Name
nix.conf
- Nix configuration file
Description
Nix supports a variety of configuration settings, which are read from configuration files or taken as command line flags.
Configuration file
By default Nix reads settings from the following places, in that order:
-
The system-wide configuration file
sysconfdir/nix/nix.conf
(i.e./etc/nix/nix.conf
on most systems), or$NIX_CONF_DIR/nix.conf
ifNIX_CONF_DIR
is set.Values loaded in this file are not forwarded to the Nix daemon. The client assumes that the daemon has already loaded them.
-
If
NIX_USER_CONF_FILES
is set, then each path separated by:
will be loaded in reverse order.Otherwise it will look for
nix/nix.conf
files inXDG_CONFIG_DIRS
andXDG_CONFIG_HOME
. If unset,XDG_CONFIG_DIRS
defaults to/etc/xdg
, andXDG_CONFIG_HOME
defaults to$HOME/.config
as per XDG Base Directory Specification. -
If
NIX_CONFIG
is set, its contents are treated as the contents of a configuration file.
File format
Configuration files consist of name = value
pairs, one per line.
Comments start with a #
character.
Example:
keep-outputs = true # Nice for developers
keep-derivations = true # Idem
Other files can be included with a line like include <path>
, where <path>
is interpreted relative to the current configuration file.
A missing file is an error unless !include
is used instead.
A configuration setting usually overrides any previous value.
However, for settings that take a list of items, you can prefix the name of the setting by extra-
to append to the previous value.
For instance,
substituters = a b
extra-substituters = c d
defines the substituters
setting to be a b c d
.
Unknown option names are not an error, and are simply ignored with a warning.
Command line flags
Configuration options can be set on the command line, overriding the values set in the configuration file:
-
Every configuration setting has corresponding command line flag (e.g.
--max-jobs 16
). Boolean settings do not need an argument, and can be explicitly disabled with theno-
prefix (e.g.--keep-failed
and--no-keep-failed
).Unknown option names are invalid flags (unless there is already a flag with that name), and are rejected with an error.
-
The flag
--option <name> <value>
is interpreted exactly like a<name> = <value>
in a setting file.Unknown option names are ignored with a warning.
The extra-
prefix is supported for settings that take a list of items (e.g. --extra-trusted users alice
or --option extra-trusted-users alice
).
Available settings
-
Warning
This setting is part of an experimental feature.
To change this setting, make sure the
flakes
experimental feature is enabled. For example, include the following innix.conf
:extra-experimental-features = flakes accept-flake-config = ...
Whether to accept nix configuration from a flake without prompting.
Default:
false
-
Access tokens used to access protected GitHub, GitLab, or other locations requiring token-based authentication.
Access tokens are specified as a string made up of space-separated
host=token
values. The specific token used is selected by matching thehost
portion against the "host" specification of the input. The actual use of thetoken
value is determined by the type of resource being accessed:-
Github: the token value is the OAUTH-TOKEN string obtained as the Personal Access Token from the Github server (see https://docs.github.com/en/developers/apps/building-oauth-apps/authorizing-oauth-apps).
-
Gitlab: the token value is either the OAuth2 token or the Personal Access Token (these are different types tokens for gitlab, see https://docs.gitlab.com/12.10/ee/api/README.html#authentication). The
token
value should betype:tokenstring
wheretype
is eitherOAuth2
orPAT
to indicate which type of token is being specified.
Example
~/.config/nix/nix.conf
:access-tokens = github.com=23ac...b289 gitlab.mycompany.com=PAT:A123Bp_Cd..EfG gitlab.com=OAuth2:1jklw3jk
Example
~/code/flake.nix
:input.foo = { type = "gitlab"; host = "gitlab.mycompany.com"; owner = "mycompany"; repo = "pro"; };
This example specifies three tokens, one each for accessing github.com, gitlab.mycompany.com, and gitlab.com.
The
input.foo
uses the "gitlab" fetcher, which might requires specifying the token type along with the token value.Default: empty
-
-
Whether to allow dirty Git/Mercurial trees.
Default:
true
-
By default, Nix allows Import from Derivation.
With this option set to
false
, Nix will throw an error when evaluating an expression that uses this feature, even when the required store object is readily available. This ensures that evaluation will not require any builds to take place, regardless of the state of the store.Default:
true
-
(Linux-specific.) By default, builders on Linux cannot acquire new privileges by calling setuid/setgid programs or programs that have file capabilities. For example, programs such as
sudo
orping
will fail. (Note that in sandbox builds, no such programs are available unless you bind-mount them into the sandbox via thesandbox-paths
option.) You can allow the use of such programs by enabling this option. This is impure and usually undesirable, but may be useful in certain scenarios (e.g. to spin up containers or set up userspace network interfaces in tests).Default:
false
-
If set to
true
, Nix will stop complaining if the store directory (typically /nix/store) contains symlink components.This risks making some builds "impure" because builders sometimes "canonicalise" paths by resolving all symlink components. Problems occur if those builds are then deployed to machines where /nix/store resolves to a different location from that of the build machine. You can enable this setting if you are sure you're not going to do that.
