Learn how to avoid LXC errors when creating new unprivileged containers. Our LXC/LXD Support team is here to help you with your questions and concerns.

LXC Error When Creating New Unprivileged Containers

Did you know that when LXC fails to create an “unprivileged container,” it is due to an issue with setting up a container where the root user inside is mapped to a non-privileged user on the host machine?

According to our experts, this mapping prevents the container from performing sensitive actions requiring root access to the host while offering isolation and security benefits. In short, the container creation fails due to insufficient permissions or an incorrect configuration for running a container without full host privileges.

Causes Behind the Error

• The issue can be due to the kernel provided with the operating system. It may lack several necessary features, including those required by LXC.
• A common cause of this problem is insufficient permissions related to the user namespace settings. Therefore, we need to verify kernel configurations and permissions.

Solution

1. First, run the following command to check the kernel settings:

   # cat /proc/sys/kernel/unprivileged_userns_clone
2. If the result is `0`, we have to make these changes:

   
# echo "kernel.unprivileged_userns_clone=1" > /etc/sysctl.d/80-lxc-userns.conf
# sysctl --system


If the above solution does not work, remove the file `/etc/sysctl.d/80-lxc-userns.conf` and run `sysctl –system` again to revert the changes.

If we encounter an error like “Your system is not configured with suburbs,” it means we are trying to create an unprivileged container without properly configuring subUIDs.

Here’s how you can configure them for Ubuntu 14.04:

1. Create the configuration directory for LXC:

   $ mkdir -p ~/.config/lxc
2. Add the necessary configuration lines:

   
$ echo "lxc.id_map = u 0 100000 65536" > ~/.config/lxc/default.conf
$ echo "lxc.id_map = g 0 100000 65536" >> ~/.config/lxc/default.conf
$ echo "lxc.network.type = veth" >> ~/.config/lxc/default.conf
$ echo "lxc.network.link = lxcbr0" >> ~/.config/lxc/default.conf

3. Add user permissions:

   echo "$USER veth lxcbr0 2" | sudo tee -a /etc/lxc/lxc-usernet
4. After configuring these settings, we should be able to create an Ubuntu container with:

   $ lxc-create -t download -n u1 -- -d ubuntu -r trusty -a amd64

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Conclusion

Setting up unprivileged containers in LXC requires careful configuration of user namespaces, permissions, and system settings. By making sure that subUIDs and subGIDs are properly allocated, creating the necessary configuration files, verifying kernel settings, and running commands as a non-root user, we can resolve issues related to creating unprivileged containers in LXC.

In brief, our Support Experts demonstrated how to avoid LXC errors when creating new unprivileged containers.