Name
nix.conf - Lix configuration file
Description
Lix supports a variety of configuration settings, which are read from configuration files or taken as command line flags.
Configuration file
By default Lix reads settings from the following places, in that order:
-
The system-wide configuration file
sysconfdir/nix/nix.conf(i.e./etc/nix/nix.confon most systems), or$NIX_CONF_DIR/nix.confifNIX_CONF_DIRis set.Values loaded in this file are not forwarded to the Nix daemon. The client assumes that the daemon has already loaded them.
-
If
NIX_USER_CONF_FILESis set, then each path separated by:will be loaded in reverse order.Otherwise it will look for
nix/nix.conffiles inXDG_CONFIG_DIRSandXDG_CONFIG_HOME. If unset,XDG_CONFIG_DIRSdefaults to/etc/xdg, andXDG_CONFIG_HOMEdefaults to$HOME/.configas per XDG Base Directory Specification. -
If
NIX_CONFIGis 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>.
A missing file is an error unless !include is used instead.
Paths in includes and option values are interpreted relative to the current configuration file.
In user configuration files, paths starting with ~/ are tilde expanded (by replacing the tilde by the value of $HOME).
Only user configuration files (like $XDG_CONFIG_HOME/nix/nix.conf or the files listed in $NIX_USER_CONF_FILES) can use tilde paths relative to your home directory.
Configuration listed in the $NIX_CONFIG environment variable may not use relative paths.
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-failedand--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
-
Whether to accept Lix configuration from the
nixConfigattribute of a flake. Doing so as a trusted user allows Nix flakes to gain root access on your machine if they set one of the several trusted-user-only settings that execute commands as root.If set to
true, such configuration will be accepted without asking; this is almost always a very bad idea. Setting this toaskwill prompt the user each time whether to allow a certain configuration option set this way, and offer to optionally remember their choice. When set tofalse, the configuration will be automatically declined.See multi-user installations for more details on the Lix security model.
Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
flakes, is enabled. For example, include the following innix.conf:extra-experimental-features = flakes accept-flake-config = ...Default:
ask -
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=tokenvalues. The specific token used is selected by matching thehostportion against the "host" specification of the input. The actual use of thetokenvalue 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
tokenvalue should betype:tokenstringwheretypeis eitherOAuth2orPATto 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=OAuth2:1jklw3jkExample
~/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.foouses 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, Lix allows you to
importfrom a derivation, allowing building at evaluation time. With this option set to false, Lix will throw an error when evaluating an expression that uses this feature, allowing users to ensure their evaluation will not require any builds to take place.Default:
true -
If set to
true, Lix 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-evaluationEnable built-in functions that allow executing native code.
In particular, this adds:
-
builtins.importNativepath symbolRuns function with symbol from a dynamic shared object (DSO) at path. This may be used to add new builtins to the Nix language. The procedure must have the following signature:
extern "C" typedef void (*ValueInitialiser) (EvalState & state, Value & v); -
builtins.execargumentsExecute a program, where arguments are specified as a list of strings, and parse its output as a Nix expression.
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 asfetchGitare allowed to accesshttps://github.com/NixOS/patchelf.git.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,@wheelmeans all users in thewheelgroup. 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, Lix will ignore theallowSubstitutesattribute in derivations and always attempt to use available substituters. For more information onallowSubstitutes, see the manual chapter on advanced attributes.Default:
false -
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.
Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
auto-allocate-uids, is enabled. For example, include the following innix.conf:extra-experimental-features = auto-allocate-uids auto-allocate-uids = ...Default:
false -
If set to
true, Lix 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 --optimiseto get rid of duplicate files.Default:
false -
The bash prompt (
PS1) innix developshells.Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
nix-command, is enabled. For example, include the following innix.conf:extra-experimental-features = nix-command bash-prompt = ...Default: empty
-
Prefix prepended to the
PS1environment variable innix developshells.Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
nix-command, is enabled. For example, include the following innix.conf:extra-experimental-features = nix-command bash-prompt-prefix = ...Default: empty
-
Suffix appended to the
PS1environment variable innix developshells.Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
nix-command, is enabled. For example, include the following innix.conf:extra-experimental-features = nix-command bash-prompt-suffix = ...Default: empty
-
The directory on the host, in which derivations' temporary build directories are created.