Default:
false
-
allow-unsafe-native-code-during-evaluation
Whether builtin functions that allow executing native code should be enabled.
Default:
false
-
Which prefixes to allow derivations to ask for access to (primarily for Darwin).
Default: empty
-
A list of URI prefixes to which access is allowed in restricted evaluation mode. For example, when set to
https://github.com/NixOS
, builtin functions such asfetchGit
are allowed to accesshttps://github.com/NixOS/patchelf.git
.Access is granted when
- the URI is equal to the prefix,
- or the URI is a subpath of the prefix,
- or the prefix is a URI scheme ended by a colon
:
and the URI has the same scheme.
Default: empty
-
A list user names, separated by whitespace. These users are allowed to connect to the Nix daemon.
You can specify groups by prefixing names with
@
. For instance,@wheel
means all users in thewheel
group. Also, you can allow all users by specifying*
.Note
Trusted users (set in
trusted-users
) can always connect to the Nix daemon.Default:
*
-
If set to
true
, Nix will ignore theallowSubstitutes
attribute in derivations and always attempt to use available substituters.Default:
false
-
Warning
This setting is part of an experimental feature.
To change this setting, make sure the
auto-allocate-uids
experimental feature is enabled. For example, include the following innix.conf
:extra-experimental-features = auto-allocate-uids auto-allocate-uids = ...
Whether to select UIDs for builds automatically, instead of using the users in
build-users-group
.UIDs are allocated starting at 872415232 (0x34000000) on Linux and 56930 on macOS.
Default:
false
-
If set to
true
, Nix automatically detects files in the store that have identical contents, and replaces them with hard links to a single copy. This saves disk space. If set tofalse
(the default), you can still runnix-store --optimise
to get rid of duplicate files.Default:
false
-
The bash prompt (
PS1
) innix develop
shells.Default: empty
-
Prefix prepended to the
PS1
environment variable innix develop
shells.Default: empty
-
Suffix appended to the
PS1
environment variable innix develop
shells.Default: empty
-
The path to the helper program that executes remote builds.
Nix communicates with the build hook over
stdio
using a custom protocol to request builds that cannot be performed directly by the Nix daemon. The default value is the internal Nix binary that implements remote building.Important
Change this setting only if you really know what you’re doing.
Default: empty
-
How often (in seconds) to poll for locks.
Default:
5
-
This options specifies the Unix group containing the Nix build user accounts. In multi-user Nix installations, builds should not be performed by the Nix account since that would allow users to arbitrarily modify the Nix store and database by supplying specially crafted builders; and they cannot be performed by the calling user since that would allow him/her to influence the build result.
Therefore, if this option is non-empty and specifies a valid group, builds will be performed under the user accounts that are a member of the group specified here (as listed in
/etc/group
). Those user accounts should not be used for any other purpose!Nix will never run two builds under the same user account at the same time. This is to prevent an obvious security hole: a malicious user writing a Nix expression that modifies the build result of a legitimate Nix expression being built by another user. Therefore it is good to have as many Nix build user accounts as you can spare. (Remember: uids are cheap.)
The build users should have permission to create files in the Nix store, but not delete them. Therefore,
/nix/store
should be owned by the Nix account, its group should be the group specified here, and its mode should be1775
.If the build users group is empty, builds will be performed under the uid of the Nix process (that is, the uid of the caller if
NIX_REMOTE
is empty, the uid under which the Nix daemon runs ifNIX_REMOTE
isdaemon
). Obviously, this should not be used with a nix daemon accessible to untrusted clients.Defaults to
nixbld
when running as root, empty otherwise.Default: machine-specific
-
A semicolon- or newline-separated list of build machines.
In addition to the usual ways of setting configuration options, the value can be read from a file by prefixing its absolute path with
@
.Example
This is the default setting:
builders = @/etc/nix/machines
Each machine specification consists of the following elements, separated by spaces. Only the first element is required. To leave a field at its default, set it to
-
.-
The URI of the remote store in the format
ssh://[username@]hostname
.Example
ssh://nix@mac
For backward compatibility,
ssh://
may be omitted. The hostname may be an alias defined in~/.ssh/config
. -
A comma-separated list of Nix system types. If omitted, this defaults to the local platform type.
Example
aarch64-darwin
It is possible for a machine to support multiple platform types.
Example
i686-linux,x86_64-linux
-
The SSH identity file to be used to log in to the remote machine. If omitted, SSH will use its regular identities.
Example
/home/user/.ssh/id_mac
-
The maximum number of builds that Nix will execute in parallel on the machine. Typically this should be equal to the number of CPU cores.
-
The “speed factor”, indicating the relative speed of the machine as a positive integer. If there are multiple machines of the right type, Nix will prefer the fastest, taking load into account.
-
A comma-separated list of supported system features.
A machine will only be used to build a derivation if all the features in the derivation's
requiredSystemFeatures
attribute are supported by that machine. -
A comma-separated list of required system features.
