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nix-build(1) General Commands Manual nix-build(1)

Name
nix-build - build a Nix expression

Synopsis
nix-build [paths^a|] [--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 expres-
sions 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 multiple 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 cur-
rent directory, if it exists.

If an element of paths starts with http:// or https://, it is interpreted
as the URL of a tarball that will be downloaded and unpacked to a temporary
location. The tarball must include a single top-level directory containing
at least a file named default.nix.

nix-build is essentially a wrapper around nix-instantiate (to translate a
high-level Nix expression to a low-level store derivation) and nix-store
--realise (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 donat rename the symlink.

Options
All options not listed here are passed to nix-store --realise, except for
--arg and --attr / -A which are passed to nix-instantiate.

* --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

Show what store paths would be built or downloaded.

* --out-link / -o outlink

Change the name of the symlink to the output path created from result 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 specified
timeout.

* 102 Hash mismatch

The build output was rejected because it does not match the outputHash
attribute of the derivation.

* 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 occur.
In this case the 1xx status codes are or combined using bitwise OR.

0b1100100
^^^^
|||`- timeout
||`-- output hash mismatch
|`--- build failure
`---- not deterministic

Common Options
Most Nix commands accept the following command-line options:

* --help

Prints out a summary of the command syntax and exits.

* --version

Prints out the Nix version number on standard output and exits.

* --verbose / -v

Increases the level of verbosity of diagnostic messages printed on stan-
dard error. For each Nix operation, the information printed on standard
output is well-defined; any diagnostic information is printed on stan-
dard error, never on standard output.

This option may be specified repeatedly. Currently, the following ver-
bosity levels exist:

* 0 aErrors onlya

Only print messages explaining why the Nix invocation failed.

* 1 aInformationala

Print useful messages about what Nix is doing. This is the default.

* 2 aTalkativea

Print more informational messages.

* 3 aChattya

Print even more informational messages.

* 4 aDebuga

Print debug information.

* 5 aVomita

Print vast amounts of debug information.

* --quiet

Decreases the level of verbosity of diagnostic messages printed on stan-
dard error. This is the inverse option to -v / --verbose.

This option may be specified repeatedly. See the previous verbosity
levels list.

* --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 between re-
leases.
* 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 / -Q

By default, output written by builders to standard output and standard
error is echoed to the Nix command's standard error. This option sup-
presses this behaviour. Note that the builder's standard output and er-
ror are always written to a log file in prefix/nix/var/log/nix.

* --max-jobs / -j number

Sets the maximum number of build jobs that Nix will perform in parallel
to the specified number. Specify auto to use the number of CPUs in the
system. The default is specified by the max-jobs configuration 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

Sets the value of the NIX_BUILD_CORES environment variable in the invo-
cation of builders. Builders can use this variable at their discretion
to control the maximum amount of parallelism. For instance, in Nixpkgs,
if the derivation attribute enableParallelBuilding 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

Sets the maximum number of seconds that a builder can go without produc-
ing any data on standard output or standard error. The default is spec-
ified by the max-silent-time configuration setting. 0 means no time-
out.

* --timeout

Sets the maximum number of seconds that a builder can run. The default
is specified by the timeout configuration setting. 0 means no timeout.

* --keep-going / -k

Keep going in case of failed builds, to the greatest extent possible.
That is, if building an input of some derivation fails, Nix will still
build the other inputs, but not the derivation itself. Without this op-
tion, 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 / -K

Specifies that in case of a build failure, the temporary directory (usu-
ally in /tmp) in which the build takes place should not be deleted. The
path of the build directory is printed as an informational message.

* --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 regis-
tered substitutes in order to perform binary distribution from, say, a
network repository. If the repository is down, the realisation of the
derivation will fail. When this option is specified, Nix will build the
derivation instead. Thus, installation from binaries falls back on in-
stallation from source. This option is not the default since it is gen-
erally not desirable for a transient failure in obtaining the substi-
tutes to lead to a full build from source (with the related consumption
of resources).

* --readonly-mode

When this option is used, no attempt is made to open the Nix database.
Most Nix operations do need database access, so those operations will
fail.

