitions have certain disadvantages as well:

  • If not configured properly, the system might have lots of free space on one partition and little free space on another.
  • A separate partition for /usr/ may require the administrator to boot with an initramfs to mount the partition before other boot scripts start. Since the generation and maintenance of an initramfs is beyond the scope of this handbook, we recommend that newcomers do not use a separate partition for /usr/.
  • There is also a 15-partition limit for SCSI and SATA unless the disk uses GPT labels.
Not
Installations that intend to use systemd as the service and init system must have the /usr directory available at boot, either as part of the root filesystem or mounted via an initramfs.

What about swap space?

Recommendations for swap space size
RAM size Suspend support? Hibernation support?
2 GB or less 2 * RAM 3 * RAM
2 to 8 GB RAM amount 2 * RAM
8 to 64 GB 8 GB minimum, 16 maximum 1.5 * RAM
64 GB or greater 8 GB minimum Hibernation not recommended! Hibernation is not recommended for systems with very large amounts of memory. While possible, the entire contents of memory must be written to disk in order to successfully hibernate. Writing tens of gigabytes (or worse!) out to disk can can take a considerable amount of time, especially when rotational disks are used. It is best to suspend in this scenario.

There is no perfect value for swap space size. The purpose of the space is to provide disk storage to the kernel when internal dynamic memory (RAM) is under pressure. A swap space allows for the kernel to move memory pages that are not likely to be accessed soon to disk (swap or page-out), which will free memory in RAM for the current task. Of course, if the pages swapped to disk are suddenly needed, they will need to be put back in memory (page-in) which will take considerably longer than reading from RAM (as disks are very slow compared to internal memory).

When a system is not going to run memory intensive applications or has lots of RAM available, then it probably does not need much swap space. However do note in case of hibernation that swap space is used to store the entire contents of memory (likely on desktop and laptop systems rather than on server systems). If the system requires support for hibernation, then swap space larger than or equal to the amount of memory is necessary.

As a general rule for RAM amounts less than 4 GB, the swap space size is recommended to be twice the internal memory (RAM). For systems with multiple hard disks, it is wise to create one swap partition on each disk so that they can be utilized for parallel read/write operations. The faster a disk can swap, the faster the system will run when data in swap space must be accessed. When choosing between rotational and solid state disks, it is better for performance to put swap on the solid state hardware.

It is worth noting that swap files can be used as an alternative to swap partitions; this is mostly helpful for systems with very limited disk space.

What is the EFI System Partition (ESP)?

When installing Gentoo on a system that uses UEFI to boot the operating system (instead of BIOS) it is essential that an EFI System Partition (ESP) is created. The instructions below contain the necessary pointers to correctly handle this operation. The EFI system partition is not required when booting in BIOS/Legacy mode.

The ESP must be a FAT variant (sometimes shown as vfat on Linux systems). The official UEFI specification denotes FAT12, 16, or 32 filesystems will be recognized by the UEFI firmware, although FAT32 is recommended for the ESP. After partitioning, format the ESP accordingly:

root #mkfs.fat -F 32 /dev/sda1
Önemli
If the ESP is not formatted with a FAT variant, the system's UEFI firmware will not find the bootloader (or Linux kernel) and will most likely be unable to boot the system!

What is the BIOS boot partition?

A BIOS boot partition is a very small (1 to 2 MB) partition in which boot loaders like GRUB2 can put additional data that doesn't fit in the allocated storage. It only needed when a disk is formatted with a GPT disklabel, but the system's firmware will be booting via GRUB2 in legacy BIOS/MBR DOS boot mode. It is not required when booting in EFI/UEFI mode, and also not required when using a MBR/Legacy DOS disklabel. A BIOS boot partition will not be used in this guide.

Partitioning the disk with GPT for UEFI

The following parts explain how to create an example partition layout for a single GPT disk device which will conform to the UEFI Specification and Discoverable Partitions Specification (DPS). DPS is a specification provided as part of the Linux Userspace API (UAPI) Group Specification and is recommended, but entirely optional. The specifications are implemented using the fdisk utility, which is part of the sys-apps/util-linux package.

The table provides a recommended defaults for a trivial Gentoo installation. Additional partitions can be added according to personal preference or system design goals.

