ExecWithFakeroot will exec singularity with provided args, in a subuid/gid-mapped fakeroot user namespace.

Getgid retrieves the uid stored in the env var _CONTAINERS_ROOTLESS_GID, or the current egid if the env var is not set.

Getuid retrieves the uid stored in the env var _CONTAINERS_ROOTLESS_UID, or the current euid if the env var is not set.

GetUser retrieves the User struct for the uid stored in the env var _CONTAINERS_ROOTLESS_UID, or the current euid if the env var is not set.

InNS returns true if we are in a namespace created using this package.

RunInMountNS will run singularity with provided args, in a mount namespace only.