Category Archives: How To

Firejail on Linux to sandbox all the things

Firejail is a program that can prepare sandboxes to run other programs. This is an efficient way to keep a software isolated from the rest of the system without need of changing its source code, it works for network, graphical or daemons programs.

You may want to sandbox programs you run in order to protect your system for any issue that could happen within the program (security breach, code mistake, unknown errors), like Steam once had a “rm -fr /” issue, using a sandbox that would have partially saved a part of the user directory. Web browsers are major tools nowadays and yet they have access to the whole system and have many security issues discovered and exploited in the wild, running it in a sandbox can reduce the data a hacker could exfiltrate from the computer. Of course, sandboxing comes with an usability tradeoff because if you only allow access to the ~/Downloads/ directory, you need to put files in this directory if you want to upload them, and you can only download files into this directory and then move them later where you really want to keep your files.


Securely Run Programs In Linux Mint Using Firetools

For running applications sandboxed in Linux, Firetools is a good utility to do so. Sandboxing is essentially restricting applications in their own space and thereby limiting their reach to the overall system. This is a security layer to prevent any malicious programs to have full access to the system.

Firetools is a graphical front-end for the command-line sandboxing tool Firejail.


Firejail Tips and Tricks


Mainly Tor and DNS because that’s what I’ve been doing lately.



Before we start, let’s get into the habit of cleaning up some files when we shut down the computer. For this you need a systemd unit file (see Appendix 1) and a simple script (see Apendix 2). Copy the unit file in /etc/systemd/system directory, and the script in /etc. The contents of the script is as follows:

rm -fr /home/netblue/.cache

.cache directory is the place where people find copies of all the webpages you visited, torrent trackers you connected to, and all that emails you thought you deleted – all 3 GB of them!

After that, take a look at /etc/machine-id. This is a world-readable file containing a huge random number:

$ cat /etc/machine-id

Sort of a serial number, it is used to uniquely identify Linux computers. You definitely don’t want it on your home network. But since it is required by systemd, generate a new one on shutdown. Actually, there is another copy of this file in /var/lib/dbus/machine-id, so you have to deal with both of them:

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Simple Application Sandboxing Using AppArmor and Firejail

Security is one of the most important and overlooked aspects of modern computing. We tend to let the default security configurations do the work, or on Windows, we simply install some anti-virus and be done with it. However, applications are increasingly privileged and we find ourselves running programs that could represent a security vulnerability to our systems and, more importantly, to our information.

Sandboxing allows us to limit what each application can see and what it can access, as well as what it can do in your system. Clearly not all applications need sandboxing, for example, your text editor probably isn’t a security vulnerability. Regardless, applications like browsers are the source of many security vulnerabilities, even though they already do some sandboxing themselves.

In this post, we will use a very simple sandboxing method using Firejail and AppArmor on Linux.


How to improve Signal Desktop’s usability under Firejail

If you use Firejail to run Signal Desktop in a sandboxed environment on Linux, you will likely be surprised by the fact that a new application instance is opened every time you execute the firejail signal-desktop command. Attempting to open a second instance of Signal Deskop should simply cause the existing one to be activated instead, but Firejail breaks this default behavior.

On top of that, if you use the –use-tray-icon parameter to have Signal Desktop place an icon on your desktop environment’s icon tray, the icon may not only be displayed incorrectly, but each new opened instance will place an additional (incorrect) icon there as well, making things even worse.

Addressing these issues is fortunately easy. All you need to do is create a Firejail profile file named signal-desktop.profile inside the ~/.config/firejail/ directory containing the following: