So you can use -d to look at a directory, but you can also use -R to do the opposite -- not just look inside a directory, but recursively look inside all the directories inside that directory! We won't include any example output for this option (since it's generally voluminous), but you may want to try a few ls -R and ls -Rl commands to get a feel for how this works.

Finally, the -i ls option can be used to display the inode numbers of the filesystem objects in the listing:

$ ls -i /usr
   1409 X11R6        314258 i686-linux           43090 libexec        13394 sbin
   1417 bin            1513 i686-pc-linux-gnu     5120 local          13408 share
   8316 distfiles      1517 include                776 man            23779 src
     43 doc            1386 info                 93892 portage        36737 ssl
  70744 gentoo-x86     1585 lib                   5132 portage.old      784 tmp