| RUMPFS(4) | Device Drivers Manual | RUMPFS(4) | 
rumpfs —
rumpfs is a simple in-memory file system for rump
  kernels. It is automatically mounted as the root file system of a rump kernel
  at boot time, provided that the VFS faction is configured into the rump kernel
  instance.
The three main features of rumpfs are:
rumpfs is not intended for hosting large
    files or big directory hierarchies. If faced with such a use case, mounting
    a tmpfs file system inside the rump kernel is recommended.
rumpfs first appeared in NetBSD
  6.0.
| March 3, 2014 | NetBSD 9.4 |