permissions – Sick Gaming

We all have people around us, whom we hold dear. Some of them might even rely on you to keep them save. And since the world is constantly changing, that can be a challenge. No more is this apparent than with children, and Linux has long been lacking simple tools to help parents. But that is changing, and here we’ll talk about the new parental controls that Fedora Linux provides.

Users and permissions

First, it’s important to know that any Linux system has a lot of options for user, group, and permission management. Many of these advanced tools are aimed at professional users, though, and we won’t be talking about those here. In this article we’ll focus on home users.

Additionally, parental controls are not just useful for parents. You can use them when helping family members who are technically illiterate. Or perhaps you want to configure a basic workstation for simple administrative tasks. Either way, parental control can offer many security and reliability benefits.

Creating users

From the Settings panel, you can navigate to Users and from there you can select Add User… (after unlocking) to add a new user. You can give them a personal name, a username and their own icon. You can even decide if somebody else should also be an administrator.

Adding a user to your machine is as simple as going to settings, users, and clicking Add User…

You can also set a default password, or even allow a computer to automatically log in. You should help others understand digital security and the value of passwords, but for some people it might be better to just auto-login.

Admin rights

When you give somebody administrator rights, that user will have the same powers as you have on the system. They will be able to make any system change they prefer, and they can also add and remove users themselves.

Users who do not have admin rights, will not be able to make fundamental changes to the computer. They can still use all applications that are already on the system, and they can even download applications from the internet to their home folder. Still, they are ultimately blocked from doing anything that could damage the system.

Accessing the user-directories of others. Only administrator users will be able to do this.

Don’t forget that as an administrator, you can always reset a password. You can also enter another user’s home directory in case you have to. As with all ‘sudo’ rights, you should be careful and you should be considerate of other’s privacy.

Application control

Once one or multiple users are created, you can choose to tweak and control what applications somebody can use. This is done from within Settings > Users by selecting the new user then selecting Parental Controls and then Restrict Applications. Other options are available there, as well.

changing Parental Controls for a single user.

However, there is a big caveat

Parental controls come with a big caveat: If you want a simple home-user solution, you MUST use Flatpaks.

The problem is as follows. The existing Linux application landscape is quite complex, and it would be almost impossible to introduce a new user-friendly application-control system this late into its life cycle. Thus, the second best solution is to ensure that the next generation of packaging has such functionality from the start.

To use Flatpaks, you can use the Fedora’s repository, or the Flathub repository. If you want to know all the fine details about those projects, then don’t forget to read this recent comparison.

Compromise and limitations

No article would be complete without mentioning the inherit limitations of the parental controls. Besides all the obvious limits of computers not knowing right from wrong, there are also some technical limits to parental controls.

Parental Control’s limits

The security that Parental Controls provides will only work as long as Fedora Linux is running in working order. One could easily bypass all controls by flashing Fedora on a USB stick and starting from a clean, root-powered, installation image. At this point, human supervision is still superior to the machine’s rules.

Adding to that, there are the obvious issues of browsers, store fronts like Steam, and other on-line applications. You can’t block just parts of these applications. Minecraft is a great game for children, but it also allows direct communication with other people. Thus, you’ll have to constantly juggle permissions. Here too, it is better to focus on the human element instead of relying to much on the tools.

Finally, don’t forget about protecting the privacy and well-being of others online. Blocking bad actors with Ublock Origin and/or a DNS based blocker will also help a lot.

Legacy applications

As mentioned before, Fedora and Parental Controls only work with Flatpaks. Every application that is already on the system can be started by users who otherwise don’t have the permissions.

As a rule of thumb; If you want to share a computer with vulnerable family members, don’t install any software that’s inappropriate using the RPM Repositories. Instead, consider using a Flatpak.

Starting the system-wide installation of Firefox from the Terminal. The Flatpak version of Firefox though, will not start.

Summary

There is much that you can do to help those who are less experienced with computers. By simply giving these users their own account and using Flatpaks, you can make their lives a lot easier. Age restrictions can even offer additional benefits. But it’s not all perfect, and good communication and supervision will still be important.

