[lxc-users] creating device nodes in unprivileged containers?

[Tomasz Chmielewski]

In an unprivileged Ubuntu 14.04 container, I'm trying to run a program 
which needs to create device nodes.

Unfortunately it fails:

# pbuilder-⁠dist trusty i386 create
W: /⁠root/⁠.pbuilderrc does not exist
I: Logging to /⁠root/⁠pbuilder/⁠trusty-⁠i386_result/⁠last_operation.log
I: Distribution is trusty.
I: Current time: Wed Jul  1 07:25:49 UTC 2015
I: pbuilder-⁠time-⁠stamp: 1435735549
I: Building the build environment
I: running debootstrap
/⁠usr/⁠sbin/⁠debootstrap
mknod: '/var/cache/pbuilder/build/5377/./test-dev-null': Operation not 
permitted
E: Cannot install into target '/var/cache/pbuilder/build/5377/.' mounted 
with noexec or nodev
E: debootstrap failed
W: Aborting with an error
I: cleaning the build env
I: removing directory /var/cache/pbuilder/build//5377 and its 
subdirectories


So I've tried to add the following to container's config:

lxc.cap.keep = CAP_MKNOD

However, the container fails to start:

lxc-start 1435737618.188 ERROR    lxc_conf - conf.c:lxc_setup:3925 - 
Simultaneously requested dropping and keeping caps


I don't see "mknod" dropped before in included configs:

# grep -ri mknod /usr/share/lxc/config/*



How can I let create custom device nodes?

The host is running these versions:

# dpkg -l|grep lxc
ii  liblxc1                                  
1.1.2-0ubuntu3~ubuntu14.04.1~ppa1    amd64        Linux Containers 
userspace tools (library)
ii  lxc                                      
1.1.2-0ubuntu3~ubuntu14.04.1~ppa1    amd64        Linux Containers 
userspace tools
ii  lxc-templates                            
1.1.2-0ubuntu3~ubuntu14.04.1~ppa1    amd64        Linux Containers 
userspace tools (templates)
ii  lxcfs                                    
0.9-0ubuntu1~ubuntu14.04.1~ppa1      amd64        FUSE based filesystem 
for LXC
ii  python3-lxc                              
1.1.2-0ubuntu3~ubuntu14.04.1~ppa1    amd64        Linux Containers 
userspace tools (Python 3.x bindings)


-- 
Tomasz Chmielewski
http://wpkg.org