A machine will only be used to build a derivation if all of the machine’s required features appear in the derivation’s
requiredSystemFeatures
attribute. -
The (base64-encoded) public host key of the remote machine. If omitted, SSH will use its regular
known_hosts
file.The value for this field can be obtained via
base64 -w0
.
Example
Multiple builders specified on the command line:
--builders 'ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd'
Example
This specifies several machines that can perform
i686-linux
builds:nix@scratchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy 8 1 kvm nix@itchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy 8 2 nix@poochie.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy 1 2 kvm benchmark
However,
poochie
will only build derivations that have the attributerequiredSystemFeatures = [ "benchmark" ];
or
requiredSystemFeatures = [ "benchmark" "kvm" ];
itchy
cannot do builds that requirekvm
, butscratchy
does support such builds. For regular builds,itchy
will be preferred overscratchy
because it has a higher speed factor.For Nix to use substituters, the calling user must be in the
trusted-users
list.Note
A build machine must be accessible via SSH and have Nix installed.
nix
must be available in$PATH
for the user connecting over SSH.Warning
If you are building via the Nix daemon (default), the Nix daemon user account on the local machine (that is,
root
) requires access to a user account on the remote machine (not necessarilyroot
).If you can’t or don’t want to configure
root
to be able to access the remote machine, setstore
to any local store, e.g. by passing--store /tmp
to the command on the local machine.To build only on remote machines and disable local builds, set
max-jobs
to 0.If you want the remote machines to use substituters, set
builders-use-substitutes
totrue
.Default: machine-specific
-
-
If set to
true
, Nix will instruct remote build machines to use their ownsubstituters
if available.It means that remote build hosts will fetch as many dependencies as possible from their own substituters (e.g, from
cache.nixos.org
) instead of waiting for the local machine to upload them all. This can drastically reduce build times if the network connection between the local machine and the remote build host is slow.Default:
false
-
Warning
This setting is part of an experimental feature.
To change this setting, make sure the
flakes
experimental feature is enabled. For example, include the following innix.conf
:extra-experimental-features = flakes commit-lockfile-summary = ...
The commit summary to use when committing changed flake lock files. If empty, the summary is generated based on the action performed.
Default: empty
-
If set to
true
(the default), build logs written to/nix/var/log/nix/drvs
will be compressed on the fly using bzip2. Otherwise, they will not be compressed.Default:
true
Deprecated alias:
build-compress-log
-
The timeout (in seconds) for establishing connections in the binary cache substituter. It corresponds to
curl
’s--connect-timeout
option. A value of 0 means no limit.Default:
0
-
Sets the value of the
NIX_BUILD_CORES
environment variable in the invocation of thebuilder
executable of a derivation. Thebuilder
executable can use this variable to control its own maximum amount of parallelism.For instance, in Nixpkgs, if the attribute
enableParallelBuilding
for themkDerivation
build helper is set totrue
, it will pass the-j${NIX_BUILD_CORES}
flag to GNU Make.The value
0
means that thebuilder
should use all available CPU cores in the system.Note
The number of parallel local Nix build jobs is independently controlled with the
max-jobs
setting.Default: machine-specific
Deprecated alias:
build-cores
-
If set to true and the
--debugger
flag is given,builtins.trace
will enter the debugger likebuiltins.break
.This is useful for debugging warnings in third-party Nix code.
Default:
false
-
Absolute path to an executable capable of diffing build results. The hook is executed if
run-diff-hook
is true, and the output of a build is known to not be the same. This program is not executed to determine if two results are the same.The diff hook is executed by the same user and group who ran the build. However, the diff hook does not have write access to the store path just built.
The diff hook program receives three parameters:
-
A path to the previous build's results
-
A path to the current build's results
-
The path to the build's derivation
-
The path to the build's scratch directory. This directory will exist only if the build was run with
--keep-failed
.
The stderr and stdout output from the diff hook will not be displayed to the user. Instead, it will print to the nix-daemon's log.
When using the Nix daemon,
diff-hook
must be set in thenix.conf
configuration file, and cannot be passed at the command line.Default: ``
-
-
How often Nix will attempt to download a file before giving up.
Default:
5
-
Specify the maximum transfer rate in kilobytes per second you want Nix to use for downloads.
Default:
0
-
Whether to use the flake evaluation cache.
Default:
true
-
This option defines
builtins.currentSystem
in the Nix language if it is set as a non-empty string. Otherwise, if it is defined as the empty string (the default), the value of thesystem
configuration setting is used instead.Unlike
system
, this setting does not change what kind of derivations can be built locally. This is useful for evaluating Nix code on one system to produce derivations to be built on another type of system.Default: empty
-
Experimental features that are enabled.
