OPTIONS¶
--add-root path, --indirect
See the corresponding options in nix-store.
--parse
Just parse the input files, and print their abstract
syntax trees on standard output in ATerm format.
--eval
Just parse and evaluate the input files, and print the
resulting values on standard output. No instantiation of store derivations
takes place.
--find-file
Look up the given files in Nix’s search path (as
specified by the NIX_PATH environment variable). If found, print the
corresponding absolute paths on standard output. For instance, if
NIX_PATH is nixpkgs=/home/alice/nixpkgs, then nix-instantiate
--find-file nixpkgs/default.nix will print
/home/alice/nixpkgs/default.nix.
--strict
When used with
--eval, recursively evaluate list
elements and attributes. Normally, such sub-expressions are left unevaluated
(since the Nix expression language is lazy).
Warning
This option can cause non-termination, because lazy data structures can be
infinitely large.
--json
When used with --eval, print the resulting value
as an JSON representation of the abstract syntax tree rather than as an
ATerm.
--xml
When used with --eval, print the resulting value
as an XML representation of the abstract syntax tree rather than as an ATerm.
The schema is the same as that used by the toXML built-in.
--read-write-mode
When used with --eval, perform evaluation in
read/write mode so nix language features that require it will still work (at
the cost of needing to do instantiation of every evaluated derivation). If
this option is not enabled, there may be uninstantiated store paths in the
final output.
--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 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
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.
--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
suppresses this behaviour. Note that the builder's standard output and error
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 invocation 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 producing any data on standard output or standard error. The default
is specified 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
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 / -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 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
registered 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
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).
--no-build-hook
Disables the build hook mechanism. This allows to ignore
remote builders if they are setup on the machine.
It's useful in cases where the bandwidth between the client and
the remote builder is too low. In that case it can take more time to upload
the sources to the remote builder and fetch back the result than to do the
computation locally.
--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 and
nix-build. When evaluating Nix expressions,
the expression evaluator will automatically try to call functions that it
encounters. It can automatically 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
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 -i
pkgname), the function will be called automatically using the value
builtins.currentSystem for the system argument. You can override this using
--arg, e.g., nix-env -i pkgname --arg system
\"i686-freebsd\". (Note that since the argument is a Nix string
literal, you have to escape the quotes.)
--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 expression.
--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.)
-I path
Add a path to the Nix expression search path. This option
may be given multiple times. See the NIX_PATH environment variable for
information on the semantics of the Nix search path. Paths added through
-I take precedence over NIX_PATH.
--option name value
Set the Nix configuration option
name to
value. This overrides settings in the Nix configuration file (see
nix.conf(5)).
--repair
Fix corrupted or missing store paths by redownloading or
rebuilding them. Note that this is slow because it requires computing a
cryptographic hash of the contents of every path in the closure of the build.
Also note the warning under nix-store --repair-path.
ENVIRONMENT VARIABLES¶
IN_NIX_SHELL
Indicator that tells if the current environment was set
up by nix-shell. Since Nix 2.0 the values are "pure" and
"impure"
NIX_PATH
A colon-separated list of directories used to look up Nix
expressions enclosed in angle brackets (i.e., <
path>). For
instance, the value
/home/eelco/Dev:/etc/nixos
will cause Nix to look for paths relative to /home/eelco/Dev and
/etc/nixos, in that order. It is also possible to match paths against a
prefix. For example, the value
nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos
will cause Nix to search for <nixpkgs/path> in
/home/eelco/Dev/nixpkgs-branch/path and
/etc/nixos/nixpkgs/path.
If a path in the Nix search path 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 consist of a single
top-level directory. For example, setting NIX_PATH to
tells Nix to download the latest revision in the Nixpkgs/NixOS
15.09 channel.
A following shorthand can be used to refer to the official
channels:
nixpkgs=channel:nixos-15.09
The search path can be extended using the -I option, which
takes precedence over NIX_PATH.
NIX_IGNORE_SYMLINK_STORE
Normally, the Nix store directory (typically /nix/store)
is not allowed to contain any symlink components. This is to prevent
“impure” builds. Builders sometimes “canonicalise”
paths by resolving all symlink 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
you’re not going to do that, you can set
NIX_IGNORE_SYMLINK_STORE to
1.
Note that if you’re symlinking the Nix store so that you
can put it on another file system than the root file system, on Linux
you’re 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 prefix/share).
NIX_LOG_DIR
Overrides the location of the Nix log directory (default
prefix/var/log/nix).
NIX_STATE_DIR
Overrides the location of the Nix state directory
(default prefix/var/nix).
NIX_CONF_DIR
Overrides the location of the Nix configuration directory
(default prefix/etc/nix).
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
installations. 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 number 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
expressions.
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.
