Can't get minijail0 working without bind-mounting /

Can't get minijail0 working without bind-mounting /

[Demi Marie Obenour]

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I'm trying to get minijail0 to work without bind-mounting /, and I'm
running into lots of problems.  So far:

- Unprivileged user namespaces fail due to -EPERM in a mount syscall.

- Mounting a tmpfs over / always causes the program to be executed
  to not be found.

- `sudo ./minijail0.sh -v --profile=minimalistic-mountns /bin/ls`
  works, but doesn't actually do any sandboxing as it bind-mounts `/`.

Are there examples of how to use minijail0 properly?  Alternatively,
can I use it purely for seccomp and Landlock, and use bubblewrap to
handle namespacing?
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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Re: Can't get minijail0 working without bind-mounting /

[Demi Marie Obenour]

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On 11/23/25 01:38, Demi Marie Obenour wrote:
> I'm trying to get minijail0 to work without bind-mounting /, and I'm
> running into lots of problems.  So far:
> 
> - Unprivileged user namespaces fail due to -EPERM in a mount syscall.
> 
> - Mounting a tmpfs over / always causes the program to be executed
>   to not be found.
> 
> - `sudo ./minijail0.sh -v --profile=minimalistic-mountns /bin/ls`
>   works, but doesn't actually do any sandboxing as it bind-mounts `/`.
> 
> Are there examples of how to use minijail0 properly?  Alternatively,
> can I use it purely for seccomp and Landlock, and use bubblewrap to
> handle namespacing?

Forwarding to minijail mailing list.  The first message was rejected
for some reason.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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Re: [minijail] Re: Can't get minijail0 working without bind-mounting /

[Mike Frysinger]

On Mon, Nov 24, 2025 at 1:57 PM Demi Marie Obenour wrote:
> On 11/23/25 01:38, Demi Marie Obenour wrote:
> > I'm trying to get minijail0 to work without bind-mounting /, and I'm
> > running into lots of problems.  So far:
> >
> > - Unprivileged user namespaces fail due to -EPERM in a mount syscall.

those errors come from the kernel, not minijail.  you prob want to
double check user namespaces constraints.

> > - Mounting a tmpfs over / always causes the program to be executed
> >   to not be found.

what is the command line you are using exactly, and is the program
you're trying to run statically or dynamically linked ?

> > - `sudo ./minijail0.sh -v --profile=minimalistic-mountns /bin/ls`
> >   works, but doesn't actually do any sandboxing as it bind-mounts `/`.

it sounds like you're conflating "empty filesystem" with "it's
sandboxed".  sandboxing (namespaces / container technology) is
composed of a multitude of layers.

what you describe here is correct.  check the set of mounts inside
that sandbox to see they're significantly reduced.

> > Are there examples of how to use minijail0 properly?

seems like you've already found some, and they're working correctly.
the website also links to more docs & practical examples.
https://google.github.io/minijail/

> > Alternatively,
> > can I use it purely for seccomp and Landlock, and use bubblewrap to
> > handle namespacing?

if the minijail config allows access to all the syscalls/privileges
that the program needs to set things up, then i don't see why not.
-mike