Firejail is a SUID sandbox program that reduces the risk of security breaches by restricting the running environment of untrusted applications using Linux namespaces. It currently implements hostname, filesystem, PID, IPC, and networking stack isolation, and it runs on any recent Linux system. It includes a sandbox profile for Mozilla Firefox. Firejail also expands the restricted shell facility found in bash by adding Linux namespace support. It supports sandboxing specific users upon login. The software also includes a small monitoring utility, firemon.