To explicitly select a single-user installation on your system:

  curl -L https://nixos.org/nix/install | sh -s -- --no-daemon

This will perform a single-user installation of Nix, meaning that /nix is owned by the invoking user. You should run this under your usual user account, not as root. The script will invoke sudo to create /nix if it doesn’t already exist. If you don’t have sudo, you should manually create /nix first as root, e.g.:

$ mkdir /nix
$ chown alice /nix

The install script will modify the first writable file from amongst .bash_profile, .bash_login and .profile to source ~/.nix-profile/etc/profile.d/nix.sh. You can set the NIX_INSTALLER_NO_MODIFY_PROFILE environment variable before executing the install script to disable this behaviour.

You can uninstall Nix simply by running:

$ rm -rf /nix

The multi-user Nix installation creates system users, and a system service for the Nix daemon.

You can instruct the installer to perform a multi-user installation on your system:

curl -L https://nixos.org/nix/install | sh -s -- --daemon

The multi-user installation of Nix will create build users between the user IDs 30001 and 30032, and a group with the group ID 30000. You should run this under your usual user account, not as root. The script will invoke sudo as needed.

The installer will modify /etc/bashrc, and /etc/zshrc if they exist. The installer will first back up these files with a .backup-before-nix extension. The installer will also create /etc/profile.d/nix.sh.

You can uninstall Nix with the following commands:

sudo rm -rf /etc/profile/nix.sh /etc/nix /nix ~root/.nix-profile ~root/.nix-defexpr ~root/.nix-channels ~/.nix-profile ~/.nix-defexpr ~/.nix-channels

# If you are on Linux with systemd, you will need to run:
sudo systemctl stop nix-daemon.socket
sudo systemctl stop nix-daemon.service
sudo systemctl disable nix-daemon.socket
sudo systemctl disable nix-daemon.service
sudo systemctl daemon-reload

# If you are on macOS, you will need to run:
sudo launchctl unload /Library/LaunchDaemons/org.nixos.nix-daemon.plist
sudo rm /Library/LaunchDaemons/org.nixos.nix-daemon.plist

There may also be references to Nix in /etc/profile, /etc/bashrc, and /etc/zshrc which you may remove.

Starting with macOS 10.15 (Catalina), the root filesystem is read-only. This means /nix can no longer live on your system volume, and that you'll need a workaround to install Nix.

The recommended approach, which creates an unencrypted APFS volume for your Nix store and a "synthetic" empty directory to mount it over at /nix, is least likely to impair Nix or your system.

If you're using a recent Mac with a T2 chip, your drive will still be encrypted at rest (in which case "unencrypted" is a bit of a misnomer). To use this approach, just install Nix with:

$ curl -L https://nixos.org/nix/install | sh -s -- --darwin-use-unencrypted-nix-store-volume

If you don't like the sound of this, you'll want to weigh the other approaches and tradeoffs detailed in this section.

alice$ diskutil apfs enableFileVault /nix -user disk

NixOS.org hosts version-specific installation URLs for all Nix versions since 1.11.16, at https://releases.nixos.org/nix/nix-version/install.

These install scripts can be used the same as the main NixOS.org installation script:

  curl -L https://nixos.org/nix/install | sh -s

In the same directory of the install script are sha256 sums, and gpg signature files.

You can also download a binary tarball that contains Nix and all its dependencies. (This is what the install script at https://nixos.org/nix/install does automatically.) You should unpack it somewhere (e.g. in /tmp), and then run the script named install inside the binary tarball:

alice$ cd /tmp
alice$ tar xfj nix-1.8-x86_64-darwin.tar.bz2
alice$ cd nix-1.8-x86_64-darwin
alice$ ./install

If you need to edit the multi-user installation script to use different group ID or a different user ID range, modify the variables set in the file named install-multi-user.

The source tarball of the most recent stable release can be downloaded from the Nix homepage. You can also grab the most recent development release.

Alternatively, the most recent sources of Nix can be obtained from its Git repository. For example, the following command will check out the latest revision into a directory called nix:

$ git clone https://github.com/NixOS/nix

Likewise, specific releases can be obtained from the tags of the repository.

