anchor.diff:  
       [nixstore]
       path = /nix/store
  -    read only = no
  +    writable = yes
       guest ok = yes
   
       [xchg]
       path = /xchg
  -    read only = no
  +    writable = yes
       guest ok = yes
       CONFIG
   
  
positive.code:     [global]
      security = user
      map to guest = Bad User
      workgroup = cygwin
      netbios name = controller
      server string = %h
  
negative.code:       -o trans=virtio,version=9p2000.L,msize=262144,cache=loose \
        xchg /fs/xchg
  
      echo root:x:0:0::/root:/bin/false > /fs/etc/passwd
  
      set +e
      chroot /fs $command $out
  