Firejail

Resources

Firejail is a SUID sandboxing program. It reduces the risk of security breaches by restricting the running environment of untrusted applications using, among other things, Linux namespaces and seccomp-bpf. The software includes security profiles for a large number of applications like Mozilla Firefox, Chromium, VLC, or Transmission.

Installation

USE flags

USE flags for sys-apps/firejail Security sandbox for any type of processes

`+chroot`	Enable chrooting to custom directory
`+dbusproxy`	Enable DBus proxying to filter access in supporting profiles
`+file-transfer`	Enable file transfers between sandboxes and the host system
`+globalcfg`	Enable global config file
`+network`	Enable networking features
`+private-home`	Enable private home feature
`+userns`	Enable attaching a new user namespace to a sandbox (--noroot option)
`X`	Enable X11 sandboxing
`apparmor`	Enable support for custom AppArmor profiles
`contrib`	Install contrib scripts
`selinux`	!!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur
`test`	Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)

Data provided by the Gentoo Package Database · Last update: 2025-05-23 04:56 More information about USE flags

The X USE flag sandbox replaces the regular X11 server with Xpra or Xephyr server. This prevents X11 keyboard loggers and screenshot utilities from accessing the main X11 server but introduces a lot of additional dependencies.

Emerge

root #emerge --ask sys-apps/firejail

Configuration

Firejail comes with numerous default profiles for many popular applications located in /etc/firejail/. In many cases the default profile configuration is sufficient. In addition to configuring a profile users may wish to set up a shortcut to enable firejail to be run by default for their selected application.

Profiles

The list of preconfigured profiles is available in /etc/firejail/.

If you wish to make customizations for an existing profile simply copy it to your home directory and edit as necessary:

user $cp /etc/firejail/firefox.profile ~/.config/firejail/firefox.profile

To make a profile for an application without a preconfigured profile you can use the default profile as a basis:

user $cp /etc/firejail/default.profile ~/.config/firejail/app-name.profile

Here are some example options you may wish to include in a custom profile:

FILE ~/.config/firejail/app-name.configCustom profile example

whitelist ~/pictures/

whitelist ~/share/
read-only ~/share/

whitelist ~/dev/WebExtensions/
read-only ~/dev/WebExtensions/

whitelist ~/.cache/fish/

blacklist /mnt
blacklist /opt

Using Firejail by default

A symbolic link to /usr/bin/firejail under the name of a program, will start the program in Firejail sandbox. A good place is /usr/local/bin directory. For example to run Firefox with firejail by default:

root #ln -s /usr/bin/firejail /usr/local/bin/firefox

This works for clicking on desktop environment icons, menus etc. Use firejail --tree to verify the program is sandboxed.

user $firejail --tree

23615:larry:firejail /usr/bin/firefox 
  23616:larry:firejail /usr/bin/firefox 
    23618:larry:/usr/bin/firefox

Alternatively you can create the following file instead and make it executable:

FILE /usr/local/bin/firefoxFirejail Desktop Integration

#!/bin/bash
firejail /usr/bin/firefox $@

This method allows command line options to be passed to firejail. Remember to make it executable with chmod +x /usr/local/bin/firefox.

To use Firejail by default for all applications for which it has profiles, run the firecfg tool as root.

root #firecfg

Important
In the default configuration, firecfg will build a symbolic link for patch, this action will make portage work incorrectly , maybe you need to remove the link or do some configurations for patch

System-wide Configuration

System-wide configuration is set in /etc/firejail/firejail.config. If you have executables in /usr/local/bin corresponding to one of your firejailed applications combined with the private-bin profile option then make sure private-bin-no-local is set to yes

FILE /etc/firejail/firejail.configSystem-wide settings example

# Remove /usr/local directories from private-bin list, default disabled.
private-bin-no-local yes

Kernel

Optionally you can enable user namespaces in the kernel so they can be utilized by firejail:

KERNEL Enabling user namespaces

General setup --->
  Namespaces support --->
    <*>  User namespace

Usage

Usage is simple as:

user $firejail firefox

Private mode can be used as a quick way of hiding all the files in your home directory from sandboxed programs. It is enabled using --private command line option:

user $firejail --private firefox

Additionally, firejail can provide full graphical isolation for X11-based programs like firefox; an in-depth tutorial for doing so may be read here.

Troubleshooting

firemon

Firejail comes with a tool firemon which can be used to help with troubleshooting. To use it run firemon as root then in a separate terminal start the application you wish to troubleshoot with firejail application.

Verbose arguments

Consider to use following arguments:

--trace --debug-caps --debug-errnos --debug-syscalls --debug-protocols --debug-blacklists --debug-whitelists --debug-caps --debug-errnos --debug-private-lib --debug-protocols --debug-syscalls

Possible obstacles

not all executables from --private-bin list were found.

Either disable the private-bin option in your application profile or ensure private-bin-no-local yes is set in /etc/firejail/firejail.config.

user namespaces not available in the current kernel.

Make sure user namespaces are set in the kernel. CONFIG_USER_NS=y

External resources