After unpacking or checking out the Nix sources, issue the following commands:

$ ./configure options...
$ make
$ make install

Nix requires GNU Make so you may need to invoke gmake instead.

When building from the Git repository, these should be preceded by the command:

$ ./bootstrap.sh

The installation path can be specified by passing the --prefix=prefix to configure. The default installation directory is /usr/local. You can change this to any location you like. You must have write permission to the prefix path.

Nix keeps its store (the place where packages are stored) in /nix/store by default. This can be changed using --with-store-dir=path.

Nix keeps state (such as its database and log files) in /nix/var by default. This can be changed using --localstatedir=path.

In single-user mode, all Nix operations that access the database in prefix/var/nix/db or modify the Nix store in prefix/store must be performed under the user ID that owns those directories. This is typically root. (If you install from RPM packages, that’s in fact the default ownership.) However, on single-user machines, it is often convenient to chown those directories to your normal user account so that you don’t have to su to root all the time.

To allow a Nix store to be shared safely among multiple users, it is important that users are not able to run builders that modify the Nix store or database in arbitrary ways, or that interfere with builds started by other users. If they could do so, they could install a Trojan horse in some package and compromise the accounts of other users.

To prevent this, the Nix store and database are owned by some privileged user (usually root) and builders are executed under special user accounts (usually named nixbld1, nixbld2, etc.). When a unprivileged user runs a Nix command, actions that operate on the Nix store (such as builds) are forwarded to a Nix daemon running under the owner of the Nix store/database that performs the operation.

$ groupadd -r nixbld
$ for n in $(seq 1 10); do useradd -c "Nix build user $n" \
    -d /var/empty -g nixbld -G nixbld -M -N -r -s "$(which nologin)" \
    nixbld$n; done

$ nix-daemon

export NIX_REMOTE=daemon

$ chgrp nix-users /nix/var/nix/daemon-socket
$ chmod ug=rwx,o= /nix/var/nix/daemon-socket

If you need to specify a custom certificate bundle to account for an HTTPS-intercepting man in the middle proxy, you must specify the path to the certificate bundle in the environment variable NIX_SSL_CERT_FILE.

If you don't specify a NIX_SSL_CERT_FILE manually, Nix will install and use its own certificate bundle.

$ sudo launchctl setenv NIX_SSL_CERT_FILE /etc/ssl/my-certificate-bundle.crt
$ sudo launchctl kickstart -k system/org.nixos.nix-daemon

The roots of the garbage collector are all store paths to which there are symlinks in the directory prefix/nix/var/nix/gcroots. For instance, the following command makes the path /nix/store/d718ef...-foo a root of the collector:

$ ln -s /nix/store/d718ef...-foo /nix/var/nix/gcroots/bar

That is, after this command, the garbage collector will not remove /nix/store/d718ef...-foo or any of its dependencies.

Subdirectories of prefix/nix/var/nix/gcroots are also searched for symlinks. Symlinks to non-store paths are followed and searched for roots, but symlinks to non-store paths inside the paths reached in that way are not followed to prevent infinite recursion.

You can easily share the Nix store of a machine via HTTP. This allows other machines to fetch store paths from that machine to speed up installations. It uses the same binary cache mechanism that Nix usually uses to fetch pre-built binaries from https://cache.nixos.org.

The daemon that handles binary cache requests via HTTP, nix-serve, is not part of the Nix distribution, but you can install it from Nixpkgs:

$ nix-env -i nix-serve

You can then start the server, listening for HTTP connections on whatever port you like:

$ nix-serve -p 8080

To check whether it works, try the following on the client:

$ curl http://avalon:8080/nix-cache-info

which should print something like:

StoreDir: /nix/store
WantMassQuery: 1
Priority: 30

On the client side, you can tell Nix to use your binary cache using --option extra-binary-caches, e.g.:

$ nix-env -i firefox --option extra-binary-caches http://avalon:8080/

The option extra-binary-caches tells Nix to use this binary cache in addition to your default caches, such as https://cache.nixos.org. Thus, for any path in the closure of Firefox, Nix will first check if the path is available on the server avalon or another binary caches. If not, it will fall back to building from source.