Device path (sysfs) Mount point File system DPS UUID (Type-UUID) Description
/dev/sda1 /efi vfat c12a7328-f81f-11d2-ba4b-00a0c93ec93b EFI system partition (ESP) details.
/dev/sda2 N/A. Swap is not mounted to the filesystem like a device file. 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f Swap partition details.
/dev/sda3 / xfs 44479540-f297-41b2-9af7-d131d5f0458a Root partition details.

Viewing the current partition layout

fdisk is a popular and powerful tool to split a disk into partitions. Fire up fdisk against the disk (in our example, we use /dev/sda):

root #fdisk /dev/sda

Use the p key to display the disk's current partition configuration:

Command (m for help):p
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: HGST HTS721010A9
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 3E56EE74-0571-462B-A992-9872E3855D75
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Device        Start        End    Sectors   Size Type
/dev/sda1      2048    2099199    2097152     1G EFI System
/dev/sda2   2099200   10487807    8388608     4G Linux swap
/dev/sda3  10487808 1953523711 1943035904 926.5G Linux root (x86-64)

This particular disk was configured to house two Linux filesystems (each with a corresponding partition listed as "Linux") as well as a swap partition (listed as "Linux swap").

Creating a new disklabel / removing all partitions

Pressing the g key will instantly remove all existing disk partitions and create a new GPT disklabel:

Command (m for help):g
Created a new GPT disklabel (GUID: 3E56EE74-0571-462B-A992-9872E3855D75).

Alternatively, to keep an existing GPT disklabel (see the output of p above), consider removing the existing partitions one by one from the disk. Press d to delete a partition. For instance, to delete an existing /dev/sda1:

Command (m for help):d
Partition number (1-4): 1

The partition has now been scheduled for deletion. It will no longer show up when printing the list of partitions (p, but it will not be erased until the changes have been saved. This allows users to abort the operation if a mistake was made - in that case, press q immediately and hit Enter and the partition will not be deleted.

Repeatedly press p to print out a partition listing and then press d and the number of the partition to delete it. Eventually, the partition table will be empty:

Command (m for help):p
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: HGST HTS721010A9
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 3E56EE74-0571-462B-A992-9872E3855D75

Now that the in-memory partition table is empty, we're ready to create the partitions.

Creating the EFI System Partition (ESP)

Not
A smaller ESP is possible but not recommended, especially given it may be shared with other OSes.

First create a small EFI system partition, which will also be mounted as /boot. Type n to create a new partition, followed by 1 to select the first partition. When prompted for the first sector, make sure it starts from 2048 (which may be needed for the boot loader) and hit Enter. When prompted for the last sector, type +1G to create a partition 1 GByte in size:

Command (m for help):n
Partition number (1-128, default 1): 1
First sector (2048-1953525134, default 2048):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-1953525134, default 1953523711): +1G
 
Created a new partition 1 of type 'Linux filesystem' and of size 1 GiB.
Partition #1 contains a vfat signature.
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Do you want to remove the signature? [Y]es/[N]o: Y
The signature will be removed by a write command.

Mark the partition as an EFI system partition:

Command (m for help):t
Selected partition 1
Partition type or alias (type L to list all): 1
Changed type of partition 'Linux filesystem' to 'EFI System'.

Optionally, to have the ESP conform to the Discoverable System Partition (DSP) specification, switch to expert mode and perform the following extra step to set the partition's UUID:

Command (m for help):x
Expert command (m for help):u
Selected partition 1
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New UUID (in 8-4-4-4-12 format): c12a7328-f81f-11d2-ba4b-00a0c93ec93b
Partition UUID changed from 10293DC1-DF6C-4443-8ACF-C756B81B4767 to C12A7328-F81F-11D2-BA4B-00A0C93EC93B.

Press the r key to return to the main menu:

Expert command (m for help):r
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Command (m for help):

Creating the swap partition

Next, to create the swap partition, press n to create a new partition, then press 2 to create the second partition, /dev/sda2. When prompted for the first sector, hit Enter. When prompted for the last sector, type +4G (or any other size needed for the swap space) to create a partition 4 GiB in size.

Command (m for help):n
Partition number (2-128, default 2): 
First sector (2099200-1953525134, default 2099200): 
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2099200-1953525134, default 1953523711): +4G
 
Created a new partition 2 of type 'Linux filesystem' and of size 4 GiB.

