'\" t
.\" Title: nix-shell
.\" Author: Eelco Dolstra
.\" Generator: DocBook XSL Stylesheets v1.79.2
.\" Date: 12/12/2020
.\" Manual: Command Reference
.\" Source: Nix 2.3.7
.\" Language: English
.\"
.TH "NIX\-SHELL" "1" "12/12/2020" "Nix 2\&.3\&.7" "Command Reference"
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.SH "NAME"
nix-shell \- start an interactive shell based on a Nix expression
.SH "SYNOPSIS"
.HP \w'\fBnix\-shell\fR\ 'u
\fBnix\-shell\fR [\fB\-\-arg\fR\ \fIname\fR\ \fIvalue\fR] [\fB\-\-argstr\fR\ \fIname\fR\ \fIvalue\fR] [{\fB\-\-attr\fR\ |\ \fB\-A\fR}\ \fIattrPath\fR] [\fB\-\-command\fR\ \fIcmd\fR] [\fB\-\-run\fR\ \fIcmd\fR] [\fB\-\-exclude\fR\ \fIregexp\fR] [\fB\-\-pure\fR] [\fB\-\-keep\fR\ \fIname\fR] {{\fB\-\-packages\fR\ |\ \fB\-p\fR}\ \fIpackages\fR... | [\fIpath\fR]}
.SH "DESCRIPTION"
.PP
The command
\fBnix\-shell\fR
will build the dependencies of the specified derivation, but not the derivation itself\&. It will then start an interactive shell in which all environment variables defined by the derivation
\fIpath\fR
have been set to their corresponding values, and the script
$stdenv/setup
has been sourced\&. This is useful for reproducing the environment of a derivation for development\&.
.PP
If
\fIpath\fR
is not given,
\fBnix\-shell\fR
defaults to
shell\&.nix
if it exists, and
default\&.nix
otherwise\&.
.PP
If
\fIpath\fR
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\&.
.PP
If the derivation defines the variable
\fIshellHook\fR, it will be evaluated after
$stdenv/setup
has been sourced\&. Since this hook is not executed by regular Nix builds, it allows you to perform initialisation specific to
\fBnix\-shell\fR\&. For example, the derivation attribute
.sp
.if n \{\
.RS 4
.\}
.nf
shellHook =
\*(Aq\*(Aq
echo "Hello shell"
\*(Aq\*(Aq;
.fi
.if n \{\
.RE
.\}
.sp
will cause
\fBnix\-shell\fR
to print
Hello shell\&.
.SH "OPTIONS"
.PP
All options not listed here are passed to
\fBnix\-store \-\-realise\fR, except for
\fB\-\-arg\fR
and
\fB\-\-attr\fR
/
\fB\-A\fR
which are passed to
\fBnix\-instantiate\fR\&.
.PP
\fB\-\-command\fR \fIcmd\fR
.RS 4
In the environment of the derivation, run the shell command
\fIcmd\fR\&. This command is executed in an interactive shell\&. (Use
\fB\-\-run\fR
to use a non\-interactive shell instead\&.) However, a call to
exit
is implicitly added to the command, so the shell will exit after running the command\&. To prevent this, add
return
at the end; e\&.g\&.
\-\-command "echo Hello; return"
will print
Hello
and then drop you into the interactive shell\&. This can be useful for doing any additional initialisation\&.
.RE
.PP
\fB\-\-run\fR \fIcmd\fR
.RS 4
Like
\fB\-\-command\fR, but executes the command in a non\-interactive shell\&. This means (among other things) that if you hit Ctrl\-C while the command is running, the shell exits\&.
.RE
.PP
\fB\-\-exclude\fR \fIregexp\fR
.RS 4
Do not build any dependencies whose store path matches the regular expression
\fIregexp\fR\&. This option may be specified multiple times\&.
.RE
.PP
\fB\-\-pure\fR
.RS 4
If this flag is specified, the environment is almost entirely cleared before the interactive shell is started, so you get an environment that more closely corresponds to the \(lqreal\(rq Nix build\&. A few variables, in particular
\fBHOME\fR,
\fBUSER\fR
and
\fBDISPLAY\fR, are retained\&. Note that
~/\&.bashrc
and (depending on your Bash installation)
/etc/bashrc
are still sourced, so any variables set there will affect the interactive shell\&.