You can also tell Nix to always use your binary cache by adding a line to the nix.conf configuration file like this:

binary-caches = http://avalon:8080/ https://cache.nixos.org/

The command nix-copy-closure copies a Nix store path along with all its dependencies to or from another machine via the SSH protocol. It doesn’t copy store paths that are already present on the target machine. For example, the following command copies Firefox with all its dependencies:

$ nix-copy-closure --to alice@itchy.example.org $(type -p firefox)

See nix-copy-closure(1) for details.

With nix-store --export and nix-store --import you can write the closure of a store path (that is, the path and all its dependencies) to a file, and then unpack that file into another Nix store. For example,

$ nix-store --export $(nix-store -qR $(type -p firefox)) > firefox.closure

writes the closure of Firefox to a file. You can then copy this file to another machine and install the closure:

$ nix-store --import < firefox.closure

Any store paths in the closure that are already present in the target store are ignored. It is also possible to pipe the export into another command, e.g. to copy and install a closure directly to/on another machine:

$ nix-store --export $(nix-store -qR $(type -p firefox)) | bzip2 | \
    ssh alice@itchy.example.org "bunzip2 | nix-store --import"

However, nix-copy-closure is generally more efficient because it only copies paths that are not already present in the target Nix store.

You can tell Nix to automatically fetch needed binaries from a remote Nix store via SSH. For example, the following installs Firefox, automatically fetching any store paths in Firefox’s closure if they are available on the server avalon:

$ nix-env -i firefox --substituters ssh://alice@avalon

This works similar to the binary cache substituter that Nix usually uses, only using SSH instead of HTTP: if a store path P is needed, Nix will first check if it’s available in the Nix store on avalon. If not, it will fall back to using the binary cache substituter, and then to building from source.

You can also copy the closure of some store path, without installing it into your profile, e.g.

$ nix-store -r /nix/store/m85bxg…-firefox-34.0.5 --substituters ssh://alice@avalon

This is essentially equivalent to doing

$ nix-copy-closure --from alice@avalon /nix/store/m85bxg…-firefox-34.0.5

You can use SSH’s forced command feature to set up a restricted user account for SSH substituter access, allowing read-only access to the local Nix store, but nothing more. For example, add the following lines to sshd_config to restrict the user nix-ssh:

Match User nix-ssh
  AllowAgentForwarding no
  AllowTcpForwarding no
  PermitTTY no
  PermitTunnel no
  X11Forwarding no
  ForceCommand nix-store --serve
Match All

On NixOS, you can accomplish the same by adding the following to your configuration.nix:

nix.sshServe.enable = true;
nix.sshServe.keys = [ "ssh-dss AAAAB3NzaC1k... bob@example.org" ];

where the latter line lists the public keys of users that are allowed to connect.

Nix has built-in support for storing and fetching store paths from Amazon S3 and S3 compatible services. This uses the same binary cache mechanism that Nix usually uses to fetch prebuilt binaries from cache.nixos.org.

The following options can be specified as URL parameters to the S3 URL:

In this example we will use the bucket named example-nix-cache.

{
    "Id": "DirectReads",
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowDirectReads",
            "Action": [
                "s3:GetObject",
                "s3:GetBucketLocation"
            ],
            "Effect": "Allow",
            "Resource": [
                "arn:aws:s3:::example-nix-cache",
                "arn:aws:s3:::example-nix-cache/*"
            ],
            "Principal": "*"
        }
    ]
}

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "UploadToCache",
      "Effect": "Allow",
      "Action": [
        "s3:AbortMultipartUpload",
        "s3:GetBucketLocation",
        "s3:GetObject",
        "s3:ListBucket",
        "s3:ListBucketMultipartUploads",
        "s3:ListMultipartUploadParts",
        "s3:PutObject"
      ],
      "Resource": [
        "arn:aws:s3:::example-nix-cache",
        "arn:aws:s3:::example-nix-cache/*"
      ]
    }
  ]
}

{ stdenv, fetchurl, perl }: 

stdenv.mkDerivation { 
  name = "hello-2.1.1"; 
  builder = ./builder.sh; 
  src = fetchurl { 
    url = ftp://ftp.nluug.nl/pub/gnu/hello/hello-2.1.1.tar.gz;
    sha256 = "1md7jsfd8pa45z73bz1kszpp01yw6x5ljkjk2hx7wl800any6465";
  };
  inherit perl; 
}

