How to get new pid of sandbox?

[rieje]

When I run weechat in a sandbox, its FIFO pipe is /run/user/1000/weechat/weechat_fifo_9 where its FIFO pipe is in the format /run/user/1000/weechat/weechat_fifo_<$PID>. How can I get this PID of 9 for this process? firejail --list doesn't show this. I need it to get a predictable path for FIFO (weechat does not expose a way to configure this as a command line argument).

[glitsj16]

Have you tried firejail --tree yet to check if that shows what you need?

Alternatively, use a shell script:

#!/bin/sh
until _fifo="$(find "$XDG_RUNTIME_DIR" -maxdepth 1 -type p -name "weechat*")" > /dev/null; do
    sleep 0.5
done
# show me the FIFO
echo "$_fifo"
# run a weechat command
echo "foo" > "$_fifo" &

[rusty-snake]

grep NStgid /proc/<PID>/status should show NStgid: <PID> 9.

And see https://blogs.oracle.com/linux/post/translating-process-id-between-namespaces