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nix-build(1) General Commands Manual nix-build(1) Name nix-build - build a Nix expression Synopsis nix-build [paths] [--arg name value] [--argstr name value] [{--attr | -A} attrPath] [--no-out-link] [--dry-run] [{--out-link | -o} outlink] Disambiguation This man page describes the command nix-build, which is distinct from nix build. For documentation on the latter, run nix build --help or see man nix3-build. Description The nix-build command builds the derivations described by the Nix ex- pressions in paths. If the build succeeds, it places a symlink to the result in the current directory. The symlink is called result. If there are multiple Nix expressions, or the Nix expressions evaluate to multi- ple derivations, multiple sequentially numbered symlinks are created (result, result-2, and so on). If no paths are specified, then nix-build will use default.nix in the current directory, if it exists. If an element of paths starts with http:// or https://, it is inter- preted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must include a single top-level di- rectory containing at least a file named default.nix. nix-build is essentially a wrapper around nix-instantiate <nix- instantiate.md> (to translate a high-level Nix expression to a low- level store derivation <../glossary.md#gloss-store-derivation>) and nix-store --realise <../command-ref/nix-store/realise.md> (to build the store derivation). Warning The result of the build is automatically registered as a root of the Nix garbage collector. This root disappears automatically when the result symlink is deleted or renamed. So dont rename the symlink. Options All options not listed here are passed to nix-store --realise <nix- store/realise.md>, except for --arg and --attr / -A which are passed to nix-instantiate <nix-instantiate.md>. • --no-out-link <#opt-no-out-link> Do not create a symlink to the output path. Note that as a result the output does not become a root of the garbage collector, and so might be deleted by nix-store --gc. • --dry-run <#opt-dry-run> Show what store paths would be built or downloaded. • --out-link <#opt-out-link> / -o outlink Change the name of the symlink to the output path created from re- sult to outlink. Special exit codes for build failure 1xx status codes are used when requested builds failed. The following codes are in use: • 100 Generic build failure The builder process returned with a non-zero exit code. • 101 Build timeout The build was aborted because it did not complete within the speci- fied timeout. • 102 Hash mismatch The build output was rejected because it does not match the out- putHash attribute of the derivation <../language/advanced-attrib- utes.md>. • 104 Not deterministic The build succeeded in check mode but the resulting output is not binary reproducible. With the --keep-going flag it's possible for multiple failures to oc- cur. In this case the 1xx status codes are or combined using bitwise OR <https://en.wikipedia.org/wiki/Bitwise_operation#OR>. 0b1100100 ^^^^ |||`- timeout ||`-- output hash mismatch |`--- build failure `---- not deterministic Common Options Most Nix commands accept the following command-line options: • --help <#opt-help> Prints out a summary of the command syntax and exits. • --version <#opt-version> Prints out the Nix version number on standard output and exits. • --verbose <#opt-verbose> / -v Increases the level of verbosity of diagnostic messages printed on standard error. For each Nix operation, the information printed on standard output is well-defined; any diagnostic information is printed on standard error, never on standard output. This option may be specified repeatedly. Currently, the following verbosity levels exist: • 0 Errors only Only print messages explaining why the Nix invocation failed. • 1 Informational Print useful messages about what Nix is doing. This is the default. • 2 Talkative Print more informational messages. • 3 Chatty Print even more informational messages. • 4 Debug Print debug information. • 5 Vomit Print vast amounts of debug information. • --quiet <#opt-quiet> Decreases the level of verbosity of diagnostic messages printed on standard error. This is the inverse option to -v / --verbose. This option may be specified repeatedly. See the previous verbosity levels list. • --log-format <#opt-log-format> format This option can be used to change the output of the log format, with format being one of: • raw This is the raw format, as outputted by nix-build. • internal-json Outputs the logs in a structured manner. Warning While the schema itself is relatively stable, the format of the error-messages (namely of the msg-field) can change be- tween releases. • bar Only display a progress bar during the builds. • bar-with-logs Display the raw logs, with