далеко ходить не будем, здесь ext3 или ext4
Не будем. Дойдём до man-страницы:
RESIZE2FS(8) RESIZE2FS(8)
NAME
resize2fs - ext2/ext3/ext4 file system resizer
SYNOPSIS
resize2fs [ -fFpPM ] [ -d debug-flags ] [ -S RAID-stride ] device [ size ]
DESCRIPTION
The resize2fs program will resize ext2, ext3, or ext4 file systems. It can be used to enlarge or shrink an unmounted file system
located on device. If the filesystem is mounted, it can be used to expand the size of the mounted filesystem, assuming the kernel
supports on-line resizing.
...
В данном случае как раз и нужно уменьшить размер файловой системы.