Example:
experimental-features = nix-command flakes
The following experimental features are available:
auto-allocate-uids
ca-derivations
cgroups
configurable-impure-env
daemon-trust-override
dynamic-derivations
fetch-closure
fetch-tree
flakes
git-hashing
impure-derivations
mounted-ssh-store
nix-command
no-url-literals
parse-toml-timestamps
read-only-local-store
recursive-nix
repl-flake
verified-fetches
Experimental features are further documented in the manual.
Default: empty
-
System types of executables that can be run on this machine.
Nix will only build a given derivation locally when its
system
attribute equals any of the values specified here or in thesystem
option.Setting this can be useful to build derivations locally on compatible machines:
i686-linux
executables can be run onx86_64-linux
machines (set by default)x86_64-darwin
executables can be run on macOSaarch64-darwin
with Rosetta 2 (set by default where applicable)armv6
andarmv5tel
executables can be run onarmv7
- some
aarch64
machines can also natively run 32-bit ARM code qemu-user
may be used to support non-native platforms (though this may be slow and buggy)
Build systems will usually detect the target platform to be the current physical system and therefore produce machine code incompatible with what may be intended in the derivation. You should design your derivation's
builder
accordingly and cross-check the results when using this option against natively-built versions of your derivation.Default: machine-specific
-
If set to
true
, Nix will fall back to building from source if a binary substitute fails. This is equivalent to the--fallback
flag. The default isfalse
.Default:
false
Deprecated alias:
build-fallback
-
Whether to prevent certain dangerous system calls, such as creation of setuid/setgid files or adding ACLs or extended attributes. Only disable this if you're aware of the security implications.
Default:
true
-
Warning
This setting is part of an experimental feature.
To change this setting, make sure the
flakes
experimental feature is enabled. For example, include the following innix.conf
:extra-experimental-features = flakes flake-registry = ...
Path or URI of the global flake registry.
When empty, disables the global flake registry.
Default:
https://channels.nixos.org/flake-registry.json
-
If set to
true
, changes to the Nix store metadata (in/nix/var/nix/db
) are synchronously flushed to disk. This improves robustness in case of system crashes, but reduces performance. The default istrue
.Default:
true
-
Amount of reserved disk space for the garbage collector.
Default:
8388608
-
A list of web servers used by
builtins.fetchurl
to obtain files by hash. Given a hash algorithm ha and a base-16 hash h, Nix will try to download the file from hashed-mirror/ha/h. This allows files to be downloaded even if they have disappeared from their original URI. For example, given an example mirrorhttp://tarballs.nixos.org/
, when building the derivationbuiltins.fetchurl { url = "https://example.org/foo-1.2.3.tar.xz"; sha256 = "2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae"; }
Nix will attempt to download this file from
http://tarballs.nixos.org/sha256/2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae
first. If it is not available there, if will try the original URI.Default: empty
-
The maximum number of parallel TCP connections used to fetch files from binary caches and by other downloads. It defaults to 25. 0 means no limit.
Default:
25
Deprecated alias:
binary-caches-parallel-connections
-
Whether to enable HTTP/2 support.
Default:
true
-
The number of UIDs/GIDs to use for dynamic ID allocation.
Default:
8388608
-
If set to true, ignore exceptions inside 'tryEval' calls when evaluating nix expressions in debug mode (using the --debugger flag). By default the debugger will pause on all exceptions.
Default:
false
-
A list of ACLs that should be ignored, normally Nix attempts to remove all ACLs from files and directories in the Nix store, but some ACLs like
security.selinux
orsystem.nfs4_acl
can't be removed even by root. Therefore it's best to just ignore them.Default:
security.csm security.selinux system.nfs4_acl
-
Whether to impersonate a Linux 2.6 machine on newer kernels.
Default:
false
Deprecated alias:
build-impersonate-linux-26
-
Warning
This setting is part of an experimental feature.
To change this setting, make sure the
configurable-impure-env
experimental feature is enabled. For example, include the following innix.conf
:extra-experimental-features = configurable-impure-env impure-env = ...
A list of items, each in the format of:
name=value
: Set environment variablename
tovalue
.
If the user is trusted (see
trusted-users
option), when building a fixed-output derivation, environment variables set in this option will be passed to the builder if they are listed inimpureEnvVars
.This option is useful for, e.g., setting
https_proxy
for fixed-output derivations and in a multi-user Nix installation, or setting private access tokens when fetching a private repository.Default: empty
-
If set to
true
(the default), Nix will write the build log of a derivation (i.e. the standard output and error of its builder) to the directory/nix/var/log/nix/drvs
. The build log can be retrieved using the commandnix-store -l path
.Default:
true
Deprecated alias:
build-keep-log
-
If
true
(default), the garbage collector will keep the derivations from which non-garbage store paths were built. Iffalse
, they will be deleted unless explicitly registered as a root (or reachable from other roots).Keeping derivation around is useful for querying and traceability (e.g., it allows you to ask with what dependencies or options a store path was built), so by default this option is on. Turn it off to save a bit of disk space (or a lot if
keep-outputs
is also turned on).Default:
true
Deprecated alias:
gc-keep-derivations
-
If
false
(default), derivations are not stored in Nix user environments. That is, the derivations of any build-time-only dependencies may be garbage-collected.If
true
, when you add a Nix derivation to a user environment, the path of the derivation is stored in the user environment. Thus, the derivation will not be garbage-collected until the user environment generation is deleted (nix-env --delete-generations
). To prevent build-time-only dependencies from being collected, you should also turn onkeep-outputs
.The difference between this option and
keep-derivations
is that this one is “sticky”: it applies to any user environment created while this option was enabled, whilekeep-derivations
only applies at the moment the garbage collector is run.Default:
false
Deprecated alias:
env-keep-derivations
-
Whether to keep temporary directories of failed builds.
