linux-kernel - Re: plan9 semantics on Linux

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Message-ID: <20180214045442.jyv6zpbwz5glzi4z@gordon>
Date:   Wed, 14 Feb 2018 15:54:42 +1100
From:   Aleksa Sarai <asarai@...e.de>
To:     Enrico Weigelt <lkml@...ux.net>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: plan9 semantics on Linux - mount namespaces

On 2018-02-14, Enrico Weigelt <lkml@...ux.net> wrote:
> On 13.02.2018 22:27, Aleksa Sarai wrote:
> 
> > You can do this by creating a new user namespace (CLONE_NEWUSER), which
> > then gives you the required permissions to create other namespaces
> > (CLONE_NEWNS). This is how "rootless containers" or unprivileged
> > containers operate.
> 
> hmm, unshare -U doesn't work for me (even as root). But docker works,
> so user namespaces should be working. Any idea what could be wrong ?

It depends how old your kernel is and what distro you use. Arch Linux
disables user namespaces entirely, Debian requires that you set a sysctl
to enable unprivileged user namespaces, and RHEL requires you to set
both a sysctl and a kernel boot-flag. Also check how old your kernel is
(unprivileged user namespace support was added in 3.8).

Also Docker doesn't use user namespaces by default (you need to manually
enable it with --userns-remap, check the docs for more details). You
probably also want to be using "unshare -r" in your testing (as "unshare
-U" will leave you without mapped users).

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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