.RE
.PP
\fB\-\-packages\fR / \fB\-p\fR \fIpackages\fR\&...
.RS 4
Set up an environment in which the specified packages are present\&. The command line arguments are interpreted as attribute names inside the Nix Packages collection\&. Thus,
nix\-shell \-p libjpeg openjdk
will start a shell in which the packages denoted by the attribute names
\fIlibjpeg\fR
and
\fIopenjdk\fR
are present\&.
.RE
.PP
\fB\-i\fR \fIinterpreter\fR
.RS 4
The chained script interpreter to be invoked by
\fBnix\-shell\fR\&. Only applicable in
#!\-scripts (described
below)\&.
.RE
.PP
\fB\-\-keep\fR \fIname\fR
.RS 4
When a
\fB\-\-pure\fR
shell is started, keep the listed environment variables\&.
.RE
.PP
The following common options are supported:
.PP
\fB\-\-help\fR
.RS 4
Prints out a summary of the command syntax and exits\&.
.RE
.PP
\fB\-\-version\fR
.RS 4
Prints out the Nix version number on standard output and exits\&.
.RE
.PP
\fB\-\-verbose\fR / \fB\-v\fR
.RS 4
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\&.
.sp
This option may be specified repeatedly\&. Currently, the following verbosity levels exist:
.PP
0
.RS 4
\(lqErrors only\(rq: only print messages explaining why the Nix invocation failed\&.
.RE
.PP
1
.RS 4
\(lqInformational\(rq: print
\fIuseful\fR
messages about what Nix is doing\&. This is the default\&.
.RE
.PP
2
.RS 4
\(lqTalkative\(rq: print more informational messages\&.
.RE
.PP
3
.RS 4
\(lqChatty\(rq: print even more informational messages\&.
.RE
.PP
4
.RS 4
\(lqDebug\(rq: print debug information\&.
.RE
.PP
5
.RS 4
\(lqVomit\(rq: print vast amounts of debug information\&.
.RE
.RE
.PP
\fB\-\-quiet\fR
.RS 4
Decreases the level of verbosity of diagnostic messages printed on standard error\&. This is the inverse option to
\fB\-v\fR
/
\fB\-\-verbose\fR\&.
.sp
This option may be specified repeatedly\&. See the previous verbosity levels list\&.
.RE
.PP
\fB\-\-no\-build\-output\fR / \fB\-Q\fR
.RS 4
By default, output written by builders to standard output and standard error is echoed to the Nix command\*(Aqs standard error\&. This option suppresses this behaviour\&. Note that the builder\*(Aqs standard output and error are always written to a log file in
\fIprefix\fR/nix/var/log/nix\&.
.RE
.PP
\fB\-\-max\-jobs\fR / \fB\-j\fR \fInumber\fR
.RS 4
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\&.
.sp
Setting it to
0
disallows building on the local machine, which is useful when you want builds to happen only on remote builders\&.
.RE
.PP
\fB\-\-cores\fR
.RS 4
Sets the value of the
\fBNIX_BUILD_CORES\fR
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
\fIenableParallelBuilding\fR
is set to
true, the builder passes the
\fB\-j\fR\fB\fIN\fR\fR
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\&.
.RE
.PP
\fB\-\-max\-silent\-time\fR
.RS 4
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\&.
.RE
.PP
\fB\-\-timeout\fR
.RS 4
Sets the maximum number of seconds that a builder can run\&. The default is specified by the
timeout
configuration setting\&.
0
means no timeout\&.
.RE
.PP
\fB\-\-keep\-going\fR / \fB\-k\fR
.RS 4
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)\&.
.RE
.PP
\fB\-\-keep\-failed\fR / \fB\-K\fR
.RS 4
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\&.
.RE
.PP
\fB\-\-fallback\fR
.RS 4
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\&.