Default:
false
-
Whether to keep building derivations when another build fails.
Default:
false
-
If
true
, the garbage collector will keep the outputs of non-garbage derivations. Iffalse
(default), outputs will be deleted unless they are GC roots themselves (or reachable from other roots).In general, outputs must be registered as roots separately. However, even if the output of a derivation is registered as a root, the collector will still delete store paths that are used only at build time (e.g., the C compiler, or source tarballs downloaded from the network). To prevent it from doing so, set this option to
true
.Default:
false
Deprecated alias:
gc-keep-outputs
-
The number of lines of the tail of the log to show if a build fails.
Default:
25
-
This option defines the maximum number of bytes that a builder can write to its stdout/stderr. If the builder exceeds this limit, it’s killed. A value of
0
(the default) means that there is no limit.Default:
0
Deprecated alias:
build-max-log-size
-
The maximum function call depth to allow before erroring.
Default:
10000
-
When a garbage collection is triggered by the
min-free
option, it stops as soon asmax-free
bytes are available. The default is infinity (i.e. delete all garbage).Default:
-1
-
Maximum number of jobs that Nix will try to build locally in parallel.
The special value
auto
causes Nix to use the number of CPUs in your system. Use0
to disable local builds and directly use the remote machines specified inbuilders
. This will not affect derivations that havepreferLocalBuild = true
, which are always built locally.Note
The number of CPU cores to use for each build job is independently determined by the
cores
setting.The setting can be overridden using the
--max-jobs
(-j
) command line switch.Default:
1
Deprecated alias:
build-max-jobs
-
This option defines the maximum number of seconds that a builder can go without producing any data on standard output or standard error. This is useful (for instance in an automated build system) to catch builds that are stuck in an infinite loop, or to catch remote builds that are hanging due to network problems. It can be overridden using the
--max-silent-time
command line switch.The value
0
means that there is no timeout. This is also the default.Default:
0
Deprecated alias:
build-max-silent-time
-
This option defines the maximum number of substitution jobs that Nix will try to run in parallel. The default is
16
. The minimum value one can choose is1
and lower values will be interpreted as1
.Default:
16
Deprecated alias:
substitution-max-jobs
-
When free disk space in
/nix/store
drops belowmin-free
during a build, Nix performs a garbage-collection untilmax-free
bytes are available or there is no more garbage. A value of0
(the default) disables this feature.Default:
0
-
Number of seconds between checking free disk space.
Default:
5
-
Maximum size of NARs before spilling them to disk.
Default:
33554432
-
The TTL in seconds for negative lookups. If a store path is queried from a substituter but was not found, there will be a negative lookup cached in the local disk cache database for the specified duration.
Set to
0
to force updating the lookup cache.To wipe the lookup cache completely:
$ rm $HOME/.cache/nix/binary-cache-v*.sqlite* # rm /root/.cache/nix/binary-cache-v*.sqlite*
Default:
3600
-
The TTL in seconds for positive lookups. If a store path is queried from a substituter, the result of the query will be cached in the local disk cache database including some of the NAR metadata. The default TTL is a month, setting a shorter TTL for positive lookups can be useful for binary caches that have frequent garbage collection, in which case having a more frequent cache invalidation would prevent trying to pull the path again and failing with a hash mismatch if the build isn't reproducible.
Default:
2592000
-
If set to an absolute path to a
netrc
file, Nix will use the HTTP authentication credentials in this file when trying to download from a remote host through HTTP or HTTPS. Defaults to$NIX_CONF_DIR/netrc
.The
netrc
file consists of a list of accounts in the following format:machine my-machine login my-username password my-password
For the exact syntax, see the
curl
documentation.Note
This must be an absolute path, and
~
is not resolved. For example,~/.netrc
won't resolve to your home directory's.netrc
.Default:
/dummy/netrc
-
List of search paths to use for lookup path resolution. This setting determines the value of
builtins.nixPath
and can be used withbuiltins.findFile
.The default value is
$HOME/.nix-defexpr/channels nixpkgs=$NIX_STATE_DIR/profiles/per-user/root/channels/nixpkgs $NIX_STATE_DIR/profiles/per-user/root/channels
It can be overridden with the
NIX_PATH
environment variable or the-I
command line option.Note
If pure evaluation is enabled,
nixPath
evaluates to the empty list[ ]
.Default: machine-specific
-
A list of plugin files to be loaded by Nix. Each of these files will be dlopened by Nix, allowing them to affect execution through static initialization. In particular, these plugins may construct static instances of RegisterPrimOp to add new primops or constants to the expression language, RegisterStoreImplementation to add new store implementations, RegisterCommand to add new subcommands to the
nix
command, and RegisterSetting to add new nix config settings. See the constructors for those types for more details.Warning! These APIs are inherently unstable and may change from release to release.
