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 and the file system supports on-line resizing. (Modern Linux 2.6 kernels will support on-line resize for file systems mounted using ext3 and ext4; ext3 file systems will require the use of file systems with the resize_inode feature enabled.)
The size parameter specifies the requested new size of the filesystem. If no units are specified, the units of the size parameter shall be the filesystem blocksize of the filesystem. Optionally, the size parameter may be suffixed by one of the following the units designators: 's', 'K', 'M', or 'G', for 512 byte sectors, kilobytes, megabytes, or gigabytes, respectively. The size of the filesystem may never be larger than the size of the partition. If size parameter is not specified, it will default to the size of the partition.
Note: when kilobytes is used above, I mean real, power-of-2 kilobytes, (i.e., 1024 bytes), which some politically correct folks insist should be the stupid-sounding ``kibibytes''. The same holds true for megabytes, also sometimes known as ``mebibytes'', or gigabytes, as the amazingly silly ``gibibytes''. Makes you want to gibber, doesn't it?
The resize2fs program does not manipulate the size of partitions. If you wish to enlarge a filesystem, you must make sure you can expand the size of the underlying partition first. This can be done using fdisk(8) by deleting the partition and recreating it with a larger size or using lvextend(8), if you're using the logical volume manager lvm(8). When recreating the partition, make sure you create it with the same starting disk cylinder as before! Otherwise, the resize operation will certainly not work, and you may lose your entire filesystem. After running fdisk(8), run resize2fs to resize the ext2 filesystem to use all of the space in the newly enlarged partition.
If you wish to shrink an ext2 partition, first use resize2fs to shrink the size of filesystem. Then you may use fdisk(8) to shrink the size of the partition. When shrinking the size of the partition, make sure you do not make it smaller than the new size of the ext2 filesystem!
The -b and -s options enable and disable the 64bit feature, respectively. The resize2fs program will, of course, take care of resizing the block group descriptors and moving other data blocks out of the way, as needed. It is not possible to resize the filesystem concurrent with changing the 64bit status.