Lab Objective:
Learn how to manipulate file permissions and ownership settings.
Lab Purpose:
In this lab, you will learn to use chmod and chown, as well as view permissions and ownership settings with ls.
Lab Tool:
Ubuntu 18.04 (or another distro of your choice).
Lab Topology:
A single Linux machine, or virtual machine
Lab Walkthrough:
Task 1:
Open the Terminal and run:
- echo “Hello World” > foo
- ls -l foo
Look at the first field; you should see -rw-r–r–
This indicates the user, group, and other permissions. The last nine characters, in groups of three, denote these permissions. In this instance:
rw- indicates read/write (but not execute) permissions for the user who owns the file
r– indicates read-only permissions for the group that owns the file
r– indicates read-only permissions for all non-owners, a.k.a. “world”
The first character indicates the type of file. In this case it is a regular file; directories begin with d.
Who are the user and group owners of this file? The third and fourth fields of ls -l tell us that. By default, it should be your own user and primary group.
Task 2:
Now run:
- sudo chown root foo
- ls -l foo
- cat foo
You’ve just changed the user ownership to root, while keeping the group ownership. As the file has group- and world-read permissions, you can still see its contents.
Task 3:
Now run:
- sudo chmod o-r foo
- ls -l foo
- cat foo
That chmod command removes read permissions from other. However, as you still have group ownership, you can still see the file’s contents.
Task 4:
Now run:
- sudo chmod 600 foo
- ls -l foo
- cat foo
This chmod command explicitly sets permissions to read-write for the owning user only. As that is the root, we can no longer read the file.
Task 5:
Finally, clean up with sudo rm foo
Notes:
Execute permissions apply to executable files as well as directories. If a user/group cannot “execute” a directory, it cannot view the contents of said directory or any subdirectories.
