GPT fdisk

https://www.rodsbooks.com/gdisk/
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GPT fdisk is a set of text-mode partitioning tools for Linux, macOS, FreeBSD, and Windows that...
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### Create a new partition with sgdisk

Source: https://www.rodsbooks.com/gdisk/sgdisk.html

Example of creating a new partition on /dev/sdc using the -n option.

```bash
sgdisk -n 2:2000:50000 /dev/sdc
```

--------------------------------

### Start gdisk on a device

Source: https://www.rodsbooks.com/gdisk/walkthrough.html

Launch the gdisk utility on a specific device, such as /dev/sdf, to begin partition management.

```bash
# **gdisk /dev/sdf**
GPT fdisk (gdisk) version 1.0.9

Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: not present


***************************************************************
Found invalid GPT and valid MBR; converting MBR to GPT format
in memory. THIS OPERATION IS POTENTIALLY DESTRUCTIVE! Exit by
typing 'q' if you don't want to convert your MBR partitions
to GPT format!
***************************************************************


Command (? for help):
```

--------------------------------

### Example build failure output

Source: https://www.rodsbooks.com/gdisk/download.html

An example of error output indicating a missing development package, specifically popt.h.

```text
g++  -Wall -D_FILE_OFFSET_BITS=64   -c -o sgdisk.o sgdisk.cc
sgdisk.cc:13:18: error: popt.h: No such file or directory
sgdisk.cc: In function 'int main(int, char**)':
sgdisk.cc:58: error: 'poptContext' was not declared in this scope
```

--------------------------------

### cgdisk prompts for creating a new partition

Source: https://www.rodsbooks.com/gdisk/cgdisk-walkthrough.html

The four prompts cgdisk displays when creating a new partition: first sector, size in sectors or {KMGTP}, hex code or GUID for the partition type, and the partition name. The example shows entering 4G for size, 0700 for type (Microsoft basic data), and 'Shared data' for the name.

```text
First sector (2048-30719966, default = 2048):
Size in sectors or {KMGTP} (default = 30715904): **4G**
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): **0700**
Current partition name is ''
Enter new partition name, or  to use the current name:
**Shared data**

```

--------------------------------

### Configure GRUB Legacy chainloading

Source: https://www.rodsbooks.com/gdisk/hybrid.html

Example configuration for GRUB Legacy to chainload a captured MBR image from a specific partition.

```text
title OpenSolaris 2008.11 captured MBR
        root (hd0,1)
        chainloader (hd1,4)/hda-solaris-mbr.img
```

--------------------------------

### Launch gdisk and display partition table

Source: https://www.rodsbooks.com/gdisk/hybrid.html

Start the gdisk utility for a specific device and use the 'r' command to enter the recovery/transformation menu, followed by 'p' to list the current partitions.

```bash
# **gdisk /dev/sdc**
GPT fdisk (gdisk) version 1.0.9

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): **r**

recovery/transformation command (? for help): **p**
Disk /dev/sdc: 15654912 sectors, 7.5 GiB
Model: USB Flash Drive
Sector size (logical/physical): 512/512 bytes
Disk identifier (GUID): E1F3535B-8F5B-1579-E04A-D8DEF36B8302
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 15654878
Partitions will be aligned on 8-sector boundaries
Total free space is 6 sectors (3.0 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40         3072007   1.5 GiB     AF00  Apple HFS/HFS+
   2         3072008         7266311   2.0 GiB     8300  Linux filesystem
   3         7266312        15654878   4.0 GiB     0700  Microsoft basic data

recovery/transformation command (? for help):  
```

--------------------------------

### read_lba()

Source: https://www.rodsbooks.com/gdisk/efi.c

Reads a specified number of bytes from a block device starting at a given LBA.

```c
static size_t
read_lba(struct block_device *bdev, u64 lba, u8 * buffer, size_t count)
{
	size_t totalreadcount = 0;
	sector_t n = lba * (bdev_logical_block_size(bdev) / 512);

	if (!bdev || !buffer || lba > last_lba(bdev))
                return 0;

	while (count) {
		int copied = 512;
		Sector sect;
		unsigned char *data = read_dev_sector(bdev, n++, &sect);
		if (!data)
			break;
		if (copied > count)
			copied = count;
		memcpy(buffer, data, copied);
		put_dev_sector(sect);
		buffer += copied;
		totalreadcount +=copied;
		count -= copied;
	}
	return totalreadcount;
}
```