the progress bar at the bottom. • --no-build-output <#opt-no-build-output> / -Q By default, output written by builders to standard output and stan- dard error is echoed to the Nix command's standard error. This op- tion suppresses this behaviour. Note that the builder's standard output and error are always written to a log file in pre- fix/nix/var/log/nix. • --max-jobs <#opt-max-jobs> / -j number Sets the maximum number of build jobs that Nix will perform in par- allel to the specified number. Specify auto to use the number of CPUs in the system. The default is specified by the max-jobs con- figuration setting, which itself defaults to 1. A higher value is useful on SMP systems or to exploit I/O latency. Setting it to 0 disallows building on the local machine, which is useful when you want builds to happen only on remote builders. • --cores <#opt-cores> Sets the value of the NIX_BUILD_CORES environment variable in the invocation of builders. Builders can use this variable at their discretion to control the maximum amount of parallelism. For in- stance, in Nixpkgs, if the derivation attribute enableParallelBuild- ing is set to true, the builder passes the -jN flag to GNU Make. It defaults to the value of the cores configuration setting, if set, or 1 otherwise. The value 0 means that the builder should use all available CPU cores in the system. • --max-silent-time <#opt-max-silent-time> Sets the maximum number of seconds that a builder can go without producing any data on standard output or standard error. The de- fault is specified by the max-silent-time configuration setting. 0 means no time-out. • --timeout <#opt-timeout> Sets the maximum number of seconds that a builder can run. The de- fault is specified by the timeout configuration setting. 0 means no timeout. • --keep-going <#opt-keep-going> / -k Keep going in case of failed builds, to the greatest extent possi- ble. That is, if building an input of some derivation fails, Nix will still build the other inputs, but not the derivation itself. Without this option, Nix stops if any build fails (except for builds of substitutes), possibly killing builds in progress (in case of parallel or distributed builds). • --keep-failed <#opt-keep-failed> / -K Specifies that in case of a build failure, the temporary directory (usually in /tmp) in which the build takes place should not be deleted. The path of the build directory is printed as an informa- tional message. • --fallback <#opt-fallback> Whenever Nix attempts to build a derivation for which substitutes are known for each output path, but realising the output paths through the substitutes fails, fall back on building the derivation. The most common scenario in which this is useful is when we have registered substitutes in order to perform binary distribution from, say, a network repository. If the repository is down, the realisa- tion of the derivation will fail. When this option is specified, Nix will build the derivation instead. Thus, installation from bi- naries falls back on installation from source. This option is not the default since it is generally not desirable for a transient failure in obtaining the substitutes to lead to a full build from source (with the related consumption of resources). • --readonly-mode <#opt-readonly-mode> When this option is used, no attempt is made to open the Nix data- base. Most Nix operations do need database access, so those opera- tions will fail. • --arg <#opt-arg> name value This option is accepted by nix-env, nix-instantiate, nix-shell and nix-build. When evaluating Nix expressions, the expression evalua- tor will automatically try to call functions that it encounters. It can automatically call functions for which every argument has a de- fault value <../language/syntax.md#functions> (e.g., { argName ? defaultValue }: ...). With --arg, you can also call functions that have arguments without a default value (or override a default value). That is, if the evaluator encounters a function with an argument named name, it will call it with value value. For instance, the top-level default.nix in Nixpkgs is actually a function: { # The system (e.g., `i686-linux') for which to build the packages. system ? builtins.currentSystem ... }: ... So if you call this Nix expression (e.g., when you do nix-env --install --attr pkgname), the function will be called automati- cally using the value builtins.currentSystem <../language/builtins.md> for the system argument. You can override this using --arg, e.g., nix-env --install --attr pkg- name --arg system \"i686-freebsd\". (Note that since the argu- ment is a Nix string literal, you have to escape the quotes.) • --arg-from-file <#opt-arg-from-file> name path Pass the contents of file path as the argument name to Nix func- tions. • --arg-from-stdin <#opt-arg-from-stdin> name