If not set, Lix will use the
buildssubdirectory of its configured state directory. Lix will create this directory automatically with suitable permissions if it does not exist, otherwise its permissions must allow all users to traverse the directory (i.e. it must haveo+xset, in unix parlance) for non-sandboxed builds to work correctly.This is also the location where
--keep-failedleaves its files.If Nix runs without sandbox, or if the platform does not support sandboxing with bind mounts (e.g. macOS), then the
builder's environment will contain this directory, instead of the virtual locationsandbox-build-dir.Important:
build-dirmust not be set to a world-writable directory. Placing temporary build directories in a world-writable place allows other users to access or modify build data that is currently in use. This alone is merely an impurity, but combined with another factor this has allowed malicious derivations to escape the build sandbox.Default:
«nixStateDir»/builds -
The path to the helper program that executes remote builds.
Lix communicates with the build hook over
stdiousing a custom protocol to request builds that cannot be performed directly by the Nix daemon. The default value is the internal Lix binary that implements remote building.Warning Change this setting only if you really know what you’re doing.
Warning This setting is deprecated and will be removed in a future version of Lix.
Default: empty
-
How often (in seconds) to poll for locks.
Default:
5 -
This options specifies the Unix group containing the Lix build user accounts. In multi-user Lix installations, builds should not be performed by the Lix 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 them 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!Lix 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 Lix 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/storeshould 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 Lix process (that is, the uid of the caller if both
NIX_REMOTEis either empty orautoand the Nix store is owned by that user, or, alternatively, the uid under which the Nix daemon runs ifNIX_REMOTEisdaemonor if it isautoand the store is not owned by the caller). Obviously, this should not be used with a nix daemon accessible to untrusted clients.For the avoidance of doubt, explicitly setting this to empty with a Lix daemon running as root means that builds will be executed as root with respect to the rest of the system. We intend to fix this: https://git.lix.systems/lix-project/lix/issues/242
Default: running as root:
nixbld, otherwise: empty -
A semicolon-separated list of build machines. For the exact format and examples, see the manual chapter on remote builds
Defaults to
@$NIX_CONF_DIR/machines. The default shown below is only accurate when the value ofNIX_CONF_DIRhas not been overridden at build time or using the environment variable.Default:
@/etc/nix/machines -
If set to
true, Lix will instruct remote build machines to use their own binary substitutes if available. In practical terms, this means that remote hosts will fetch as many build dependencies as possible from their own substitutes (e.g, fromcache.nixos.org), instead of waiting for this host to upload them all. This can drastically reduce build times if the network connection between this computer and the remote build host is slow.Default:
false -
The commit summary to use when committing changed flake lock files. If empty, the summary is generated based on the action performed.
Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
flakes, is enabled. For example, include the following innix.conf:extra-experimental-features = flakes commit-lockfile-summary = ...Default: empty
-
If set to
true(the default), build logs written to/nix/var/log/nix/drvswill be compressed on the fly using bzip2. Otherwise, they will not be compressed.Default:
trueDeprecated alias:
build-compress-log -
The timeout (in seconds) for establishing connections in the binary cache substituter. It corresponds to
curl’s--connect-timeoutoption. A value of 0 means no limit.Default:
5 -
Sets the value of the
NIX_BUILD_CORESenvironment 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 attributeenableParallelBuildingis set totrue, the builder passes the-jNflag to GNU Make. It can be overridden using the--corescommand line switch and defaults to1. The value0means that the builder should use all available CPU cores in the system.Default: machine-specific
Deprecated alias:
build-cores -
Whether to log Darwin sandbox access violations to the system log.
Note This setting is only available on Darwin systems.
Default:
false -
If set to true and the
--debuggerflag is given,builtins.tracewill enter the debugger likebuiltins.break.This is useful for debugging warnings in third-party Nix code.
Default:
false -
Deprecated features that are allowed.
Example:
deprecated-features = url-literalsThe following deprecated feature features can be re-activated:
Deprecated features are further documented in the manual.
Default: empty
-
Path to an executable capable of diffing build results. The hook is executed if
run-diff-hookis 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-hookmust be set in thenix.confconfiguration file, and cannot be passed at the command line.Default: empty
-
-
How often Lix will attempt to download a file before giving up.
Default:
5 -
Specify the maximum transfer rate in kilobytes per second you want Lix to use for downloads.
Default:
0 -
If set to
false(the default),RLIMIT_COREhas a soft limit of zero. If set totrue, the soft limit is infinite.The hard limit is always infinite.
Default:
false -
Whether to use the flake evaluation cache.
Default:
true -
This option defines
builtins.currentSystemin 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 thesystemconfiguration 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 flakesThe following experimental features are available:
auto-allocate-uidsca-derivationscgroupsdaemon-trust-overridedynamic-derivationsfetch-closureflakesimpure-derivationslix-custom-sub-commandsnix-commandno-url-literalsparse-toml-timestampspipe-operatorread-only-local-storerepl-automation
Experimental features are further documented in the manual.
