nix build -f '<nixpkgs/nixos>'
             config.system.build.toplevel
warning: Nix search path entry '$HOME/.nix-defexpr/channels' does not exist, ignoring
builder for '/nix/store/qj5vz8bkkksmjajnr361rzn6kca8pga0-nixos-boot-disk.drv' failed with exit code 1; last 3 log lines:
  Formatting '/nix/store/1p5zizn43iafy0vgwd3k5dibl6qrnjch-nixos-boot-disk/disk.img', fmt=qcow2 size=41943040 cluster_size=65536 lazy_refcounts=off refcount_bits=16
  QEMU 2.12.0 monitor - type 'help' for more information
  (qemu) qemu-system-x86_64: -serial pty: char device redirected to /dev/pts/0 (label serial0)
cannot build derivation '/nix/store/901lv6h54p9j1bmx9f3vq8yp6snp1s2b-run-nixos-vm.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/k9ck19rdrk970f6j7k2g3aw78i8g718j-nixos-vm.drv': 1 dependencies couldn't be built
[53 built (1 failed), 17 copied (139.3 MiB), 29.7 MiB DL]
error: build of '/nix/store/k9ck19rdrk970f6j7k2g3aw78i8g718j-nixos-vm.drv' failed
config.system.build.toplevel: command not found