.sp
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)\&.
.RE
.PP
\fB\-\-no\-build\-hook\fR
.RS 4
Disables the build hook mechanism\&. This allows to ignore remote builders if they are setup on the machine\&.
.sp
It\*(Aqs 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\&.
.RE
.PP
\fB\-\-readonly\-mode\fR
.RS 4
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\&.
.RE
.PP
\fB\-\-arg\fR \fIname\fR \fIvalue\fR
.RS 4
This option is accepted by
\fBnix\-env\fR,
\fBnix\-instantiate\fR
and
\fBnix\-build\fR\&. 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\&.,
{ \fIargName\fR ? \fIdefaultValue\fR }: \fI\&.\&.\&.\fR)\&. With
\fB\-\-arg\fR, 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
\fIname\fR, it will call it with value
\fIvalue\fR\&.
.sp
For instance, the top\-level
default\&.nix
in Nixpkgs is actually a function:
.sp
.if n \{\
.RS 4
.\}
.nf
{ # The system (e\&.g\&., `i686\-linux\*(Aq) for which to build the packages\&.
system ? builtins\&.currentSystem
\fI\&.\&.\&.\fR
}: \fI\&.\&.\&.\fR
.fi
.if n \{\
.RE
.\}
.sp
So if you call this Nix expression (e\&.g\&., when you do
nix\-env \-i \fIpkgname\fR), the function will be called automatically using the value
builtins\&.currentSystem
for the
system
argument\&. You can override this using
\fB\-\-arg\fR, e\&.g\&.,
nix\-env \-i \fIpkgname\fR \-\-arg system \e"i686\-freebsd\e"\&. (Note that since the argument is a Nix string literal, you have to escape the quotes\&.)
.RE
.PP
\fB\-\-argstr\fR \fIname\fR \fIvalue\fR
.RS 4
This option is like
\fB\-\-arg\fR, only the value is not a Nix expression but a string\&. So instead of
\-\-arg system \e"i686\-linux\e"
(the outer quotes are to keep the shell happy) you can say
\-\-argstr system i686\-linux\&.
.RE
.PP
\fB\-\-attr\fR / \fB\-A\fR \fIattrPath\fR
.RS 4
Select an attribute from the top\-level Nix expression being evaluated\&. (\fBnix\-env\fR,
\fBnix\-instantiate\fR,
\fBnix\-build\fR
and
\fBnix\-shell\fR
only\&.) The
\fIattribute path\fR
\fIattrPath\fR
is a sequence of attribute names separated by dots\&. For instance, given a top\-level Nix expression
\fIe\fR, the attribute path
xorg\&.xorgserver
would cause the expression
\fIe\fR\&.xorg\&.xorgserver
to be used\&. See
\fBnix\-env \-\-install\fR
for some concrete examples\&.
.sp
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\&.
.RE
.PP
\fB\-\-expr\fR / \fB\-E\fR
.RS 4
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\&. (\fBnix\-instantiate\fR,
\fBnix\-build\fR
and
\fBnix\-shell\fR
only\&.)
.RE
.PP
\fB\-I\fR \fIpath\fR
.RS 4
Add a path to the Nix expression search path\&. This option may be given multiple times\&. See the
\fBNIX_PATH\fR
environment variable for information on the semantics of the Nix search path\&. Paths added through
\fB\-I\fR
take precedence over
\fBNIX_PATH\fR\&.
.RE
.PP
\fB\-\-option\fR \fIname\fR \fIvalue\fR
.RS 4
Set the Nix configuration option
\fIname\fR
to
\fIvalue\fR\&. This overrides settings in the Nix configuration file (see
\fBnix.conf\fR(5))\&.
.RE
.PP
\fB\-\-repair\fR
.RS 4
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
\fBnix\-store \-\-repair\-path\fR\&.
.RE
.SH "ENVIRONMENT VARIABLES"
.PP
\fBNIX_BUILD_SHELL\fR
.RS 4
Shell used to start the interactive environment\&. Defaults to the
\fBbash\fR
found in
\fBPATH\fR\&.