* --arg name value

This option is accepted by nix-env, nix-instantiate, nix-shell and nix-
build. When evaluating Nix expressions, the expression evaluator will
automatically try to call functions that it encounters. It can automat-
ically call functions for which every argument has a default value
(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 func-
tion:

{ # 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 --in-
stall --attr pkgname), the function will be called automatically us-
ing the value builtins.currentSystem 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 argument
is a Nix string literal, you have to escape the quotes.)

* --arg-from-file name path

Pass the contents of file path as the argument name to Nix functions.

* --arg-from-stdin name

Pass the contents of stdin as the argument name to Nix functions.

* --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 / -A attrPath

Select an attribute from the top-level Nix expression being evaluated.
(nix-env, nix-instantiate, nix-build and nix-shell only.) The attribute
path attrPath is a sequence of attribute names separated 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 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 ex-
pression.

* --eval-store store-url

The URL to the Nix store to use for evaluation, i.e. where to store de-
rivations (.drv files) and inputs referenced by them.

* --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 expres-
sions. (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 path

Add an entry to the list of search paths used to resolve lookup paths.
This option may be given multiple times.

Paths added through -I take precedence over the nix-path configuration
setting and the NIX_PATH environment variable.

* --impure

Allow access to mutable paths and repositories.

* --option name value

Set the Nix configuration option name to value. This overrides settings
in the Nix configuration file (see nix.conf5).

* --repair

Fix corrupted or missing store paths by redownloading or rebuilding
them. Note that this is slow because it requires computing a crypto-
graphic 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 for overriding configuration settings with command line
flags.

Common Environment Variables
Most Nix commands interpret the following environment variables:

* 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

A colon-separated list of search path entries used to resolve lookup
paths.

This environment variable overrides the value of the nix-path configura-
tion setting.

It can be extended using the -I option.

Example

$ export NIX_PATH=`/home/eelco/Dev:nixos-config=/etc/nixos

If NIX_PATH is set to an empty string, resolving search paths will al-
ways 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

Normally, the Nix store directory (typically /nix/store) is not allowed
to contain any symlink components. This is to prevent aimpurea builds.
Builders sometimes acanonicalisea paths by resolving all symlink compo-
nents. 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 youare not going
to do that, you can set NIX_IGNORE_SYMLINK_STORE to 1.

Note that if youare symlinking the Nix store so that you can put it on
another file system than the root file system, on Linux youare 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

Overrides the location of the Nix store (default prefix/store).

* NIX_DATA_DIR

Overrides the location of the Nix static data directory (default pre-
fix/share).

* NIX_LOG_DIR

Overrides the location of the Nix log directory (default pre-
fix/var/log/nix).

* NIX_STATE_DIR

Overrides the location of the Nix state directory (default pre-
fix/var/nix).

* NIX_CONF_DIR

Overrides the location of the system Nix configuration directory (de-
fault sysconfdir/nix, i.e. /etc/nix on most systems).

* NIX_CONFIG

Applies settings from Nix configuration from the environment. The con-
tent is treated as if it was read from a Nix configuration file. Set-
tings are separated by the newline character.

* 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 Speci-
fication. See the XDG Base Directories sub-section for details.

The variable is treated as a list separated by the : token.

* TMPDIR

Use the specified directory to store temporary files. In particular,
this includes temporary build directories; these can take up substantial
amounts of disk space. The default is /tmp.

* 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 installa-
tions. If the Nix daemon'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

If set to 1, Nix will print some evaluation statistics, such as the num-
ber of values allocated.

* 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 expres-
sions.

* 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 in-
crease runtime due to the overhead of garbage collection.

XDG Base Directories
Nix follows the XDG Base Directory Specification.

For backwards compatibility, Nix commands will follow the standard only
when use-xdg-base-directories is enabled. New Nix commands (experimental)
conform to the standard by default.

The following environment variables are used to determine locations of var-
ious 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 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 outputs out,
bin and man, nix-build will create symlinks result, result-bin and result-
man. Itas 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)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=nix-build&sektion=1&manpath=FreeBSD+Ports+15.1.quarterly>

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