The tune2fs program can add a journal to an existing ext2 file system without altering the data already on the partition thus converting an ext2 file system to an ext3 file system.
To convert an ext2 file system to ext3, log in as root and type:
where is an appropriate file system such as /dev/hda6
After doing this, change the partition type from ext2 to ext3 in the /etc/fstab file for that partition.
Note: If you are converting your root file system, you must use an initrd image (or RAM disk) to boot. To create this, run the mkinitrd program. For information on using the mkinitrd command, type man mkinitrd. Also, make sure your GRUB configuration loads the initrd. If you fail to make this change, the system still boots, but the file system is mounted as ext2 instead of ext3.