Yes. A Linux app can use a route or resolver outside the one you intended, and a system-wide VPN or Tor setup does not by itself prove that every program is protected. oniux is an experimental Linux command-line tool that isolates a selected application in kernel namespaces and gives it a Tor-backed network path. It can reduce ordinary route and DNS escape paths for that process, but it cannot prevent every leak—especially when the app hands work to a helper process running outside its isolated environment.
What oniux does—and what it does not do
The Tor Project describes oniux as “a tool that utilizes various Linux namespaces(7) in order to isolate an arbitrary application over the Tor network.” It is designed for per-application routing: you launch a chosen command with oniux, rather than assuming every process on the computer will use Tor.
oniux uses onionmasq to provide a TUN device for Tor traffic. The selected process runs in a separate network namespace with its own network environment and resolver configuration. That helps reduce the chance that ordinary network traffic or DNS lookups from that process use the host’s normal route. It is not a system-wide VPN, a guarantee of anonymity, or protection for applications you did not launch through oniux.
How the isolation works
According to the project README, oniux creates a child process with clone(2) in its own network, mount, PID, and user namespaces. It mounts a private /proc, maps the caller’s UID and GID, and bind-mounts a temporary nameserver configuration over /etc/resolv.conf. It then creates an onion0 TUN interface and passes the TUN file descriptor to the parent through a Unix-domain socket. The requested command runs after capabilities acquired in the user namespace are dropped.
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In practical terms, the isolated app gets a separate network stack and resolver setup intended to send its traffic over Tor. The resolver change is relevant to DNS-leak concerns: it changes the resolver configuration visible inside that namespace, rather than merely intercepting some application library calls. This reduces common escape paths, but does not prove that an app or a helper it contacts cannot send data elsewhere.
Build and run one command through oniux
The project’s documented quick-start path builds oniux with Cargo, then prefixes the command you want to run. The example below uses curl to visit Tor Project’s check page:
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- Install or otherwise make available Rust and Cargo, then obtain the oniux project source from the Tor Project repository.
- From the project directory, build the debug binary with
cargo build. - Run the desired command through the newly built binary:
./target/debug/oniux curl https://check.torproject.org.
The README says the Linux tun kernel module is required. It is normally loaded on most distributions. If oniux reports that the required file is missing, the documented remedy is to load the module with modprobe tun, then retry the command. Loading a kernel module may require administrator privileges.
oniux versus torsocks
The Tor Project characterizes the main distinction as kernel namespace isolation with onionmasq for oniux, versus LD_PRELOAD-based interception for torsocks. These approaches have different failure modes; neither should be treated as a universal fix for all apps.
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|---|---|---|
| Isolation boundary | Runs the selected command in Linux namespaces with a Tor-backed TUN path. | Uses an LD_PRELOAD interception approach, as described by the Tor Project. |
| What it can help address | Provides a separate network environment and resolver configuration for the selected process, reducing ordinary route and DNS escape paths. | Interception depends on the application and its networking behavior; the cited project comparison does not establish a comparable private namespace or resolver setup. |
| Compatibility considerations | Application behavior still matters; not every URL mode or app is guaranteed to work. | Library interception can be a poor fit for unusual networking code. The project says oniux makes leaking harder than torsocks, but is not immune. |
| Processes outside the selected command | A helper or server outside the namespace can still make a connection on the app’s behalf if the app communicates with it. | Because protection relies on interception in the process, behavior involving other processes also needs scrutiny; the cited project comparison does not provide a blanket guarantee. |
The README’s warning is explicit: “While oniux makes it harder for an application to leak than torsocks, it does not mean oniux is immune to it.” The namespace boundary is a stronger isolation mechanism than relying only on library interception, but choosing oniux does not remove the need to consider how a particular application is built and used.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Important limits: helper processes and application behavior
Unix sockets can hand work to an outside process
Isolation cannot block every form of interprocess communication while remaining usable. The README gives an example involving an Emacs client that connects to an Emacs server through a Unix-domain socket. If that server runs outside oniux’s namespace, it can make the network connection itself. The client may therefore appear isolated while the process doing the networking is not.
For an app that uses background services, browser helpers, local daemons, or an existing server process, check whether the network request is made by the process launched under oniux or by another process. If the latter is outside the namespace, oniux cannot force that other process’s traffic through its Tor interface merely because the client was launched with oniux.
Successful launch does not establish universal compatibility
Application-level rules can affect what works through Tor. For example, a curl issue opened on 15 May 2025 reports that curl rejects a .onion URL with “Not resolving .onion address (RFC 7686)” when run through oniux. That report describes curl’s handling of the URL, not proof that oniux’s namespace failed. Test the exact application and URL type you intend to use; a working ordinary HTTPS request does not establish that every protocol or address format will work.
Quick Recap
When oniux is a reasonable choice
- Use it when you want to launch a specific Linux command with a separate Tor-oriented network environment, rather than route the whole host.
- Confirm that the command itself performs the network activity; account for helper processes and servers that may run outside the namespace.
- Check the exact application behavior and address type, particularly if using a feature such as
.onionURLs. - Treat it as experimental software and a risk-reduction measure, not as a guarantee that no data can escape.
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