Options which I find most useful, and use often.
 -a : lists all files in the given directory, including those whose names start with “.” (which are hidden files in Unix). By default, these files are excluded from the list.
 -R : recursively lists subdirectories. The command ls -R / would therefore list all files
 -h : print sizes in human readable format. (e.g., 1K, 234M, 2G, etc.) This option is not part of the POSIX standard, although implemented in several systems, e.g., GNU coreutils in 1997, FreeBSD 4.5 in 2002, and Solaris 9 in 2002.