root@metis:/tmp# fdisk /dev/mmcblk1

Welcome to fdisk (util-linux 2.37.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/mmcblk1: 1.87 GiB, 2002780160 bytes, 3911680 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device         Boot Start     End Sectors  Size Id Type
/dev/mmcblk1p1       2048 3911679 3909632  1.9G  c W95 FAT32 (LBA)

* 出荷時の FAT32 Partition 削除 (Optional)

Command (m for help): d
Selected partition 1
Partition 1 has been deleted.

* No.1 Partition 作成 (FAT32, 256MB)

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 (2048-3911679, default 2048): 
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-3911679, default 3911679): +256M

Created a new partition 1 of type 'Linux' and of size 256 MiB.

Command (m for help): t
Selected partition 1
Hex code or alias (type L to list all): c
Changed type of partition 'Linux' to 'W95 FAT32 (LBA)'.

* No.2 Partition 作成 (Linux, 残り全部)

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 (526336-3911679, default 526336): 
Last sector, +/-sectors or +/-size{K,M,G,T,P} (526336-3911679, default 3911679): 

Created a new partition 2 of type 'Linux' and of size 1.6 GiB.

* 確認、書込して終了

Command (m for help): p
Disk /dev/mmcblk1: 1.87 GiB, 2002780160 bytes, 3911680 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device         Boot  Start     End Sectors  Size Id Type
/dev/mmcblk1p1        2048  526335  524288  256M  c W95 FAT32 (LBA)
/dev/mmcblk1p2      526336 3911679 3385344  1.6G 83 Linux

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

root@metis:/tmp# mkfs.vfat /dev/mmcblk1p1 
mkfs.fat 4.2 (2021-01-31)

root@metis:/tmp# mkfs.ext4 -m 0 /dev/mmcblk1p2 
mke2fs 1.46.5 (30-Dec-2021)
Discarding device blocks: done                            
Creating filesystem with 423168 4k blocks and 105872 inodes
Filesystem UUID: a20ecf5a-b0ce-4d1f-8464-283bd34fc3e4
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376, 294912

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done 

root@metis:/tmp# mount /dev/mmcblk1p1 /mnt/sd/
root@metis:/tmp# cd /mnt/sd/
root@metis:/mnt/sd# tar axf /tmp/sd_p1.tar.zst 
root@metis:/mnt/sd# sync
root@metis:/mnt/sd# cd ..
root@metis:/mnt# umount /mnt/sd 

root@metis:/mnt# mount /dev/mmcblk1p2 /mnt/sd/
root@metis:/mnt# cd sd/

ここに 開発用 - Ubuntu 22.04LTS(Jammy Jellyfish) ベース に置いてある、root filesystem のアーカイブ(tar.xz ファイル)を展開