After this, press t to set the partition type, 2 to select the partition just created and then type in 19 to set the partition type to "Linux Swap".

Command (m for help):t
Partition number (1,2, default 2): 2
Partition type or alias (type L to list all): 19
 
Changed type of partition 'Linux filesystem' to 'Linux swap'.

Optionally, to have the swap partition conform to the Discoverable System Partition (DSP) specification, switch to expert mode and perform the following extra step to set the partition's UUID:

Command (m for help):x
Expert command (m for help):u
Partition number (1,2, default 2): 2
Selected partition 2
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New UUID (in 8-4-4-4-12 format): 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f
Partition UUID changed from 7529CDF6-9482-4497-B021-576745648B2A to 0657FD6D-A4AB-43C4-84E5-0933C84B4F4F..

Press the r key to return to the main menu:

Expert command (m for help):r
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Command (m for help):

Creating the root partition

Finally, to create the root partition, press n to create a new partition, and then press 3 to create the third partition: /dev/sda3. When prompted for the first sector, press Enter. When prompted for the last sector, hit Enter to create a partition that takes up the rest of the remaining space on the disk.

Command (m for help):n
Partition number (3-128, default 3): 3
First sector (10487808-1953525134, default 10487808):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (10487808-1953525134, default 1953523711):
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Created a new partition 3 of type 'Linux filesystem' and of size 926.5 GiB..
Not
Setting the root partition's type to "Linux root (x86-64)" is not required and the system will function normally if it is set to the "Linux filesystem" type. This filesystem type is only necessary for cases where a bootloader that supports it (i.e. systemd-boot) is used and a fstab file is not wanted.

After creating the root partition, press t to set the partition type, 3 to select the partition just created, and then type in 23 to set the partition type to "Linux Root (x86-64)".

Command(m for help):t
Partition number (1-3, default 3): 3
Partition type or alias (type L to list all): 23
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Changed type of partition 'Linux filesystem' to 'Linux root (x86-64)'

Optionally, to have the root partition conform to the Discoverable System Partition (DSP) specification, switch to expert mode and perform the following extra step to set the partition's UUID:

Command (m for help):x
Expert command (m for help):u
Partition number (1-3, default 3): 3
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New UUID (in 8-4-4-4-12 format): 4f68bce3-e8cd-4db1-96e7-fbcaf984b709
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Partition UUID changed from 40465382-FA2A-4846-9827-640821CC001F to 4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709.

Press the r key to return to the main menu:

Expert command (m for help):r
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Command (m for help):

After completing these steps, pressing p should display a partition table that looks similar to the following:

Command (m for help):p
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: HGST HTS721010A9
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 3E56EE74-0571-462B-A992-9872E3855D75
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Device        Start        End    Sectors   Size Type
/dev/sda1      2048    2099199    2097152     1G Linux filesystem
/dev/sda2   2099200   10487807    8388608     4G Linux swap
/dev/sda3  10487808 1953523711 1943035904 926.5G Linux root (x86-64)
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Filesystem/RAID signature on partition 1 will be wiped.

Saving the partition layout

Press w to save the partition layout and exit the fdisk utility:

Command (m for help):w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

With partitions now available, the next installation step is to fill them with filesystems.

Partitioning the disk with MBR for BIOS / legacy boot

The following table provides a recommended partition layout for a trivial MBR DOS / legacy BIOS boot installation. Additional partitions can be added according to personal preference or system design goals.

Device path (sysfs) Mount point File system DPS UUID (PARTUUID) Description
/dev/sda1 /boot ext4 N/A MBR DOS / legacy BIOS boot partition details.
/dev/sda2 N/A. Swap is not mounted to the filesystem like a device file. 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f Swap partition details.
/dev/sda3 / xfs 44479540-f297-41b2-9af7-d131d5f0458a Root partition details.

Change the partition layout according to personal preference.

