Please read the common steps first.
udocker is not Docker.
udocker provides four modes for running containers as a non-root user:
- Pn: Proot mode
- Fn: fakechroot mode
- Rn: rootless runc mode
- Sn: Singularity (now called Apptainer) mode
The third mode (Rn) falls into the scope of Rootless Containers, and the fourth mode (Sn) also does when it runs in non-setuid mode, but the others do not: Pn and Fn are not containers (in our view).
For futher information, see https://github.com/indigo-dc/udocker/