-j     Add an ext3 journal to the filesystem.  If the -J option is not specified, the default journal parameters will be used to
              create an appropriately sized journal (given the size of the filesystem) stored within the  filesystem.   Note  that  you
              must be using a kernel which has ext3 support in order to actually make use of the journal.

              If  this  option is used to create a journal on a mounted filesystem, an immutable file, .journal, will be created in the
              top-level directory of the filesystem, as it is the only safe way to create the journal inode  while  the  filesystem  is
              mounted.   While  the ext3 journal is visible, it is not safe to delete it, or modify it while the filesystem is mounted;
              for this reason the file is marked immutable.  While checking unmounted filesystems, e2fsck(8)  will  automatically  move
              .journal  files  to  the  invisible,  reserved  journal inode.  For all filesystems except for the root filesystem,  this
              should happen automatically and naturally during the next reboot cycle.  Since the root filesystem is mounted  read-only,
              e2fsck(8) must be run from a rescue floppy in order to effect this transition.