.RE
.SH "EXAMPLES"
.PP
To build the dependencies of the package Pan, and start an interactive shell in which to build it:
.sp
.if n \{\
.RS 4
.\}
.nf
$ nix\-shell \*(Aq\*(Aq \-A pan
[nix\-shell]$ unpackPhase
[nix\-shell]$ cd pan\-*
[nix\-shell]$ configurePhase
[nix\-shell]$ buildPhase
[nix\-shell]$ \&./pan/gui/pan
.fi
.if n \{\
.RE
.\}
.sp
To clear the environment first, and do some additional automatic initialisation of the interactive shell:
.sp
.if n \{\
.RS 4
.\}
.nf
$ nix\-shell \*(Aq\*(Aq \-A pan \-\-pure \e
\-\-command \*(Aqexport NIX_DEBUG=1; export NIX_CORES=8; return\*(Aq
.fi
.if n \{\
.RE
.\}
.sp
Nix expressions can also be given on the command line\&. For instance, the following starts a shell containing the packages
sqlite
and
libX11:
.sp
.if n \{\
.RS 4
.\}
.nf
$ nix\-shell \-E \*(Aqwith import { }; runCommand "dummy" { buildInputs = [ sqlite xorg\&.libX11 ]; } ""\*(Aq
.fi
.if n \{\
.RE
.\}
.sp
A shorter way to do the same is:
.sp
.if n \{\
.RS 4
.\}
.nf
$ nix\-shell \-p sqlite xorg\&.libX11
[nix\-shell]$ echo $NIX_LDFLAGS
\&... \-L/nix/store/j1zg5v\&...\-sqlite\-3\&.8\&.0\&.2/lib \-L/nix/store/0gmcz9\&...\-libX11\-1\&.6\&.1/lib \&...
.fi
.if n \{\
.RE
.\}
.sp
The
\fB\-p\fR
flag looks up Nixpkgs in the Nix search path\&. You can override it by passing
\fB\-I\fR
or setting
\fBNIX_PATH\fR\&. For example, the following gives you a shell containing the Pan package from a specific revision of Nixpkgs:
.sp
.if n \{\
.RS 4
.\}
.nf
$ nix\-shell \-p pan \-I nixpkgs=https://github\&.com/NixOS/nixpkgs\-channels/archive/8a3eea054838b55aca962c3fbde9c83c102b8bf2\&.tar\&.gz
[nix\-shell:~]$ pan \-\-version
Pan 0\&.139
.fi
.if n \{\
.RE
.\}
.sp
.SH "USE AS A #!\-INTERPRETER"
.PP
You can use
\fBnix\-shell\fR
as a script interpreter to allow scripts written in arbitrary languages to obtain their own dependencies via Nix\&. This is done by starting the script with the following lines:
.sp
.if n \{\
.RS 4
.\}
.nf
#! /usr/bin/env nix\-shell
#! nix\-shell \-i \fIreal\-interpreter\fR \-p \fIpackages\fR
.fi
.if n \{\
.RE
.\}
.sp
where
\fIreal\-interpreter\fR
is the \(lqreal\(rq script interpreter that will be invoked by
\fBnix\-shell\fR
after it has obtained the dependencies and initialised the environment, and
\fIpackages\fR
are the attribute names of the dependencies in Nixpkgs\&.
.PP
The lines starting with
#! nix\-shell
specify
\fBnix\-shell\fR
options (see above)\&. Note that you cannot write
#! /usr/bin/env nix\-shell \-i \&.\&.\&.
because many operating systems only allow one argument in
#!
lines\&.
