resize2fs - The resize2fs program will resize ext2 or ext3 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
ext2online - he ext2online tool resizes ext2 file systems while they are mounted and in use by the system. It is OK to resize the filesystem even while programs have open files and are writing into the filesystem. It is only possible to enlarge a mounted filesystem. To be able to use ext2online, you need to have the Online ext2 resize support (CONFIG_EXT2_RESIZE) feature enabled in the kernel
Tresize2fs - he resize2fs program does not manipulate the size of partitions. If you wish to enlarge a filesystem, you must first make sure you can expand the size of the underlying partition first.
ext2online - The ext2online program does not change the size of the actual device - only the filesystem. If you wish to enlarge a filesystem, you must make sure you expand the underlying device first.
You can shrink partitions using resize2fs but u cant do it with ext2onilne.
FYI - The ext2online tool can currently only resize ext3 filesystems online, despite references to ext2 filesystems in this manpage. The ext2resize tool can resize either ext2 or ext3 filesystems, offline.
ref : -
http://linux.die.net/man/8/resize2fshttp://linux.die.net/man/8/ext2onlinehope this helps