The Parental Controls will improve over time. They have been given more priority in the past few years and there are additional plans. Time-tracking is, for example planned. As the migration to Flatpaks continues, you can expect that more software will respect age-restrictions in the future.

Additional US and UK resources

Sharing Fedora Linux with Parental Controls

So, let’s start a small collaboration here. We’ve all been younger, so how did you escape your parents’ scrutiny? And for those who are taking care of others… how are you helping others? Let’s see what we can learn from each other.

A previous article covered some basics about file permissions on your Fedora system. This installment shows you additional ways to use permissions to manage file access and sharing. It also builds on the knowledge and examples in the previous article, so if you haven’t read that one, do check it out.

Symbolic and octal

In the previous article you saw how there are three distinct permission sets for a file. The user that owns the file has a set, members of the group that owns the file has a set, and then a final set is for everyone else. These permissions are expressed on screen in a long listing (ls -l) using symbolic mode.

Each set has r, w, and x entries for whether a particular user (owner, group member, or other) can read, write, or execute that file. But there’s another way to express these permissions: in octal mode.

You’re used to the decimal numbering system, which has ten distinct values (0 through 9). The octal system, on the other hand, has eight distinct values (0 through 7). In the case of permissions, octal is used as a shorthand to show the value of the r, w, and x fields. Think of each field as having a value:

r = 4
w = 2
x = 1

Now you can express any combination with a single octal value. For instance, read and write permission, but no execute permission, would have a value of 6. Read and execute permission only would have a value of 5. A file’s rwxr-xr-x symbolic permission has an octal value of 755.

You can use octal values to set file permissions with the chmod command similarly to symbolic values. The following two commands set the same permissions on a file:

chmod u=rw,g=r,o=r myfile1
chmod 644 myfile1

Special permission bits

There are several special permission bits also available on a file. These are called setuid (or suid), setgid (or sgid), and the sticky bit (or delete inhibit). Think of this as yet another set of octal values:

setuid = 4
setgid = 2
sticky = 1

The setuid bit is ignored unless the file is executable. If that’s the case, the file (presumably an app or a script) runs as if it were launched by the user who owns the file. A good example of setuid is the /bin/passwd utility, which allows a user to set or change passwords. This utility must be able to write to files no user should be allowed to change. Therefore it is carefully written, owned by the root user, and has a setuid bit so it can alter the password related files.

The setgid bit works similarly for executable files. The file will run with the permissions of the group that owns it. However, setgid also has an additional use for directories. If a file is created in a directory with setgid permission, the group owner for the file will be set to the group owner of the directory.

Finally, the sticky bit, while ignored for files, is useful for directories. The sticky bit set on a directory will prevent a user from deleting files in that directory owned by other users.

The way to set these bits with chmod in octal mode is to add a value prefix, such as 4755 to add setuid to an executable file. In symbolic mode, the u and g can be used to set or remove setuid and setgid, such as u+s,g+s. The sticky bit is set using o+t. (Other combinations, like o+s or u+t, are meaningless and ignored.)

Sharing and special permissions

Recall the example from the previous article concerning a finance team that needs to share files. As you can imagine, the special permission bits help to solve their problem even more effectively. The original solution simply made a directory the whole group could write to:

drwxrwx---. 2 root finance 4096 Jul 6 15:35 finance

One problem with this directory is that users dwayne and jill, who are both members of the finance group, can delete each other’s files. That’s not optimal for a shared space. It might be useful in some situations, but probably not when dealing with financial records!

Another problem is that files in this directory may not be truly shared, because they will be owned by the default groups of dwayne and jill — most likely the user private groups also named dwayne and jill.

A better way to solve this is to set both setgid and the sticky bit on the folder. This will do two things — cause files created in the folder to be owned by the finance group automatically, and prevent dwayne and jill from deleting each other’s files. Either of these commands will work:

sudo chmod 3770 finance
sudo chmod u+rwx,g+rwxs,o+t finance

The long listing for the file now shows the new special permissions applied. The sticky bit appears as T and not t because the folder is not searchable for users outside the finance group.

drwxrws--T. 2 root finance 4096 Jul 6 15:35 finance