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gdisk Tutorial

Tutorial using gdisk on jailbroken iOS/tvOS/bridgeOS.

Notes

This tutorial is for people that do not have experience with command-line partitioning with gdisk on Linux/Unix. If you know already, you may skip reading. Keep in mind that the sector size is 4096.

Common Partition codes

These partition codes may be used later.

0700 = Microsoft basic data
8200 = Linux swap
8300 = Linux filesystem
AF00 = Apple HFS/HFS+
AF0A = Apple APFS

Partitioning

You should have ran resize_apfs to resize the apfs filesystem already. After resizing the filesystem, the partition table needs to be updated.

Start by running gdisk against the main disk.

# ./gdisk /dev/disk0

You should get:

GPT fdisk (gdisk) version 1.0.10

Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Type p and enter to print the current partition table:

Command (? for help): p
Disk /dev/disk0: 62500000 sectors, 238.4 GiB
Sector size (logical): 4096 bytes
Disk identifier (GUID): 37FE5887-699F-463D-A34F-98CA0D99FBA3
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 5
First usable sector is 6, last usable sector is 62499994
Partitions will be aligned on 2-sector boundaries
Total free space is 1 sectors (4.0 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1               6        62499993   238.4 GiB   AF0A  Apple APFS

Then we will actually delete this partition since there's no such thing as resizing partition in gdisk. The changes are not written out until a w command is issued.

Type d and enter to delete a partition. Since there is only one partition, the partition will be automatically selected and deelted.

Command (? for help): d
Using 1

Then we need to create a new partition that exactly matches the size of the resized filesystem. Start and end are inclusive and each sector is 4096 bytes long.

Type n, enter, and 1, enter. For start, keep it at 6 like it originally is. For end, suppose the filesystem is resized to be 192000000000 bytes (this size must be sector-aligned), then the last sector is (6 + (192000000000) / 4096) - 1 = 46875005 In general for a 4096-byte aligned filesystem size n, the last sector is (start + (size) / 4096) - 1.

Type start and end sector. As for type code, use AF0A for Apple APFS:

Command (? for help): n
Partition number (1-128, default 1): 1
First sector (6-62499994, default = 6) or {+-}size{KMGTP}: 6
Last sector (6-62499994, default = 62499993) or {+-}size{KMGTP}: 46875005
Current type is AF00 (Apple HFS/HFS+)
Hex code or GUID (L to show codes, Enter = AF00): AF0A
Changed type of partition to 'Apple APFS'

Now the APFS partition is restored. Custom partitions can now be created, suppose we want a partition to hold the rootfs:

Command (? for help): n
Partition number (2-128, default 2): 2
First sector (46875006-62499994, default = 46875006) or {+-}size{KMGTP}: 46875006
Last sector (46875006-62499994, default = 62499993) or {+-}size{KMGTP}: 61035156
Current type is AF00 (Apple HFS/HFS+)
Hex code or GUID (L to show codes, Enter = AF00): 8300
Changed type of partition to 'Linux filesystem'

where 8300 = Linux filesystem

And a partition to hold the boot files:

Command (? for help): n
Partition number (3-128, default 3): 3
First sector (61035157-62499994, default = 61035158) or {+-}size{KMGTP}: 61035264
Last sector (61035264-62499994, default = 62499993) or {+-}size{KMGTP}: 61157119
Current type is AF00 (Apple HFS/HFS+)
Hex code or GUID (L to show codes, Enter = AF00): 8300
Changed type of partition to 'Linux filesystem'

where 8300 = Linux filesystem

A FAT32 partition to hold earlier boot files:

Command (? for help): n
Partition number (4-128, default 4): 4
First sector (61035157-62499994, default = 61157120) or {+-}size{KMGTP}: 61157120
Last sector (61157120-62499994, default = 62499993) or {+-}size{KMGTP}: 61222655
Current type is AF00 (Apple HFS/HFS+)
Hex code or GUID (L to show codes, Enter = af00): 0700
Changed type of partition to 'Microsoft basic data'

where 0700 = Microsoft basic data

A swap partition:

Command (? for help): n
Partition number (5-128, default 5): 5
First sector (61035157-62499994, default = 61222656) or {+-}size{KMGTP}: 61222656
Last sector (61222656-62499994, default = 62499993) or {+-}size{KMGTP}: 62499839
Current type is af00 (Apple HFS/HFS+)
Hex code or GUID (L to show codes, Enter = af00): 8200
Changed type of partition to 'Linux swap'

In this example, 4 new partitions are created and the existing APFS partition is shrunk. Type p to print the new partition table and CHECK CAREFULLY to avoid data loss:

Command (? for help): p
Disk /dev/disk0: 62500000 sectors, 238.4 GiB
Sector size (logical): 4096 bytes
Disk identifier (GUID): 37FE5887-699F-463D-A34F-98CA0D99FBA3
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 5
First usable sector is 6, last usable sector is 62499994
Partitions will be aligned on 2-sector boundaries
Total free space is 262 sectors (1.0 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1               6        46875005   178.8 GiB   AF0A  Apple APFS
   2        46875006        61035156   54.0 GiB    8300  Linux filesystem
   3        61035264        61157119   476.0 MiB   8300  Linux filesystem
   4        61157120        61222655   256.0 MiB   0700  Microsoft basic data
   5        61222656        62499839   4.9 GiB     8200  Linux swap

When everything is good, type w, enter, confirm with y to actually write the partition table:

Command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT) to /dev/disk0.
Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Warning: The kernel may continue to use old or deleted partitions.
You should reboot or remove the drive.
The operation has completed successfully.

Now, check /dev to ensure the partitions /dev/disk0s2, /dev/disk0s3, ... are created.

Now the partitions has been created. However, there are no filesystem on them. You will need to flash prebuilt filesystem images with dd, and for some other partitions, format them once booted into Linux. The filesystem images likely has to have a block size of 4096.

For example, to flash a filesystem image, root.img into the second partition:

# dd if=root.img of=/dev/disk0s2

For Apple A11, the partition will show up as /dev/nvme0n1p... in Linux. For example /dev/disk0s2 is /dev/nvme0n1p2 in Linux.