Warning: This program is experimental and its interface is subject to change.


nix log - show the build log of the specified packages or paths, if available


nix log [option...] installable


  • Get the build log of GNU Hello:

    # nix log nixpkgs#hello
  • Get the build log of a specific store path:

    # nix log /nix/store/lmngj4wcm9rkv3w4dfhzhcyij3195hiq-thunderbird-52.2.1
  • Get a build log from a specific binary cache:

    # nix log --store https://cache.nixos.org nixpkgs#hello


This command prints the log of a previous build of the derivation installable on standard output.

Nix looks for build logs in two places:

  • In the directory /nix/var/log/nix/drvs, which contains logs for locally built derivations.

  • In the binary caches listed in the substituters setting. Logs should be named <cache>/log/<base-name-of-store-path>, where store-path is a derivation, e.g. https://cache.nixos.org/log/dvmig8jgrdapvbyxb1rprckdmdqx08kv-hello-2.10.drv. For non-derivation store paths, Nix will first try to determine the deriver by fetching the .narinfo file for this store path.


  • --debugger
    start an interactive environment if evaluation fails

Common evaluation options:

  • --arg name expr
    Pass the value expr as the argument name to Nix functions.

  • --argstr name string
    Pass the string string as the argument name to Nix functions.

  • --eval-store store-url
    The Nix store to use for evaluations.

  • --impure
    Allow access to mutable paths and repositories.

  • --include / -I path
    Add path to the list of locations used to look up <...> file names.

  • --override-flake original-ref resolved-ref
    Override the flake registries, redirecting original-ref to resolved-ref.

Common flake-related options:

  • --commit-lock-file
    Commit changes to the flake's lock file.

  • --inputs-from flake-url
    Use the inputs of the specified flake as registry entries.

  • --no-registries
    Don't allow lookups in the flake registries. This option is deprecated; use --no-use-registries.

  • --no-update-lock-file
    Do not allow any updates to the flake's lock file.

  • --no-write-lock-file
    Do not write the flake's newly generated lock file.

  • --override-input input-path flake-url
    Override a specific flake input (e.g. dwarffs/nixpkgs). This implies --no-write-lock-file.

  • --recreate-lock-file
    Recreate the flake's lock file from scratch.

  • --update-input input-path
    Update a specific flake input (ignoring its previous entry in the lock file).

Options that change the interpretation of installables:

  • --derivation
    Operate on the store derivation rather than its outputs.

  • --expr expr
    Interpret installables as attribute paths relative to the Nix expression expr.

  • --file / -f file
    Interpret installables as attribute paths relative to the Nix expression stored in file. If file is the character -, then a Nix expression will be read from standard input. Implies --impure.