### Change to EXT4 mount mode (OKAY before conversion)
vi /etc/fstab

### Reboot into single user mode
shutdown -r now
LILO: linux S

### Unmount or read-only every filesystem
umount -a
mount -oremount,ro /usr
mount -oremount,ro /

### Convert all ext4 into new metadata formats
grep ext4 /etc/fstab | tr -s [:space:] | cut -f 1 -d \ | tune2fs -O extents,uninit_bg,dir_index

### Build the directory index and verify metadata
grep ext4 /etc/fstab | tr -s [:space:] | cut -f 1 -d \ | fsck.ext4 -yfD

### Reboot back to multiuser mode
shutdown -r now

### Covert all files in EXT4 filesystems to extent mode (was bitmap)
for dir in `mount | grep ext4 | cut -f 3 -d \ ` ; do LC_ALL=C find $dir -xdev -type d -print0 | LC_ALL=C xargs -r0 -P3 chattr +e ; done
for dir in `mount | grep ext4 | cut -f 3 -d \ ` ; do LC_ALL=C find $dir -xdev -type f -print0 | LC_ALL=C xargs -r0 -P3 chattr +e ; done

### References
* https://debian-administration.org/article/643/Migrating_a_live_system_from_ext3_to _ext4_filesystem
* http://unix.stackexchange.com/questions/131535/recursive-grep-vs-find-type-f-exec-grep-which-is-more-efficient-faster