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[GH-ISSUE #3066] Monitor network connection attempts with firejail/firemon #1919

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opened 2026-05-05 08:35:19 -06:00 by gitea-mirror · 3 comments

gitea-mirror commented

2026-05-05 08:35:19 -06:00

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Originally created by @curioustwo on GitHub (Nov 27, 2019).
Original GitHub issue: https://github.com/netblue30/firejail/issues/3066

Hi,
Is it possible to monitor outgoing network connections with either firejail or firemon? I would like to know which network connections an application is trying to make when it is "firejail'ed".

Thanks!

Originally created by @curioustwo on GitHub (Nov 27, 2019). Original GitHub issue: https://github.com/netblue30/firejail/issues/3066 Hi, Is it possible to monitor outgoing network connections with either firejail or firemon? I would like to know which network connections an application is trying to make when it is "firejail'ed". Thanks!

gitea-mirror

2026-05-05 08:35:19 -06:00

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gitea-mirror commented

2026-05-05 08:35:22 -06:00

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@netblue30 commented on GitHub (Nov 29, 2019):

It is quite easy, but you have to start the sandbox with a network namespace (--net). For example:

$ firejail --name=mybrowser --net=eth0 firefox

Then, you open a new terminal and join the network namespace with some network monitor such as tcpdump:

$ sudo firejail --join-network=mybrowser tcpdump

The command runs as root (sudo).

You can also try wireshark. It used to work for me on the old Debian, but on the new one it doesn't. I guess it has to do with the way they set up X11, so I get something like:

~$ sudo firejail --join-network=mybrowser wireshark
Switching to pid 9548, the first child process inside the sandbox
Child process initialized in 8.57 ms
No protocol specified
qt.qpa.screen: QXcbConnection: Could not connect to display :0.0
Could not connect to any X display.

@netblue30 commented on GitHub (Nov 29, 2019): It is quite easy, but you have to start the sandbox with a network namespace (--net). For example: ````` $ firejail --name=mybrowser --net=eth0 firefox ````` Then, you open a new terminal and join the network namespace with some network monitor such as tcpdump: ````` $ sudo firejail --join-network=mybrowser tcpdump ````` The command runs as root (sudo). You can also try wireshark. It used to work for me on the old Debian, but on the new one it doesn't. I guess it has to do with the way they set up X11, so I get something like: ````` ~$ sudo firejail --join-network=mybrowser wireshark Switching to pid 9548, the first child process inside the sandbox Child process initialized in 8.57 ms No protocol specified qt.qpa.screen: QXcbConnection: Could not connect to display :0.0 Could not connect to any X display. `````

gitea-mirror commented

2026-05-05 08:35:23 -06:00

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@rusty-snake commented on GitHub (Jan 17, 2020):

@curioustwo
I'm closing here due to inactivity, please fell free to reopen if you have more questions.

@rusty-snake commented on GitHub (Jan 17, 2020): @curioustwo I'm closing here due to inactivity, please fell free to reopen if you have more questions.

gitea-mirror commented

2026-05-05 08:35:25 -06:00

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@curioustwo commented on GitHub (Jan 26, 2020):

I had a follow-up question. To do this without having the APP access Internet at all I would have to create a virtual eth interface or something? I want to monitor the attempts but not let it go through....

@curioustwo commented on GitHub (Jan 26, 2020): I had a follow-up question. To do this without having the APP access Internet at all I would have to create a virtual eth interface or something? I want to monitor the attempts but not let it go through....

gitea-mirror referenced this issue

2026-05-05 10:14:18 -06:00

[PR #1919] [MERGED] Add --keep-var-tmp and associated profile option #4129

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Reference: github-starred/firejail#1919

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