Example 14.1, “Nix expression for GNU Hello (default.nix)” shows a Nix expression for GNU Hello. It's actually already in the Nix Packages collection in pkgs/applications/misc/hello/ex-1/default.nix. It is customary to place each package in a separate directory and call the single Nix expression in that directory default.nix. The file has the following elements (referenced from the figure by number):

perl = perl;

source $stdenv/setup 

PATH=$perl/bin:$PATH 

tar xvfz $src 
cd hello-*
./configure --prefix=$out 
make 
make install

Example 14.2, “Build script for GNU Hello (builder.sh)” shows the builder referenced from Hello's Nix expression (stored in pkgs/applications/misc/hello/ex-1/builder.sh). The builder can actually be made a lot shorter by using the generic builder functions provided by stdenv, but here we write out the build steps to elucidate what a builder does. It performs the following steps:

If you are wondering about the absence of error checking on the result of various commands called in the builder: this is because the shell script is evaluated with Bash's -e option, which causes the script to be aborted if any command fails without an error check.

...

rec { 

  hello = import ../applications/misc/hello/ex-1  { 
    inherit fetchurl stdenv perl;
  };

  perl = import ../development/interpreters/perl { 
    inherit fetchurl stdenv;
  };

  fetchurl = import ../build-support/fetchurl {
    inherit stdenv; ...
  };

  stdenv = ...;

}

The Nix expression in Example 14.1, “Nix expression for GNU Hello (default.nix)” is a function; it is missing some arguments that have to be filled in somewhere. In the Nix Packages collection this is done in the file pkgs/top-level/all-packages.nix, where all Nix expressions for packages are imported and called with the appropriate arguments. Example 14.3, “Composing GNU Hello (all-packages.nix)” shows some fragments of all-packages.nix.

hello = callPackage ../applications/misc/hello/ex-1 { };

hello = callPackage ../applications/misc/hello/ex-1 { stdenv = myStdenv; };

You can now try to build Hello. Of course, you could do nix-env -i hello, but you may not want to install a possibly broken package just yet. The best way to test the package is by using the command nix-build, which builds a Nix expression and creates a symlink named result in the current directory:

$ nix-build -A hello
building path `/nix/store/632d2b22514d...-hello-2.1.1'
hello-2.1.1/
hello-2.1.1/intl/
hello-2.1.1/intl/ChangeLog
...

$ ls -l result
lrwxrwxrwx ... 2006-09-29 10:43 result -> /nix/store/632d2b22514d...-hello-2.1.1

$ ./result/bin/hello
Hello, world!

The -A option selects the hello attribute. This is faster than using the symbolic package name specified by the name attribute (which also happens to be hello) and is unambiguous (there can be multiple packages with the symbolic name hello, but there can be only one attribute in a set named hello).

nix-build registers the ./result symlink as a garbage collection root, so unless and until you delete the ./result symlink, the output of the build will be safely kept on your system. You can use nix-build’s -o switch to give the symlink another name.

Nix has transactional semantics. Once a build finishes successfully, Nix makes a note of this in its database: it registers that the path denoted by out is now “valid”. If you try to build the derivation again, Nix will see that the path is already valid and finish immediately. If a build fails, either because it returns a non-zero exit code, because Nix or the builder are killed, or because the machine crashes, then the output paths will not be registered as valid. If you try to build the derivation again, Nix will remove the output paths if they exist (e.g., because the builder died half-way through make install) and try again. Note that there is no “negative caching”: Nix doesn't remember that a build failed, and so a failed build can always be repeated. This is because Nix cannot distinguish between permanent failures (e.g., a compiler error due to a syntax error in the source) and transient failures (e.g., a disk full condition).

Nix also performs locking. If you run multiple Nix builds simultaneously, and they try to build the same derivation, the first Nix instance that gets there will perform the build, while the others block (or perform other derivations if available) until the build finishes:

$ nix-build -A hello
waiting for lock on `/nix/store/0h5b7hp8d4hqfrw8igvx97x1xawrjnac-hello-2.1.1x'

So it is always safe to run multiple instances of Nix in parallel (which isn’t the case with, say, make).