.PP
For example, here is a Python script that depends on Python and the
prettytable
package:
.sp
.if n \{\
.RS 4
.\}
.nf
#! /usr/bin/env nix\-shell
#! nix\-shell \-i python \-p python pythonPackages\&.prettytable
import prettytable
# Print a simple table\&.
t = prettytable\&.PrettyTable(["N", "N^2"])
for n in range(1, 10): t\&.add_row([n, n * n])
print t
.fi
.if n \{\
.RE
.\}
.PP
Similarly, the following is a Perl script that specifies that it requires Perl and the
HTML::TokeParser::Simple
and
LWP
packages:
.sp
.if n \{\
.RS 4
.\}
.nf
#! /usr/bin/env nix\-shell
#! nix\-shell \-i perl \-p perl perlPackages\&.HTMLTokeParserSimple perlPackages\&.LWP
use HTML::TokeParser::Simple;
# Fetch nixos\&.org and print all hrefs\&.
my $p = HTML::TokeParser::Simple\->new(url => \*(Aqhttp://nixos\&.org/\*(Aq);
while (my $token = $p\->get_tag("a")) {
my $href = $token\->get_attr("href");
print "$href\en" if $href;
}
.fi
.if n \{\
.RE
.\}
.PP
Sometimes you need to pass a simple Nix expression to customize a package like Terraform:
.sp
.if n \{\
.RS 4
.\}
.nf
#! /usr/bin/env nix\-shell
#! nix\-shell \-i bash \-p "terraform\&.withPlugins (plugins: [ plugins\&.openstack ])"
terraform apply
.fi
.if n \{\
.RE
.\}
.sp
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBNote\fR
.ps -1
.br
.PP
You must use double quotes (") when passing a simple Nix expression in a nix\-shell shebang\&.
.sp .5v
.RE
.PP
Finally, using the merging of multiple nix\-shell shebangs the following Haskell script uses a specific branch of Nixpkgs/NixOS (the 18\&.03 stable branch):
.sp
.if n \{\
.RS 4
.\}
.nf
#! /usr/bin/env nix\-shell
#! nix\-shell \-i runghc \-p "haskellPackages\&.ghcWithPackages (ps: [ps\&.HTTP ps\&.tagsoup])"
#! nix\-shell \-I nixpkgs=https://github\&.com/NixOS/nixpkgs\-channels/archive/nixos\-18\&.03\&.tar\&.gz
import Network\&.HTTP
import Text\&.HTML\&.TagSoup
\-\- Fetch nixos\&.org and print all hrefs\&.
main = do
resp <\- Network\&.HTTP\&.simpleHTTP (getRequest "http://nixos\&.org/")
body <\- getResponseBody resp
let tags = filter (isTagOpenName "a") $ parseTags body
let tags\*(Aq = map (fromAttrib "href") tags
mapM_ putStrLn $ filter (/= "") tags\*(Aq
.fi
.if n \{\
.RE
.\}
.sp
If you want to be even more precise, you can specify a specific revision of Nixpkgs:
.sp
.if n \{\
.RS 4
.\}
.nf
#! nix\-shell \-I nixpkgs=https://github\&.com/NixOS/nixpkgs\-channels/archive/0672315759b3e15e2121365f067c1c8c56bb4722\&.tar\&.gz
.fi
.if n \{\
.RE
.\}
.PP
The examples above all used
\fB\-p\fR
to get dependencies from Nixpkgs\&. You can also use a Nix expression to build your own dependencies\&. For example, the Python example could have been written as:
.sp
.if n \{\
.RS 4
.\}
.nf
#! /usr/bin/env nix\-shell
#! nix\-shell deps\&.nix \-i python
.fi
.if n \{\
.RE
.\}
.sp
where the file
deps\&.nix
in the same directory as the
#!\-script contains:
.sp
.if n \{\
.RS 4
.\}
.nf
with import {};
runCommand "dummy" { buildInputs = [ python pythonPackages\&.prettytable ]; } ""
.fi
.if n \{\
.RE
.\}
.sp
.SH "ENVIRONMENT VARIABLES"
.PP
\fBIN_NIX_SHELL\fR
.RS 4
Indicator that tells if the current environment was set up by
\fBnix\-shell\fR\&. Since Nix 2\&.0 the values are
"pure"
and
"impure"
.RE
.PP
\fBNIX_PATH\fR
.RS 4
A colon\-separated list of directories used to look up Nix expressions enclosed in angle brackets (i\&.e\&.,
<\fIpath\fR>)\&. For instance, the value
.sp
.if n \{\
.RS 4
.\}
.nf
/home/eelco/Dev:/etc/nixos
.fi
.if n \{\
.RE
.\}
.sp
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
.sp
.if n \{\
.RS 4
.\}
.nf
nixpkgs=/home/eelco/Dev/nixpkgs\-branch:/etc/nixos
.fi
.if n \{\
.RE
.\}
.sp
will cause Nix to search for
in
/home/eelco/Dev/nixpkgs\-branch/\fIpath\fR
and
/etc/nixos/nixpkgs/\fIpath\fR\&.