Viewing the current partition layout

Fire up fdisk against the disk (in our example, we use /dev/sda):

root #fdisk /dev/sda

Use the p key to display the disk's current partition configuration:

Command (m for help):p
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: HGST HTS721010A9
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0xf163b576
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Device     Boot    Start        End    Sectors   Size Id Type
/dev/sda1  *        2048    2099199    2097152     1G 83 Linux
/dev/sda2        2099200   10487807    8388608     4G 82 Linux swap / Solaris
/dev/sda3       10487808 1953525167 1943037360 926.5G 83 Linux

This particular disk was until now configured to house two Linux filesystems (each with a corresponding partition listed as "Linux") as well as a swap partition (listed as "Linux swap"), using a GPT table.

Creating a new disklabel / removing all partitions

Pressing o will instantly remove all existing disk partitions and create a new MBR disklabel (also named DOS disklabel):

Command (m for help):o
Created a new DOS disklabel with disk identifier 0xf163b576.
The device contains 'gpt' signature and it will be removed by a write command. See fdisk(8) man page and --wipe option for more details.

Alternatively, to keep an existing DOS disklabel (see the output of p above), consider removing the existing partitions one by one from the disk. Press d to delete a partition. For instance, to delete an existing /dev/sda1:

Command (m for help):d
Partition number (1-4): 1

The partition has now been scheduled for deletion. It will no longer show up when printing the list of partitions (p, but it will not be erased until the changes have been saved. This allows users to abort the operation if a mistake was made - in that case, type q immediately and hit Enter and the partition will not be deleted.

Repeatedly press p to print out a partition listing and then press d and the number of the partition to delete it. Eventually, the partition table will be empty:

Command (m for help):p
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: HGST HTS721010A9
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0xf163b576

The disk is now ready to create new partitions.

Creating the boot partition

First, create a small partition which will be mounted as /boot. Press n to create a new partition, followed by p for a primary partition and 1 to select the first primary partition. When prompted for the first sector, make sure it starts from 2048 (which may be needed for the boot loader) and press Enter. When prompted for the last sector, type +1G to create a partition 1 GB in size:

Command (m for help):n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-1953525167, default 2048):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-1953525167, default 1953525167): +1G
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Created a new partition 1 of type 'Linux' and of size 1 GiB.

Mark the partition as bootable by pressing the a key and pressing Enter:

Command (m for help):a
Selected partition 1
The bootable flag on partition 1 is enabled now.

Note: if more than one partition is available on the disk, then the partition to be flagged as bootable will have to be selected.

Creating the swap partition

Next, to create the swap partition, press n to create a new partition, then p, then type 2 to create the second primary partition, /dev/sda2. When prompted for the first sector, press Enter. When prompted for the last sector, type +4G (or any other size needed for the swap space) to create a partition 4GB in size.

Command (m for help):n
Partition type
   p   primary (1 primary, 0 extended, 3 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (2-4, default 2): 2
First sector (2099200-1953525167, default 2099200):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2099200-1953525167, default 1953525167): +4G
 
Created a new partition 2 of type 'Linux' and of size 4 GiB.

After all this is done, press t to set the partition type, 2 to select the partition just created and then type in 82 to set the partition type to "Linux Swap".

Command (m for help):t
Partition number (1,2, default 2): 2
Hex code (type L to list all codes): 82
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Changed type of partition 'Linux' to 'Linux swap / Solaris'.

Creating the root partition

Finally, to create the root partition, press n to create a new partition. Then press p and 3 to create the third primary partition, /dev/sda3. When prompted for the first sector, hit Enter. When prompted for the last sector, hit Enter to create a partition that takes up the rest of the remaining space on the disk:

Command (m for help):n
Partition type
   p   primary (2 primary, 0 extended, 2 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (3,4, default 3): 3
First sector (10487808-1953525167, default 10487808):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (10487808-1953525167, default 1953525167):
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Created a new partition 3 of type 'Linux' and of size 926.5 GiB.

After completing these steps, pressing p should display a partition table that looks similar to this:

Command (m for help):p
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: HGST HTS721010A9
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0xf163b576
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Device     Boot    Start        End    Sectors   Size Id Type
/dev/sda1  *        2048    2099199    2097152     1G 83 Linux
/dev/sda2        2099200   10487807    8388608     4G 82 Linux swap / Solaris
/dev/sda3       10487808 1953525167 1943037360 926.5G 83 Linux

Saving the partition layout

Press w to write the partition layout and exit fdisk:

Command (m for help):w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

Now it is time to put filesystems on the partitions.