If you have a system with multiple CPUs, you may want to have Nix build different derivations in parallel (insofar as possible). Just pass the option -j N, where N is the maximum number of jobs to be run in parallel, or set. Typically this should be the number of CPUs.

Recall from Example 14.2, “Build script for GNU Hello (builder.sh)” that the builder looked something like this:

PATH=$perl/bin:$PATH
tar xvfz $src
cd hello-*
./configure --prefix=$out
make
make install

The builders for almost all Unix packages look like this — set up some environment variables, unpack the sources, configure, build, and install. For this reason the standard environment provides some Bash functions that automate the build process. A builder using the generic build facilities in shown in Example 14.4, “Build script using the generic build functions”.

buildInputs="$perl" 

source $stdenv/setup 

genericBuild 

Discerning readers will note that the buildInputs could just as well have been set in the Nix expression, like this:

  buildInputs = [ perl ];

The perl attribute can then be removed, and the builder becomes even shorter:

source $stdenv/setup
genericBuild

In fact, mkDerivation provides a default builder that looks exactly like that, so it is actually possible to omit the builder for Hello entirely.

Table 15.1, “Operators” lists the operators in the Nix expression language, in order of precedence (from strongest to weakest binding).

The most important built-in function is derivation, which is used to describe a single derivation (a build action). It takes as input a set, the attributes of which specify the inputs of the build.

The function mkDerivation in the Nixpkgs standard environment is a wrapper around derivation that adds a default value for system and always uses Bash as the builder, to which the supplied builder is passed as a command-line argument. See the Nixpkgs manual for details.

The builder is executed as follows:

This section lists the functions and constants built into the Nix expression evaluator. (The built-in function derivation is discussed above.) Some built-ins, such as derivation, are always in scope of every Nix expression; you can just access them right away. But to prevent polluting the namespace too much, most built-ins are not in scope. Instead, you can access them through the builtins built-in value, which is a set that contains all built-in functions and values. For instance, derivation is also available as builtins.derivation.

Verify a path which already exists in the Nix store by passing --check to the build command.

If the build passes and is deterministic, Nix will exit with a status code of 0:

$ nix-build ./deterministic.nix -A stable
these derivations will be built:
  /nix/store/z98fasz2jqy9gs0xbvdj939p27jwda38-stable.drv
building '/nix/store/z98fasz2jqy9gs0xbvdj939p27jwda38-stable.drv'...
/nix/store/yyxlzw3vqaas7wfp04g0b1xg51f2czgq-stable

$ nix-build ./deterministic.nix -A stable --check
checking outputs of '/nix/store/z98fasz2jqy9gs0xbvdj939p27jwda38-stable.drv'...
/nix/store/yyxlzw3vqaas7wfp04g0b1xg51f2czgq-stable

If the build is not deterministic, Nix will exit with a status code of 1:

$ nix-build ./deterministic.nix -A unstable
these derivations will be built:
  /nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv
building '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv'...
/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable

$ nix-build ./deterministic.nix -A unstable --check
checking outputs of '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv'...
error: derivation '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv' may not be deterministic: output '/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable' differs

In the Nix daemon's log, we will now see:

For derivation /nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv:
1c1
< 8108
---
> 30204

Using --check with --keep-failed will cause Nix to keep the second build's output in a special, .check path:

$ nix-build ./deterministic.nix -A unstable --check --keep-failed
checking outputs of '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv'...
note: keeping build directory '/tmp/nix-build-unstable.drv-0'
error: derivation '/nix/store/cgl13lbj1w368r5z8gywipl1ifli7dhk-unstable.drv' may not be deterministic: output '/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable' differs from '/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable.check'

In particular, notice the /nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable.check output. Nix has copied the build results to that directory where you can examine it.

--check is only usable if the derivation has been built on the system already. If the derivation has not been built Nix will fail with the error:

error: some outputs of '/nix/store/hzi1h60z2qf0nb85iwnpvrai3j2w7rr6-unstable.drv' are not valid, so checking is not possible

Run the build without --check, and then try with --check again.

Automatically verify every build at build time by executing the build multiple times.

Setting repeat and enforce-determinism in your nix.conf permits the automated verification of every build Nix performs.