Since these files are loaded into the same address space as Nix itself, they must be DSOs compatible with the instance of Nix running at the time (i.e. compiled against the same headers, not linked to any incompatible libraries). They should not be linked to any Nix libs directly, as those will be available already at load time.
If an entry in the list is a directory, all files in the directory are loaded as plugins (non-recursively).
Default: empty
-
Optional. The path to a program to execute after each build.
This option is only settable in the global
nix.conf
, or on the command line by trusted users.When using the nix-daemon, the daemon executes the hook as
root
. If the nix-daemon is not involved, the hook runs as the user executing the nix-build.-
The hook executes after an evaluation-time build.
-
The hook does not execute on substituted paths.
-
The hook's output always goes to the user's terminal.
-
If the hook fails, the build succeeds but no further builds execute.
-
The hook executes synchronously, and blocks other builds from progressing while it runs.
The program executes with no arguments. The program's environment contains the following environment variables:
-
DRV_PATH
The derivation for the built paths.Example:
/nix/store/5nihn1a7pa8b25l9zafqaqibznlvvp3f-bash-4.4-p23.drv
-
OUT_PATHS
Output paths of the built derivation, separated by a space character.Example:
/nix/store/zf5lbh336mnzf1nlswdn11g4n2m8zh3g-bash-4.4-p23-dev /nix/store/rjxwxwv1fpn9wa2x5ssk5phzwlcv4mna-bash-4.4-p23-doc /nix/store/6bqvbzjkcp9695dq0dpl5y43nvy37pq1-bash-4.4-p23-info /nix/store/r7fng3kk3vlpdlh2idnrbn37vh4imlj2-bash-4.4-p23-man /nix/store/xfghy8ixrhz3kyy6p724iv3cxji088dx-bash-4.4-p23
.
Default: empty
-
-
If set, the path to a program that can set extra derivation-specific settings for this system. This is used for settings that can't be captured by the derivation model itself and are too variable between different versions of the same system to be hard-coded into nix.
The hook is passed the derivation path and, if sandboxes are enabled, the sandbox directory. It can then modify the sandbox and send a series of commands to modify various settings to stdout. The currently recognized commands are:
extra-sandbox-paths
Pass a list of files and directories to be included in the sandbox for this build. One entry per line, terminated by an empty line. Entries have the same format assandbox-paths
.
Default: empty
-
Whether to preallocate files when writing objects with known size.
Default:
false
-
Whether to print what paths need to be built or downloaded.
Default:
true
-
Pure evaluation mode ensures that the result of Nix expressions is fully determined by explicitly declared inputs, and not influenced by external state:
- Restrict file system and network access to files specified by cryptographic hash
- Disable impure constants:
Default:
false
-
require-drop-supplementary-groups
Following the principle of least privilege, Nix will attempt to drop supplementary groups when building with sandboxing.
However this can fail under some circumstances. For example, if the user lacks the
CAP_SETGID
capability. Searchsetgroups(2)
forEPERM
to find more detailed information on this.If you encounter such a failure, setting this option to
false
will let you ignore it and continue. But before doing so, you should consider the security implications carefully. Not dropping supplementary groups means the build sandbox will be less restricted than intended.This option defaults to
true
when the user is root (sinceroot
usually has permissions to call setgroups) andfalse
otherwise.Default:
false
-
If set to
true
(the default), any non-content-addressed path added or copied to the Nix store (e.g. when substituting from a binary cache) must have a signature by a trusted key. A trusted key is one listed intrusted-public-keys
, or a public key counterpart to a private key stored in a file listed insecret-key-files
.Set to
false
to disable signature checking and trust all non-content-addressed paths unconditionally.(Content-addressed paths are inherently trustworthy and thus unaffected by this configuration option.)
Default:
true
-
If set to
true
, the Nix evaluator will not allow access to any files outside ofbuiltins.nixPath
, or to URIs outside ofallowed-uris
.Default:
false
-
If true, enable the execution of the
diff-hook
program.When using the Nix daemon,
run-diff-hook
must be set in thenix.conf
configuration file, and cannot be passed at the command line.Default:
false
-
If set to
true
, builds will be performed in a sandboxed environment, i.e., they’re isolated from the normal file system hierarchy and will only see their dependencies in the Nix store, the temporary build directory, private versions of/proc
,/dev
,/dev/shm
and/dev/pts
(on Linux), and the paths configured with thesandbox-paths
option. This is useful to prevent undeclared dependencies on files in directories such as/usr/bin
. In addition, on Linux, builds run in private PID, mount, network, IPC and UTS namespaces to isolate them from other processes in the system (except that fixed-output derivations do not run in private network namespace to ensure they can access the network).Currently, sandboxing only work on Linux and macOS. The use of a sandbox requires that Nix is run as root (so you should use the “build users” feature to perform the actual builds under different users than root).
