# mkfs -t ext4 /tmp/image1

will create a ext2 filesystem on image1, if its not big enough (warning “Filesystem too small for a journal” means a filesystem without a journal, a.k.a. ext2, is created)

If you don’t realize this and nevertheless mount it as ext4. The df and mount methods above will mirror back ext4:

$ df -Th /tmp/mnt*
Filesystem     Type  Size  Used Avail Use% Mounted on
/dev/loop4     ext4 1003K   24K  908K   3% /tmp/mnt1
/dev/loop5     ext4  987K   33K  812K   4% /tmp/mnt2
$ mount | grep mnt
...
/home/mallikab/image1 on /tmp/mnt1 type ext4 (rw,relatime,seclabel)
/home/mallikab/image2 on /tmp/mnt2 type ext4 (rw,relatime,seclabel,data=ordered)

but fsck and file reveal the true filesystem:

$ fsck -N /tmp/mnt1
fsck from util-linux 2.23.2
[/sbin/fsck.ext2 (1) -- /tmp/mnt1] fsck.ext2 /tmp/mnt1 
$ fsck -N /tmp/mnt2
fsck from util-linux 2.23.2
[/sbin/fsck.ext4 (1) -- /tmp/mnt2] fsck.ext4 /home/mallikab/image2 

$ file -sL /home/mallikab/image2 
/home/mallikab/image2: Linux rev 1.0 ext4 filesystem data, UUID=b4e8e086-54ca-4d9d-9f38-32bbed211e6b (needs journal recovery) (extents) (64bit) (huge files)
$ file -sL /home/mallikab/image1
/home/mallikab/image1: Linux rev 1.0 ext2 filesystem data (mounted or unclean), UUID=09b3a8c9-0b6d-43c5-b195-c45f6c091765 (extents) (64bit) (huge files)

hm, although fsck doesn't indicate ext2 unless the images are mounted, i.e.
$ fsck -N ~/image1
fsck from util-linux 2.23.2
[/sbin/fsck.ext4 (1) -- /home/mallikab/image1] fsck.ext4 /home/mallikab/image1

@Zac

Thanks for the useful feedback.

@mic

We very much appreciate you too. Many thanks for the feedback.

but I appreciate very much this page :)