.sp
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
\fBNIX_PATH\fR
to
.sp
.if n \{\
.RS 4
.\}
.nf
nixpkgs=https://github\&.com/NixOS/nixpkgs\-channels/archive/nixos\-15\&.09\&.tar\&.gz
.fi
.if n \{\
.RE
.\}
.sp
tells Nix to download the latest revision in the Nixpkgs/NixOS 15\&.09 channel\&.
.sp
A following shorthand can be used to refer to the official channels:
.sp
.if n \{\
.RS 4
.\}
.nf
nixpkgs=channel:nixos\-15\&.09
.fi
.if n \{\
.RE
.\}
.sp
The search path can be extended using the
\fB\-I\fR
option, which takes precedence over
\fBNIX_PATH\fR\&.
.RE
.PP
\fBNIX_IGNORE_SYMLINK_STORE\fR
.RS 4
Normally, the Nix store directory (typically
/nix/store) is not allowed to contain any symlink components\&. This is to prevent \(lqimpure\(rq builds\&. Builders sometimes \(lqcanonicalise\(rq 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\(cqre not going to do that, you can set
\fBNIX_IGNORE_SYMLINK_STORE\fR
to
\fB1\fR\&.
.sp
Note that if you\(cqre symlinking the Nix store so that you can put it on another file system than the root file system, on Linux you\(cqre better off using
bind
mount points, e\&.g\&.,
.sp
.if n \{\
.RS 4
.\}
.nf
$ mkdir /nix
$ mount \-o bind /mnt/otherdisk/nix /nix
.fi
.if n \{\
.RE
.\}
.sp
Consult the
\fBmount\fR(8)
manual page for details\&.
.RE
.PP
\fBNIX_STORE_DIR\fR
.RS 4
Overrides the location of the Nix store (default
\fIprefix\fR/store)\&.
.RE
.PP
\fBNIX_DATA_DIR\fR
.RS 4
Overrides the location of the Nix static data directory (default
\fIprefix\fR/share)\&.
.RE
.PP
\fBNIX_LOG_DIR\fR
.RS 4
Overrides the location of the Nix log directory (default
\fIprefix\fR/var/log/nix)\&.
.RE
.PP
\fBNIX_STATE_DIR\fR
.RS 4
Overrides the location of the Nix state directory (default
\fIprefix\fR/var/nix)\&.
.RE
.PP
\fBNIX_CONF_DIR\fR
.RS 4
Overrides the location of the Nix configuration directory (default
\fIprefix\fR/etc/nix)\&.
.RE
.PP
\fBTMPDIR\fR
.RS 4
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\&.
.RE
.PP
\fBNIX_REMOTE\fR
.RS 4
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\*(Aqs Unix socket is at some non\-standard path, this variable should be set to
unix://path/to/socket\&. Otherwise, it should be left unset\&.
.RE
.PP
\fBNIX_SHOW_STATS\fR
.RS 4
If set to
1, Nix will print some evaluation statistics, such as the number of values allocated\&.
.RE
.PP
\fBNIX_COUNT_CALLS\fR
.RS 4
If set to
1, Nix will print how often functions were called during Nix expression evaluation\&. This is useful for profiling your Nix expressions\&.
.RE
.PP
\fBGC_INITIAL_HEAP_SIZE\fR
.RS 4
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\&.
.RE
.SH "AUTHOR"
.PP
\fBEelco Dolstra\fR
.RS 4
Author
.RE
.SH "COPYRIGHT"
.br
Copyright \(co 2004-2018 Eelco Dolstra
.br