These options change the order in which
ls sorts the information
it outputs. By default, sorting is done by character code
(e.g., ASCII order).
If the long listing format (e.g., -l, -o) is being used, print the status change time (the ‘ctime’ in the inode) instead of the modification time. When explicitly sorting by time (--sort=time or -t) or when not using a long listing format, sort according to the status change time.
Primarily, like -U—do not sort; list the files in whatever order they are stored in the directory. But also enable -a (list all files) and disable -l, --color, and -s (if they were specified before the -f).
Reverse whatever the sorting method is—e.g., list files in reverse alphabetical order, youngest first, smallest first, or whatever.
Sort by file size, largest first.
Sort by modification time (the ‘mtime’ in the inode), newest first.
If the long listing format (e.g., --format=long) is being used, print the last access time (the ‘atime’ in the inode). When explicitly sorting by time (--sort=time or -t) or when not using a long listing format, sort according to the access time.
Do not sort; list the files in whatever order they are stored in the directory. (Do not do any of the other unrelated things that -f does.) This is especially useful when listing very large directories, since not doing any sorting can be noticeably faster.
Sort by version name and number, lowest first. It behaves like a default sort, except that each sequence of decimal digits is treated numerically as an index/version number. (See Details about version sort.)
Sort directory contents alphabetically by file extension (characters after the last ‘.’); files with no extension are sorted first.