Extend Sysbox support to RPM camp (Redhat, Centos, Fedora)

[rodnymolina]

Sysbox is currently only supported in Ubuntu distribution. Our goal is to make Sysbox a distro-agnostic runtime, but for that to happen these distributions must be capable of running relatively-recent kernels, so that Sysbox's kernel dependencies can be met.

In Fedora's case (> 31) these dependencies are already satisfied (>= kernel 5.5); however, in CentOS and Redhat we may need to wait a bit longer (unless a user is willing to upgrade kernel w/o vendor support).

Leaving kernel compatibility aside, our goal with this EPIC is to keep track of the overall implementation effort that needs to be carried out for Sysbox to support these distributions.

[ctalledo]

With PR #127, Sysbox now supports distros such as RedHat/Fedora, CentOS, and Debian.

However, we don't yet have package installer for these distros. As a result, you must build Sysbox from source to run on these distros.

In addition, these distros do not support shiftfs (unlike Ubuntu), so using Sysbox there requires that the container manager above be configured with user-namespaces (e.g., Docker must be configured with userns-remap).

See the Sysbox Distro Compat Doc for more info.

In the near future we will work on having packaged versions of Sysbox for these distros.

[ctalledo]

In addition, these distros do not support shiftfs (unlike Ubuntu), so using Sysbox there requires that the container manager above be configured with user-namespaces (e.g., Docker must be configured with userns-remap).

FYI, I tried installing the shiftfs-dkms (out-of-tree kernel module) into a Fedora-32 kernel, and while I was able to compile and install the module into the kernel, creating shiftfs mounts failed with "operation not permitted".

This needs more investigation. If we can get shiftfs-dkms working on Fedora/CentOS, it would be helpful for users that want to use Sysbox in those distros yet don't want to configure Docker in userns-remap mode.

Another thing that comes to mind, is that overlayfs requires a patch in order for shiftfs mounts to be done on top of it. Last time I checked, only Ubuntu kernels carried that patch, though this could have changed recently.