Routing and DNS setting

Trying to use example in legato documentation for interface settings : https://docs.legato.io/16_10/c_mdcDataSessions.html

No way to write in file /etc/resolv.conf having permission denied error.

I did add /etc/resolv.conf in the requires/file section in the adef of the project .

Only solution was to set sandboxed option to false.

What was wrong?

Is there a best way to change the routing than having a system call?

Regards