O Ubuntu 16.04 tem firejail version 0.9.38.10
e o Ubuntu 18.04 tem firejail version 0.9.52
. Veja notas de lançamento: link dizem, por 0.9.52
(entre outras coisas)
- feature: --rlimit-as
firejail (0.9.56-LTS)
entrada tem
- command line options removed: ..., --rlimit*, ...
ainda no momento em que link lista-os.
O leiame de firejail
diz sobre o "ramo" de LTS
We are rebasing our Long Term Support branch of Firejail. The current LTS version (0.9.38.x) is more than two years old. The new version updates the code base to 0.9.56. We target a reduction of approx. 40% of the code by removing rarely used features (chroot, overlay, rlimits, cgroups), incomplete features (private-bin, private-lib), and a lot of instrumentation (build profile feature, tracing, auditing, etc).
Então você precisa ter cuidado com a versão que você instalou!