The following configuration will run each build three times, and will require the build to be deterministic:

enforce-determinism = true
repeat = 2

Setting enforce-determinism to false as in the following configuration will run the build multiple times, execute the build hook, but will allow the build to succeed even if it does not build reproducibly:

enforce-determinism = false
repeat = 1

An example output of this configuration:

$ nix-build ./test.nix -A unstable
these derivations will be built:
  /nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv
building '/nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv' (round 1/2)...
building '/nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv' (round 2/2)...
output '/nix/store/6xg356v9gl03hpbbg8gws77n19qanh02-unstable' of '/nix/store/ch6llwpr2h8c3jmnf3f2ghkhx59aa97f-unstable.drv' differs from '/nix/store/6xg356v9gl03hpbbg8gws77n19qanh02-unstable.check' from previous round
/nix/store/6xg356v9gl03hpbbg8gws77n19qanh02-unstable

Here we use the post-build hook to upload to a binary cache. This is a simple and working example, but it is not suitable for all use cases.

The post build hook program runs after each executed build, and blocks the build loop. The build loop exits if the hook program fails.

Concretely, this implementation will make Nix slow or unusable when the internet is slow or unreliable.

A more advanced implementation might pass the store paths to a user-supplied daemon or queue for processing the store paths outside of the build loop.

This tutorial assumes you have configured an S3-compatible binary cache according to the instructions at Section 13.4.3, “Authenticated Writes to your S3-compatible binary cache”, and that the root user's default AWS profile can upload to the bucket.

Use nix-store --generate-binary-cache-key to create our public and private signing keys. We will sign paths with the private key, and distribute the public key for verifying the authenticity of the paths.

# nix-store --generate-binary-cache-key example-nix-cache-1 /etc/nix/key.private /etc/nix/key.public
# cat /etc/nix/key.public
example-nix-cache-1:1/cKDz3QCCOmwcztD2eV6Coggp6rqc9DGjWv7C0G+rM=

Then, add the public key and the cache URL to your nix.conf's trusted-public-keys and substituters like:

substituters = https://cache.nixos.org/ s3://example-nix-cache
trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= example-nix-cache-1:1/cKDz3QCCOmwcztD2eV6Coggp6rqc9DGjWv7C0G+rM=

we will restart the Nix daemon a later step.

Write the following script to /etc/nix/upload-to-cache.sh:

#!/bin/sh

set -eu
set -f # disable globbing
export IFS=' '

echo "Signing paths" $OUT_PATHS
nix sign-paths --key-file /etc/nix/key.private $OUT_PATHS
echo "Uploading paths" $OUT_PATHS
exec nix copy --to 's3://example-nix-cache' $OUT_PATHS

Then make sure the hook program is executable by the root user:

# chmod +x /etc/nix/upload-to-cache.sh

Edit /etc/nix/nix.conf to run our hook, by adding the following configuration snippet at the end:

post-build-hook = /etc/nix/upload-to-cache.sh

Then, restart the nix-daemon.

Build any derivation, for example:

$ nix-build -E '(import <nixpkgs> {}).writeText "example" (builtins.toString builtins.currentTime)'
these derivations will be built:
  /nix/store/s4pnfbkalzy5qz57qs6yybna8wylkig6-example.drv
building '/nix/store/s4pnfbkalzy5qz57qs6yybna8wylkig6-example.drv'...
running post-build-hook '/home/grahamc/projects/github.com/NixOS/nix/post-hook.sh'...
post-build-hook: Signing paths /nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example
post-build-hook: Uploading paths /nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example
/nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example

Then delete the path from the store, and try substituting it from the binary cache:

$ rm ./result
$ nix-store --delete /nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example

Now, copy the path back from the cache:

$ nix store --realize /nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example
copying path '/nix/store/m8bmqwrch6l3h8s0k3d673xpmipcdpsa-example from 's3://example-nix-cache'...
warning: you did not specify '--add-root'; the result might be removed by the garbage collector
/nix/store/m8bmqwrch6l3h8s0k3d673xpmipcdpsa-example

We now have a Nix installation configured to automatically sign and upload every local build to a remote binary cache.

Before deploying this to production, be sure to consider the implementation caveats in Section 19.1, “Implementation Caveats”.