Default: empty
-
System types of executables that can be run on this machine.
Lix will only build a given derivation locally when its
systemattribute equals any of the values specified here or in thesystemoption.Setting this can be useful to build derivations locally on compatible machines:
i686-linuxexecutables can be run onx86_64-linuxmachines (set by default)x86_64-darwinexecutables can be run on macOSaarch64-darwinwith Rosetta 2 (set by default where applicable)armv6andarmv5telexecutables can be run onarmv7- some
aarch64machines can also natively run 32-bit ARM code qemu-usermay 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
builderaccordingly and cross-check the results when using this option against natively-built versions of your derivation.Default: machine-specific
-
If set to
true, Lix will fall back to building from source if a binary substitute fails. This is equivalent to the--fallbackflag. The default isfalse.Default:
falseDeprecated alias:
build-fallback -
Path or URI of the global flake registry.
URIs are deprecated. When set to 'vendored', defaults to a vendored copy of https://channels.nixos.org/flake-registry.json.
When empty, disables the global flake registry.
Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
flakes, is enabled. For example, include the following innix.conf:extra-experimental-features = flakes flake-registry = ...Default:
vendored -
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.fetchurlto obtain files by hash. Given a hash type ht and a base-16 hash h, Lix will try to download the file from hashed-mirror/ht/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"; }Lix will attempt to download this file from
http://tarballs.nixos.org/sha256/2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7aefirst. 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:
25Deprecated alias:
binary-caches-parallel-connections -
Whether to enable HTTP/2 support.
Default:
true -
The number of UIDs/GIDs to use for dynamic ID allocation.
Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
auto-allocate-uids, is enabled. For example, include the following innix.conf:extra-experimental-features = auto-allocate-uids id-count = ...Default: Linux:
8388608, other platforms:128 -
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 Lix attempts to remove all ACLs from files and directories in the Nix store, but some ACLs like
security.selinuxorsystem.nfs4_aclcan't be removed even by root. Therefore it's best to just ignore them.Note This setting is only available on Linux systems.
Default:
security.csm security.selinux system.nfs4_acl -
Whether to impersonate a Linux 2.6 machine on newer kernels.
Note This setting is only available on Linux systems.
Default:
falseDeprecated alias:
build-impersonate-linux-26 -
If set to
true(the default), Lix 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:
trueDeprecated 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-outputsis also turned on).Default:
trueDeprecated 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-derivationsis that this one is “sticky”: it applies to any user environment created while this option was enabled, whilekeep-derivationsonly applies at the moment the garbage collector is run.Default:
falseDeprecated 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:
falseDeprecated 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:
0Deprecated 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-freeoption, it stops as soon asmax-freebytes are available. The default is infinity (i.e. delete all garbage).Default: infinity
-
This option defines the maximum number of jobs that Lix will try to build in parallel. The default is
1. The special valueautocauses Lix to use the number of CPUs in your system.0is useful when using remote builders to prevent any local builds (except forpreferLocalBuildderivation attribute which executes locally regardless). It can be overridden using the--max-jobs(-j) command line switch.Default:
1Deprecated 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-timecommand line switch.The value
0means that there is no timeout. This is also the default.Default:
0Deprecated 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 is1and lower values will be interpreted as1.Default:
16Deprecated alias:
substitution-max-jobs -
When free disk space in
/nix/storedrops belowmin-freeduring a build, Lix performs a garbage-collection untilmax-freebytes 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.
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
netrcfile, Lix will use the HTTP authentication credentials in this file when trying to download from a remote host through HTTP or HTTPS.The
netrcfile consists of a list of accounts in the following format:machine my-machine login my-username password my-passwordFor the exact syntax, see the
curldocumentation.Note
This must be an absolute path, and
~is not resolved. For example,~/.netrcwon't resolve to your home directory's.netrc.Defaults to
$NIX_CONF_DIR/netrc. The default shown below is only accurate when the value ofNIX_CONF_DIRhas not been overridden at build time or using the environment variable.Default:
/etc/nix/netrc -
List of directories to be searched for
<...>file referencesIn particular, outside of pure evaluation mode, this determines the value of
builtins.nixPath.Default: machine-specific
-
If set to an absolute path, enables fully sandboxing fixed-output derivations, by using
pastato pass network traffic between the private network namespace. This allows for greater levels of isolation of builds to the host.Default: empty
-
A list of plugin files to be loaded by Lix.