If this option is set to
relaxed
, then fixed-output derivations and derivations that have the__noChroot
attribute set totrue
do not run in sandboxes.The default is
true
on Linux andfalse
on all other platforms.Default:
true
Deprecated alias:
build-use-chroot
,build-use-sandbox
-
The build directory inside the sandbox.
Default:
/build
-
This option determines the maximum size of the
tmpfs
filesystem mounted on/dev/shm
in Linux sandboxes. For the format, see the description of thesize
option oftmpfs
in mount(8). The default is50%
.Default:
50%
-
Whether to disable sandboxing when the kernel doesn't allow it.
Default:
true
-
A list of paths bind-mounted into Nix sandbox environments. You can use the syntax
target=source
to mount a path in a different location in the sandbox; for instance,/bin=/nix-bin
will mount the path/nix-bin
as/bin
inside the sandbox. If source is followed by?
, then it is not an error if source does not exist; for example,/dev/nvidiactl?
specifies that/dev/nvidiactl
will only be mounted in the sandbox if it exists in the host filesystem.If the source is in the Nix store, then its closure will be added to the sandbox as well.
Depending on how Nix was built, the default value for this option may be empty or provide
/bin/sh
as a bind-mount ofbash
.Default: empty
Deprecated alias:
build-chroot-dirs
,build-sandbox-paths
-
A whitespace-separated list of files containing secret (private) keys. These are used to sign locally-built paths. They can be generated using
nix-store --generate-binary-cache-key
. The corresponding public key can be distributed to other users, who can add it totrusted-public-keys
in theirnix.conf
.Default: empty
-
Whether Nix should print out a stack trace in case of Nix expression evaluation errors.
Default:
false
-
The path of a file containing CA certificates used to authenticate
https://
downloads. Nix by default will use the first of the following files that exists:/etc/ssl/certs/ca-certificates.crt
/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt
The path can be overridden by the following environment variables, in order of precedence:
NIX_SSL_CERT_FILE
SSL_CERT_FILE
Default: empty
-
The timeout (in seconds) for receiving data from servers during download. Nix cancels idle downloads after this timeout's duration.
Default:
300
-
The first UID and GID to use for dynamic ID allocation.
Default:
872415232
-
The URL of the Nix store to use for most operations. See the Store Types section of the manual for supported store types and settings.
Default:
auto
-
If set to
true
(default), Nix will use binary substitutes if available. This option can be disabled to force building from source.Default:
true
Deprecated alias:
build-use-substitutes
-
A list of URLs of Nix stores to be used as substituters, separated by whitespace. A substituter is an additional store from which Nix can obtain store objects instead of building them.
Substituters are tried based on their priority value, which each substituter can set independently. Lower value means higher priority. The default is
https://cache.nixos.org
, which has a priority of 40.At least one of the following conditions must be met for Nix to use a substituter:
- The substituter is in the
trusted-substituters
list - The user calling Nix is in the
trusted-users
list
In addition, each store path should be trusted as described in
trusted-public-keys
Default:
https://cache.nixos.org/
Deprecated alias:
binary-caches
- The substituter is in the
-
Whether to call
sync()
before registering a path as valid.Default:
false
-
The system type of the current Nix installation. Nix will only build a given derivation locally when its
system
attribute equals any of the values specified here or inextra-platforms
.The default value is set when Nix itself is compiled for the system it will run on. The following system types are widely used, as Nix is actively supported on these platforms:
x86_64-linux
x86_64-darwin
i686-linux
aarch64-linux
aarch64-darwin
armv6l-linux
armv7l-linux
In general, you do not have to modify this setting. While you can force Nix to run a Darwin-specific
builder
executable on a Linux machine, the result would obviously be wrong.This value is available in the Nix language as
builtins.currentSystem
if theeval-system
configuration option is set as the empty string.Default:
x86_64-linux
-
A set of system “features” supported by this machine.
This complements the
system
andextra-platforms
configuration options and the correspondingsystem
attribute on derivations.A derivation can require system features in the
requiredSystemFeatures
attribute, and the machine to build the derivation must have them.System features are user-defined, but Nix sets the following defaults:
-
apple-virt
Included on Darwin if virtualization is available.
-
kvm
Included on Linux if
/dev/kvm
is accessible. -
nixos-test
,benchmark
,big-parallel
These historical pseudo-features are always enabled for backwards compatibility, as they are used in Nixpkgs to route Hydra builds to specific machines.
