I have a program I would like to test in offline mode without taking down my actual network. This program would still need to connect to local sockets, including unix domain sockets and loopback. It also needs to listen on loopback and be visible to other apps.
But attempts to connect to a remote machine should fail.
I'd like to have a utility that works like
sudo and simply runs a command with the Internet (and LAN) concealed and everything else still working:
$ offline my-program-to-test
This question has hints at the answer: Block network access of a process?
There are a couple of suggestions there, such as run as another user then manipulate iptables, or
unshare -n. But in both cases I don't know the incantation to get unix domain sockets and loopback to be shared with the main system - the answers to that question only tell me how to unshare the entire network.
The program I'm testing still needs to connect to my X server and dbus and even be able to listen on loopback for connections from other apps on the system.
Ideally I'd like to avoid creating chroots or users or VMs or the like, since it becomes just as annoying as unplugging the network cable is. i.e. the point of the question is how can I make this as simple as a
I'd love the process to run 100% normally except that network calls specifying a non-local address would fail. Ideally keeping the same uid, same homedir, same pwd, same everything except ... offline.
I'm using Fedora 18, so unportable Linux answers are just fine (expected, even).
I'm even happy to solve this by writing a C program, if that's what's involved, so answers that involve writing C are fine. I just don't know what syscalls that C program would need to make to revoke the external network access while keeping local network.
Any developer trying to support "offline mode" would probably appreciate this utility!