Each of these files will be
dlopened by Lix, allowing them to affect execution by registering various entities in Lix. After the plugins are loaded, they will have the function within them with signatureextern "C" void nix_plugin_entry(void)called if it is defined.If an entry in the list is a directory, all files in the directory are loaded as plugins (non-recursively).
FIXME(jade): We should provide a
nix_plugin_finalize()that gets called at some point in teardown for use cases like nix-otel which need to be able to cleanup, flush things to network, etc, on exit without having to do that from life-after-main().In particular, these plugins may:
- Construct static instances of
RegisterPrimOpto add new primops or constants to the expression language (FIXME: will be replaced with an explicit function). - Add new store implementations with
StoreImplementations::add. - Construct static instances of
RegisterCommandto add new subcommands to thenixcommand (FIXME: will be replaced with an explicit function). - Construct static instances of
Settingto add new Lix settings (FIXME: will be replaced with an explicit function).
See the documentation for those symbols for more details. Note all the FIXMEs above: Lix is removing its usages of static initializers, see https://git.lix.systems/lix-project/lix/issues/359.
Warning! These APIs are inherently unstable and may change in minor versions. It's recommended to, if you are relying on Lix's unstable C++ API, develop against Lix
main, runmainyourself, and be active in Lix development.Since these files are loaded into the same address space as Lix itself, they must be DSOs compatible with the instance of Lix running at the time (i.e. compiled against the same headers, not linked to any incompatible libraries, produced by the same nixpkgs).
It's recommended that this setting not be used in
nix.confsince it is almost always the case that there are multiple versions of the Nix implementation on a machine. In particular, CppNix (still true in 2.26 as of this writing) considers plugin load failure to be a hard error unlike Lix (since pre-2.90), which means that puttingplugin-filesinnix.confcauses randomnixexecution failures. Prefer instead to wrap thenixcommand using either theNIX_CONFIGenvironment variable or--option plugin-files.Plugins should not be linked to any Lix libs directly, as those will be available already at load time (FIXME: is it an actual problem if they are, assuming that there are not version mismatches?).
Default: empty
- Construct static instances of
-
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_PATHThe derivation for the built paths.Example:
/nix/store/5nihn1a7pa8b25l9zafqaqibznlvvp3f-bash-4.4-p23.drv -
OUT_PATHSOutput 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.
At the time of running the hook, the derivation may or may not exist on disk (and, e.g. won't exist in the case of many remote builds).
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:
- File system and network access is restricted to accesses to immutable data only:
-
Path literals relative to the home directory like
~/lixare rejected at parse time. -
Access to absolute paths that did not result from Nix language evaluation is rejected when such paths are given as parameters to builtins like, for example,
builtins.readFile.Access is nonetheless allowed to (absolute) paths in the Nix store that are returned by builtins like
builtins.filterSource,builtins.fetchTarballand similar. -
Impure fetches such as not specifying a commit ID for
builtins.fetchGitor not specifying a hash forbuiltins.fetchTarballare rejected. -
In flakes, access to relative paths outside of the root of the flake's source tree (often, a git repository) is rejected.
-
- The evaluator ignores
NIX_PATH,-Iand thenix-pathsetting. Thus,builtins.nixPathis an empty list. - The builtins
builtins.currentSystemandbuiltins.currentTimeare absent frombuiltins. builtins.getEnvalways returns empty string for any variable.builtins.storePaththrows an error (Lix may change this, tracking issue: https://git.lix.systems/lix-project/lix/issues/402)
Default:
false - File system and network access is restricted to accesses to immutable data only:
-
A list of files containing Nix expressions that can be used to add default bindings to
nix replsessions.Each file is called with three arguments:
- An attribute set
containing at least a
currentSystemattribute (this is identical tobuiltins.currentSystem, except that it's available inpure-evalmode). - The top-level bindings produced by the previous
repl-overlaysvalue (or the default top-level bindings). - The final top-level bindings produced by calling all
repl-overlays.
For example, the following file would alias
pkgstolegacyPackages.${info.currentSystem}(if that attribute is defined):info: final: prev: if prev ? legacyPackages && prev.legacyPackages ? ${info.currentSystem} then { pkgs = prev.legacyPackages.${info.currentSystem}; } else { }Here's a more elaborate
repl-overlay, which provides the following variables:- The original, unmodified variables are aliased to
original. legacyPackages.${system}(if it exists) orpackages.${system}(otherwise) is aliased topkgs.- All attribute set variables with a
${system}attribute are abbreviated in the same manner; e.g.devShells.${system}is shortened todevShells.
