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nix-build release.nix -A deb_ubuntu1604x86_64
these derivations will be built:
  /nix/store/2xwc3nfmgbz63x2lvrmayb6rlsz3kx5z-ubuntu-16.04-xenial-amd64.drv
  /nix/store/q9wyj7kjrn3d1yka9yq94dkn93fi6y6h-nix-deb-ubuntu-16.04-xenial-amd64-1.12pre1234.abcdef.drv
building path(s) ‘/nix/store/bsnm6pzwxppz1mv3gja9hmm1zlj20d59-ubuntu-16.04-xenial-amd64’
Formatting '/nix/store/bsnm6pzwxppz1mv3gja9hmm1zlj20d59-ubuntu-16.04-xenial-amd64/disk-image.qcow2', fmt=qcow2 size=4294967296 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
Could not access KVM kernel module: Permission denied
failed to initialize KVM: Permission denied
builder for ‘/nix/store/2xwc3nfmgbz63x2lvrmayb6rlsz3kx5z-ubuntu-16.04-xenial-amd64.drv’ failed with exit code 1
cannot build derivation ‘/nix/store/q9wyj7kjrn3d1yka9yq94dkn93fi6y6h-nix-deb-ubuntu-16.04-xenial-amd64-1.12pre1234.abcdef.drv’: 1 dependencies couldn't be built
error: build of ‘/nix/store/q9wyj7kjrn3d1yka9yq94dkn93fi6y6h-nix-deb-ubuntu-16.04-xenial-amd64-1.12pre1234.abcdef.drv’ failed