The ext4 filesystem is known as the forth extended filesystem, and is the default file system on many Linux distributions.
To Format a partition with the ext4 filesystem run the following command:
$ sudo mkfs.ext4 /dev/sdc1
Replace sdc1 with the relevent disk and partition that you want to format. In this example, the disk is /dev/sdc, and its the first partition on that disk. Make sure you get the drive and partition correct or you may wipe something that you dont want to.
Example:
$ sudo mkfs.ext4 /dev/sdc1
mke2fs 1.43.4 (31-Jan-2017)
Creating filesystem with 261888 4k blocks and 65536 inodes
Filesystem UUID: 15d8146f-bcb3-414c-864f-5100bb4b0bf8
Superblock backups stored on blocks:
32768, 98304, 163840, 229376
Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
$
If the parition already has a filesystem on it, you should get a warning such as this:
$ sudo mkfs.ext4 /dev/sdc1
mke2fs 1.43.4 (31-Jan-2017)
/dev/sdc1 contains a ext4 file system
created on Sun Jun 4 22:59:38 2017
Proceed anyway? (y,N)
Press “y” and enter to confirm you want to overwrite the file system.