--------------------------------

### Create and Configure Partitions with gdisk

Source: https://www.rodsbooks.com/gdisk/walkthrough.html

This sequence shows creating two additional partitions, filtering for Linux and FreeBSD partition types, and assigning specific hex codes.

```text
Command (? for help): **n**
Partition number (2-128, default 2): 
First sector (34-30719966, default = 16779264) or {+-}size{KMGTP}: 
Last sector (16779264-30719966, default = 30717951) or {+-}size{KMGTP}: **+4G**
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): **L**
Type search string, or  to show all codes: **Linux**
8200 Linux swap                          8300 Linux filesystem
8301 Linux reserved                      8302 Linux /home
8303 Linux x86 root (/)                  8304 Linux x86-64 root (/)
8305 Linux ARM64 root (/)                8306 Linux /srv
8307 Linux ARM32 root (/)                8308 Linux dm-crypt
8309 Linux LUKS                          830a Linux IA-64 root (/)
830b Linux x86 root verity               830c Linux x86-64 root verity
830d Linux ARM32 root verity             830e Linux ARM64 root verity
830f Linux IA-64 root verity             8310 Linux /var
8311 Linux /var/tmp                      8312 Linux user's home
8313 Linux x86 /usr                      8314 Linux x86-64 /usr
8315 Linux ARM32 /usr                    8316 Linux ARM64 /usr
8317 Linux IA-64 /usr                    8318 Linux x86 /usr verity
8319 Linux x86-64 /usr verity            831a Linux ARM32 /usr verity
831b Linux ARM64 /usr verity             831c Linux IA-64 /usr verity
8500 Container Linux /usr                8501 Container Linux resizable rootfs
8502 Container Linux /OEM customization  8503 Container Linux root on RAID
8e00 Linux LVM                           fd00 Linux RAID
   
Hex code or GUID (L to show codes, Enter = 8300): **8300**
Changed type of partition to 'Linux filesystem'

Command (? for help): **n**
Partition number (3-128, default 3): 
First sector (34-30719966, default = 25167872) or {+-}size{KMGTP}: 
Last sector (25167872-30719966, default = 30717951) or {+-}size{KMGTP}:
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): **L**
Type search string, or  to show all codes: **FreeBSD**
a500 FreeBSD disklabel                   a501 FreeBSD boot
a502 FreeBSD swap                        a503 FreeBSD UFS
a504 FreeBSD ZFS                         a505 FreeBSD Vinum/RAID
a506 FreeBSD nandfs                      
Hex code or GUID (L to show codes, Enter = 8300): **a503**
Changed type of partition to 'FreeBSD UFS'
```

--------------------------------

### Create filesystems on Linux

Source: https://www.rodsbooks.com/gdisk/walkthrough.html

Commands to create a FAT32 filesystem and an ext4 filesystem on the specified partitions.

```bash
# mkdosfs /dev/sdf1
# mkfs -t ext4 /dev/sdf2
```

--------------------------------

### Create partitions with type codes using sgdisk -n and -t

Source: https://www.rodsbooks.com/gdisk/sgdisk-walkthrough.html

Creates two new partitions on /dev/sdf using default start points and sizes specified with +5G and +7G, then sets their type codes to 0700 (Microsoft basic data) and A503 (FreeBSD UFS). The -p option prints the resulting partition table, showing the new partitions and their attributes.

```bash
# **sudo sgdisk -n 2:0:+5G -n 3:0:+7G -t 2:0700 -t 3:a503 /dev/sdf -p**
Disk /dev/sdf: 30720000 sectors, 14.6 GiB
Model: STORE N GO      
Sector size (logical/physical): 512/512 bytes
Disk identifier (GUID): 739CB37E-1201-47C2-9304-036EE67223F0
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 30719966
Partitions will be aligned on 2048-sector boundaries
Total free space is 1359805 sectors (664.0 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048         4196351   2.0 GiB     8300  
   2         4196352        14682111   5.0 GiB     0700  
   3        14682112        29362175   7.0 GiB     A503  
The operation has completed successfully.

```

--------------------------------

### Change a partition name with sgdisk

Source: https://www.rodsbooks.com/gdisk/sgdisk.html

Example of changing the GPT name of partition 1 on /dev/sdb to 'Sample Name'.

```bash
sgdisk -c 1:"Sample Name" /dev/sdb
```

--------------------------------

### Verify GPT Data Structures Output

Source: https://www.rodsbooks.com/gdisk/cgdisk-walkthrough.html

Example output from the Verify command indicating no problems found and the availability of free sectors.

```text
No problems found. 4029 free sectors (2.0 MiB) available in 2
segments, the largest of which is 2015 (1007.5 KiB) in size.
```
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