Option --quiet suppresses important warnings

[rdiez]

Option --quiet is simply documented as follows: Turn off Firejail's output.

Without this option, Firejail is too verbose:
------8<------8<------8<------
$ firejail --noprofile sh -c "echo a"

^[]0;firejail sh -c echo a ^Ga
Parent pid 21368, child pid 21369

Parent is shutting down, bye...
------8<------8<------8<------

Note the "^[]0;" at the beginning: Those are escape characters for some terminal. And the same with "^Ga" at the end.

Firejail should at least check whether STDOUT is a terminal before outputting such colour or terminal codes. Otherwise, the output looks weird in a log file.

Other tools like Git offer more control, see for example:
git -c color.ui=always status

I am using Ubuntu 18.04.4 LTS, which comes with Firejail version 0.9.52, a rather old version indeed. So maybe this has already been improved.

In any case, because the output looks ugly, I started using --quiet . The trouble is, Firejail stops outputting warnings like these:

Warning: you are not allowed to change /tmp to read-write
Warning: cannot create a new user namespace, going forward without it...

If some option is not working correctly, and you specified --quiet , you may never realise. Firejail needs an option to suppress unnecessary banners, echoing the command to run, and otherwise unimportant information, but such warnings should still be output.

[glitsj16]

You can get the latest stable release from the firejail PPA. I'm not implying that there isn't any room for improvement with regards to firejail's verbosity/error handling, but it would be handy if you can confirm these issues are still present on the latest stable release.

[rdiez]

I have created a separate issue #3356 for the terminal control codes.

[rdiez]

As requested, I have tested the following with the latest Firejail release version 0.9.62. I am using Ubuntu 18.04.4 LTS, so that new version came from the mentioned PPA.

1. This command:

firejail --noprofile --read-write=/tmp sh -c "echo a"

issues warning:

Warning: you are not allowed to change /tmp to read-write

Adding option --quiet silences the warning. As I said, I think that should not happen.

2. This command:

firejail --noprofile --blacklist=/ --noroot sh -c "echo a"

issues warning:

Warning: cannot create a new user namespace, going forward without it...

Adding option --quiet silences the warning. This is more serious than case (1), because a protection is being skipped.

[rusty-snake]

quiet is for programs which can pipe data over stdout to an other program where firejails you will break.

Solutions:

1. print warnings to stderr
2. print warnings to syslog

[rdiez]

I would print warnings to stderr by default. Not many people have a habit of looking at syslog when running commands.