Permissions

Here’s a single file from our ls -l file listing earlier:

-rwxr-xr-x   1 root root     13928 Jul  7  2020 libtiffxx.so.4.3.7

Specifically, look at the permission bits:

-rwxr-xr-x
 ^^^^^^^^^

They are displayed in three groups of three here. Imagine them separated into three groups, to make it easier:

rwx r-x r-x

Each of these triplets represents read (r), write (w), and execute (x) permissions for a specific set of users, based on the user and group ownership information for that file. If you see a - character in place of a letter, that action (for the set of users it applies to) is not permitted.

1. The first three bits represent the permissions of the file owner. In this case, the file’s owner (root) can read, write, and execute the file – rwx.
2. The second three bits represent permissions for the group owner of the file, which in this case is also root. The permissions here are r-x, or read and execute (no writing!). But because root is also the user...