Which type of filesystem is created by mkfs when it is executed with the block device name only and without any additional parameters?

mkfs is a front-end that calls filesystem-specific creation tools. When no -t type argument is provided, the default filesystem type compiled into mkfs is ext2. This behavior is defined by the mkfs implementation on Linux systems, where ext2 is the historical default, and no journaling or extended features are added unless a type like ext3 or ext4 is explicitly requested.

ext3 includes a journal layer on top of ext2 and must be explicitly requested with mkfs -t ext3 or mkfs.ext3.

ext4 is a more modern journaling filesystem that must be explicitly specified with mkfs -t ext4 or mkfs.ext4.

XFS is a completely different filesystem that must be explicitly specified using mkfs -t xfs or mkfs.xfs.

VFAT is a FAT-based filesystem used for compatibility with Windows and must be explicitly specified using mkfs -t vfat or mkfs.vfat.