Practical UNIX and Internet Security, 3rd Edition

File Attributes and Permissions

Now that we have a basic understanding of how filesystems work, we’ll turn our attention to understanding how filesystems influence the security of a Unix system. Nearly all of this discussion will be concerned with the metadata that a filesystem contains—the filenames, permissions, timestamps, and access control attributes.

Exploring with the ls Command

You can use the ls command to list all of the files in a directory. For instance, to list all the files in your current directory, type:

% ls
instructions  invoice       letter       more-stuff   notes      stats
%

Actually, ls alone won’t list all of the files. Files and directories beginning with a dot (“.”) are hidden from the ls command but are shown if you use ls -a:

% ls -a
.  ..  .indent  instructions  invoice  letter  notes  more-stuff  stats
%

The entries for “.” and “..” refer to the current directory and its parent directory, respectively. The file .indent is a hidden file. If you use ls -A instead of ls -a, you’ll see hidden files, but “.” and “..” will not be shown.

You can get a more detailed listing by using the ls -lF command:

% ls -lF
total 161
-rw-r--r-- 1 sian    user          505 Feb  9 13:19 instructions
-rw-r--r-- 1 sian    user         3159 Feb  9 13:14 invoice
-rw-r--r-- 1 sian    user         6318 Feb  9 13:14 letter
-rw------- 1 sian    user        15897 Feb  9 13:20 more-stuff
-rw-r----- 1 sian    biochem      4320 Feb  9 13:20 notes
-rwxr-xr-x 1 sian    user       122880 Feb  9 13:26 stats*
%

The first line of output generated by the ls command (total 161 in the example ...