File and Folder Permissions on Raspberry Pi

In this post, we are going to see how the file and folder permission system works in a Linux-based operating system like Raspbian on Raspberry Pi.

We already have many posts within the Raspberry Pi section aimed at learning the fundamental handling of the Linux operating system, which will allow us to tackle more advanced tutorials.

Getting used to the file and folder permission system is another one of those things we will have to deal with sooner or later in Linux, as it is one of the main features of this operating system.

As we know, one of Linux’s strengths is its security. An important part of it relies on its simple but robust permission system. So it’s important to understand and handle them fluently.

Show Permissions in Linux

Each file and folder in Linux has an owner, an owner group, and a series of permissions associated with each of these roles. We can check the permissions simply by listing the files with this command

For example, the file ‘hola.txt’ we see has:

This means that the file owner is the user ‘pi’, and the user group is ‘pi’

On the other hand, the beginning of the line represents the permissions that the different user roles have over the file or folder.

Furthermore, the characters for each role represent a permission, being,

• r: read
• w: write
• x: execute

Change Owner

To change the owner user of a file or folder we use the ‘chown’ command (change owner)

We can change the permissions of all folders and subfolders of a directory recursively with the ‘-R’ parameter

We can also change the owner group of a file with the ‘chgrp’ command (change group)

Finally, we can change the user and group simultaneously with the following command.

Change Permissions

To change the permissions of a file we use the ‘chmod’ command. This command receives the different parameters

Thus, for example, to give full permissions to all roles we would use

If we want to apply the permissions to all files in a directory and subdirectory, we use the ‘-R’ parameter.

For example, if we wanted to remove write and execute permissions from other users recursively, we would do,

Octal Representation of Permissions

Finally, it is also very common to work with the octal representation of permissions. This shows the same information but grouped into 4 octal digits, where each octal groups the 3 permissions (r,w,x) of each user role.

• First octal, special permissions
• Second octal, owner user permissions
• Third octal, owner group permissions
• Fourth octal, other users permissions

The equivalence between the octal and the r-w-x equivalent is as follows.

With the octal representation, the ‘chmod’ command directly receives the desired permission, instead of adding them with ’+’ or ’-’.

For example, to give full permissions to the owner, and no permissions to the other roles we would do

For example, if we want to give full permissions to the owner user, read permission to the owner group, and none to the rest of the users, we would do

That’s all for the topic of permission management. At first it may seem cumbersome, but it’s actually a very robust and simple system.

With a little practice, you’ll get the hang of it quickly. See you in the next post! See you soon!