-
ca-derivations
Included by default if the
ca-derivations
experimental feature is enabled.This system feature is implicitly required by derivations with the
__contentAddressed
attribute. -
recursive-nix
Included by default if the
recursive-nix
experimental feature is enabled. -
uid-range
On Linux, Nix can run builds in a user namespace where they run as root (UID 0) and have 65,536 UIDs available. This is primarily useful for running containers such as
systemd-nspawn
inside a Nix build. For an example, seetests/systemd-nspawn/nix
.Included by default on Linux if the
auto-allocate-uids
setting is enabled.
Default: machine-specific
-
-
The number of seconds a downloaded tarball is considered fresh. If the cached tarball is stale, Nix will check whether it is still up to date using the ETag header. Nix will download a new version if the ETag header is unsupported, or the cached ETag doesn't match.
Setting the TTL to
0
forces Nix to always check if the tarball is up to date.Nix caches tarballs in
$XDG_CACHE_HOME/nix/tarballs
.Files fetched via
NIX_PATH
,fetchGit
,fetchMercurial
,fetchTarball
, andfetchurl
respect this TTL.Default:
3600
-
This option defines the maximum number of seconds that a builder can run. This is useful (for instance in an automated build system) to catch builds that are stuck in an infinite loop but keep writing to their standard output or standard error. It can be overridden using the
--timeout
command line switch.The value
0
means that there is no timeout. This is also the default.Default:
0
Deprecated alias:
build-timeout
-
If set to
true
, the Nix evaluator will trace every function call. Nix will print a log message at the "vomit" level for every function entrance and function exit.function-trace entered undefined position at 1565795816999559622 function-trace exited undefined position at 1565795816999581277 function-trace entered /nix/store/.../example.nix:226:41 at 1565795253249935150 function-trace exited /nix/store/.../example.nix:226:41 at 1565795253249941684
The
undefined position
means the function call is a builtin.Use the
contrib/stack-collapse.py
script distributed with the Nix source code to convert the trace logs in to a format suitable forflamegraph.pl
.Default:
false
-
Whether
builtins.traceVerbose
should trace its first argument when evaluated.Default:
false
-
A whitespace-separated list of public keys.
At least one of the following condition must be met for Nix to accept copying a store object from another Nix store (such as a substituter):
- the store object has been signed using a key in the trusted keys list
- the
require-sigs
option has been set tofalse
- the store object is content-addressed
Default:
cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
Deprecated alias:
binary-cache-public-keys
-
A list of Nix store URLs, separated by whitespace. These are not used by default, but users of the Nix daemon can enable them by specifying
substituters
.Unprivileged users (those set in only
allowed-users
but nottrusted-users
) can pass assubstituters
only those URLs listed intrusted-substituters
.Default: empty
Deprecated alias:
trusted-binary-caches
-
A list of user names, separated by whitespace. These users will have additional rights when connecting to the Nix daemon, such as the ability to specify additional substituters, or to import unsigned NARs.
You can also specify groups by prefixing names with
@
. For instance,@wheel
means all users in thewheel
group.Warning
Adding a user to
trusted-users
is essentially equivalent to giving that user root access to the system. For example, the user can access or replace store path contents that are critical for system security.Default:
root
-
Used by
nix upgrade-nix
, the URL of the file that contains the store paths of the latest Nix release.Default:
https://github.com/NixOS/nixpkgs/raw/master/nixos/modules/installer/tools/nix-fallback-paths.nix
-
Whether to enable a Darwin-specific hack for dealing with file name collisions.
Default:
false
-
Whether to execute builds inside cgroups. This is only supported on Linux.
Cgroups are required and enabled automatically for derivations that require the
uid-range
system feature.Default:
false
-
Warning
This setting is part of an experimental feature.
To change this setting, make sure the
flakes
experimental feature is enabled. For example, include the following innix.conf
:extra-experimental-features = flakes use-registries = ...
Whether to use flake registries to resolve flake references.
Default:
true
-
Whether SQLite should use WAL mode.
Default:
true
-
If set to
true
, Nix will conform to the XDG Base Directory Specification for files in$HOME
. The environment variables used to implement this are documented in the Environment Variables section.Warning This changes the location of some well-known symlinks that Nix creates, which might break tools that rely on the old, non-XDG-conformant locations.
In particular, the following locations change:
Old New ~/.nix-profile
$XDG_STATE_HOME/nix/profile
~/.nix-defexpr
$XDG_STATE_HOME/nix/defexpr
~/.nix-channels
$XDG_STATE_HOME/nix/channels
If you already have Nix installed and are using profiles or channels, you should migrate manually when you enable this option. If
$XDG_STATE_HOME
is not set, use$HOME/.local/state/nix
instead of$XDG_STATE_HOME/nix
. This can be achieved with the following shell commands:nix_state_home=${XDG_STATE_HOME-$HOME/.local/state}/nix mkdir -p $nix_state_home mv $HOME/.nix-profile $nix_state_home/profile mv $HOME/.nix-defexpr $nix_state_home/defexpr mv $HOME/.nix-channels $nix_state_home/channels
Default:
false
-
String appended to the user agent in HTTP requests.
Default: empty
-
Whether to warn about dirty Git/Mercurial trees.
Default:
true