Pass the contents of stdin as the argument name to Nix functions. • --argstr <#opt-argstr> name value This option is like --arg, only the value is not a Nix expression but a string. So instead of --arg system \"i686-linux\" (the outer quotes are to keep the shell happy) you can say --argstr system i686-linux. • --attr <#opt-attr> / -A attrPath Select an attribute from the top-level Nix expression being evalu- ated. (nix-env, nix-instantiate, nix-build and nix-shell only.) The attribute path attrPath is a sequence of attribute names sepa- rated by dots. For instance, given a top-level Nix expression e, the attribute path xorg.xorgserver would cause the expression e.xorg.xorgserver to be used. See nix-env --install <../command- ref/nix-env/install.md> for some concrete examples. In addition to attribute names, you can also specify array indices. For instance, the attribute path foo.3.bar selects the bar attribute of the fourth element of the array in the foo attribute of the top- level expression. • --eval-store <#opt-eval-store> store-url The URL to the Nix store <../store/types/index.md#store-url-format> to use for evaluation, i.e. where to store derivations (.drv files) and inputs referenced by them. • --expr <#opt-expr> / -E Interpret the command line arguments as a list of Nix expressions to be parsed and evaluated, rather than as a list of file names of Nix expressions. (nix-instantiate, nix-build and nix-shell only.) For nix-shell, this option is commonly used to give you a shell in which you can build the packages returned by the expression. If you want to get a shell which contain the built packages ready for use, give your expression to the nix-shell --packages convenience flag instead. • -I / --include <#opt-I> path Add an entry to the list of search paths used to resolve lookup paths <../language/constructs/lookup-path.md>. This option may be given multiple times. Paths added through -I take precedence over the nix-path configura- tion setting <../command-ref/conf-file.md#conf-nix-path> and the NIX_PATH environment variable <../command-ref/env-common.md#env- NIX_PATH>. • --impure <#opt-impure> Allow access to mutable paths and repositories. • --option <#opt-option> name value Set the Nix configuration option name to value. This overrides set- tings in the Nix configuration file (see nix.conf5). • --repair <#opt-repair> Fix corrupted or missing store paths by redownloading or rebuilding them. Note that this is slow because it requires computing a cryp- tographic hash of the contents of every path in the closure of the build. Also note the warning under nix-store --repair-path. Note See man nix.conf <../command-ref/conf-file.md#command-line-flags> for overriding configuration settings with command line flags. Common Environment Variables Most Nix commands interpret the following environment variables: • IN_NIX_SHELL <#env-IN_NIX_SHELL> Indicator that tells if the current environment was set up by nix- shell. It can have the values pure or impure. • NIX_PATH <#env-NIX_PATH> A colon-separated list of search path entries used to resolve lookup paths <../language/constructs/lookup-path.md>. This environment variable overrides the value of the nix-path con- figuration setting <../command-ref/conf-file.md#conf-nix-path>. It can be extended using the -I option <../command-ref/opt-com- mon.md#opt-I>. Example $ export NIX_PATH=`/home/eelco/Dev:nixos-config=/etc/nixos If NIX_PATH is set to an empty string, resolving search paths will always fail. Example $ NIX_PATH= nix-instantiate --eval '<nixpkgs>' error: file 'nixpkgs' was not found in the Nix search path (add it using $NIX_PATH or -I) • NIX_IGNORE_SYMLINK_STORE <#env-NIX_IGNORE_SYMLINK_STORE> Normally, the Nix store directory (typically /nix/store) is not al- lowed to contain any symlink components. This is to prevent impure builds. Builders sometimes canonicalise paths by resolving all sym- link components. Thus, builds on different machines (with /nix/store resolving to different locations) could yield different results. This is generally not a problem, except when builds are deployed to machines where /nix/store resolves differently. If you are sure that youre not going to do that, you can set NIX_IGNORE_SYMLINK_STORE to 1. Note that if youre symlinking the Nix store so that you can put it on another file system than the root file system, on Linux youre better off using bind mount points, e.g., $ mkdir /nix $ mount -o bind /mnt/otherdisk/nix /nix Consult the mount 8 manual page for details. • NIX_STORE_DIR <#env-NIX_STORE_DIR> Overrides the location of the Nix store (default prefix/store). • NIX_DATA_DIR <#env-NIX_DATA_DIR> Overrides the location of the Nix static data directory (default prefix/share). • NIX_LOG_DIR <#env-NIX_LOG_DIR> Overrides the location of the Nix log directory (default pre- fix/var/log/nix). • NIX_STATE_DIR <#env-NIX_STATE_DIR> Overrides the location of the Nix state directory (default pre- fix/var/nix). • NIX_CONF_DIR <#env-NIX_CONF_DIR> Overrides the location of the system Nix configuration directory (default sysconfdir/nix, i.e. /etc/nix on most systems). • NIX_CONFIG <#env-NIX_CONFIG> Applies settings from Nix configuration from the environment. The content is treated as if it was read from a Nix configuration file. Settings are separated by the newline character. • NIX_USER_CONF_FILES <#env-NIX_USER_CONF_FILES> Overrides the location of the Nix user configuration files to load from. The default are the locations according to the XDG Base Directory Specification <https://specifications.freedesktop.org/basedir- spec/basedir-spec-latest.html>. See the XDG Base Directories <#xdg- base-directories> sub-section for details. The variable is treated as a list separated by the : token. • TMPDIR <#env-TMPDIR> Use the specified directory to store temporary files. In particular, this includes temporary build directories; these can take up sub- stantial amounts of disk space. The default is /tmp. • NIX_REMOTE <#env-NIX_REMOTE> This variable should be set to daemon if you want to use the Nix daemon to execute Nix operations. This is necessary in multi-user Nix installations <../installation/multi-user.md>. If the Nix dae- mon's Unix socket is at some non-standard path, this variable should be set to unix://path/to/socket. Otherwise, it should be left unset. • NIX_SHOW_STATS <#env-NIX_SHOW_STATS> If set to 1, Nix will print some evaluation statistics, such as the number of values allocated. • NIX_COUNT_CALLS <#env-NIX_COUNT_CALLS> If set to 1, Nix will print how often functions were called during Nix expression evaluation. This is useful for profiling your Nix ex- pressions. • GC_INITIAL_HEAP_SIZE <#env-GC_INITIAL_HEAP_SIZE> If Nix has been configured to use the Boehm garbage collector, this variable sets the initial size of the heap in bytes. It defaults to 384 MiB. Setting it to a low value reduces memory consumption, but will increase runtime due to the overhead of garbage collection. XDG Base Directories Nix follows the XDG Base Directory Specification <https://specifica- tions.freedesktop.org/basedir-spec/basedir-spec-latest.html>. For backwards compatibility, Nix commands will follow the standard only when use-xdg-base-directories <../command-ref/conf-file.md#conf-use- xdg-base-directories> is enabled. New Nix commands <../command- ref/new-cli/nix.md> (experimental) conform to the standard by default. The following environment variables are used to determine locations of various state and configuration files: • [XDG_CONFIG_HOME]{#env-XDGCONFIGHOME} (default ~/.config) • [XDG_STATE_HOME]{#env-XDGSTATEHOME} (default ~/.local/state) • [XDG_CACHE_HOME]{#env-XDGCACHEHOME} (default ~/.cache) In addition, setting the following environment variables overrides the XDG base directories: • [NIX_CONFIG_HOME]{#env-NIXCONFIGHOME} (default $XDG_CONFIG_HOME/nix) • [NIX_STATE_HOME]{#env-NIXSTATEHOME} (default $XDG_STATE_HOME/nix) • [NIX_CACHE_HOME]{#env-NIXCACHEHOME} (default $XDG_CACHE_HOME/nix) When use-xdg-base-directories <../command-ref/conf-file.md#conf-use- xdg-base-directories> is enabled, the configuration directory is: 1. $NIX_CONFIG_HOME, if it is defined 2. Otherwise, $XDG_CONFIG_HOME/nix, if XDG_CONFIG_HOME is defined 3. Otherwise, ~/.config/nix. Likewise for the state and cache directories. Examples $ nix-build '<nixpkgs>' --attr firefox store derivation is /nix/store/qybprl8sz2lc...-firefox-1.5.0.7.drv /nix/store/d18hyl92g30l...-firefox-1.5.0.7 $ ls -l result lrwxrwxrwx ... result -> /nix/store/d18hyl92g30l...-firefox-1.5.0.7 $ ls ./result/bin/ firefox firefox-config If a derivation has multiple outputs, nix-build will build the default (first) output. You can also build all outputs: $ nix-build '<nixpkgs>' --attr openssl.all This will create a symlink for each output named result-outputname. The suffix is omitted if the output name is out. So if openssl has out- puts out, bin and man, nix-build will create symlinks result, result- bin and result-man. Its also possible to build a specific output: $ nix-build '<nixpkgs>' --attr openssl.man This will create a symlink result-man. Build a Nix expression given on the command line: $ nix-build --expr 'with import <nixpkgs> { }; runCommand "foo" { } "echo bar > $out"' $ cat ./result bar Build the GNU Hello package from the latest revision of the master branch of Nixpkgs: $ nix-build https://github.com/NixOS/nixpkgs/archive/master.tar.gz --attr hello nix-build(1)
Name | Synopsis | Disambiguation | Description | Options | Special exit codes for build failure | Common Options | Common Environment Variables | Examples
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