For example, the following attribute set:
info: final: attrs: let # Equivalent to nixpkgs `lib.optionalAttrs`. optionalAttrs = predicate: attrs: if predicate then attrs else {}; # If `attrs.${oldName}.${info.currentSystem}` exists, alias `${newName}` to # it. collapseRenamed = oldName: newName: optionalAttrs (builtins.hasAttr oldName attrs && builtins.hasAttr info.currentSystem attrs.${oldName}) { ${newName} = attrs.${oldName}.${info.currentSystem}; }; # Alias `attrs.${oldName}.${info.currentSystem} to `${newName}`. collapse = name: collapseRenamed name name; # Alias all `attrs` keys with an `${info.currentSystem}` attribute. collapseAll = builtins.foldl' (prev: name: prev // collapse name) {} (builtins.attrNames attrs); in # Preserve the original bindings as `original`. (optionalAttrs (! attrs ? original) { original = attrs; }) // (collapseRenamed "packages" "pkgs") // (collapseRenamed "legacyPackages" "pkgs") // collapseAllDefault: empty
- An attribute set
containing at least a
-
require-drop-supplementary-groupsFollowing the principle of least privilege, Lix 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_SETGIDcapability. Searchsetgroups(2)forEPERMto find more detailed information on this.If you encounter such a failure, setting this option to
falsewill 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.Note This setting is only available on Linux systems.
Default: running as root:
true, otherwise: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
falseto 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 of the Nix search path (as set via theNIX_PATHenvironment variable or the-Ioption), or to URIs outside ofallowed-uris. The default isfalse.Default:
false -
If true, enable the execution of the
diff-hookprogram.When using the Nix daemon,
run-diff-hookmust be set in thenix.confconfiguration 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/shmand/dev/pts(on Linux), and the paths configured with thesandbox-pathsoption. 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 Lix 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__noChrootattribute set totruedo not run in sandboxes.The default is
trueon Linux andfalseon all other platforms.Default: Linux:
true, other platforms:falseDeprecated alias:
build-use-chroot,build-use-sandbox -
The build directory inside the sandbox.
This directory is backed by
build-diron the host.Note This setting is only available on Linux systems.
Default:
/build -
This option determines the maximum size of the
tmpfsfilesystem mounted on/dev/shmin Linux sandboxes. For the format, see the description of thesizeoption oftmpfsin mount(8). The default is50%.Note This setting is only available on Linux systems.
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=sourceto mount a path in a different location in the sandbox; for instance,/bin=/nix-binwill mount the path/nix-binas/bininside 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/nvidiactlwill 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 Lix was built, the default value for this option may be empty or provide
/bin/shas 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-keysin theirnix.conf.Default: empty
-
Whether Lix 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. Lix 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_FILESSL_CERT_FILE
Default: machine-specific
-
The timeout (in seconds) for receiving data from servers during download. Lix cancels idle downloads after this timeout's duration.
Default:
300 -
The first UID and GID to use for dynamic ID allocation.
Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
auto-allocate-uids, is enabled. For example, include the following innix.conf:extra-experimental-features = auto-allocate-uids start-id = ...Default: Linux:
872415232, other platforms:56930 -
The URL of the Nix store to use for most operations. See
nix help-storesfor supported store types and settings.Default:
auto -
If set to
true(default), Lix will use binary substitutes if available. This option can be disabled to force building from source.Default:
trueDeprecated 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 Lix 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 Lix to use a substituter:
- The substituter is in the
trusted-substituterslist - The user calling Lix is in the
trusted-userslist
In addition, each store path should be trusted as described in
trusted-public-keysDefault:
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 Lix installation. Lix will only build a given derivation locally when its
systemattribute equals any of the values specified here or inextra-platforms.The default value is set when Lix itself is compiled for the system it will run on. The following system types are widely used, as Lix is actively supported on these platforms:
x86_64-linuxx86_64-darwini686-linuxaarch64-linuxaarch64-darwinarmv6l-linuxarmv7l-linux
In general, you do not have to modify this setting. While you can force Lix to run a Darwin-specific
builderexecutable on a Linux machine, the result would obviously be wrong.This value is available in the Nix language as
builtins.currentSystemif theeval-systemconfiguration option is set as the empty string.Default: machine-specific
-
A set of system “features” supported by this machine, e.g.
kvm. Derivations can express a dependency on such features through the derivation attributerequiredSystemFeatures. For example, the attributerequiredSystemFeatures = [ "kvm" ];ensures that the derivation can only be built on a machine with the
kvmfeature.This setting by default includes
kvmif/dev/kvmis accessible,apple-virtif hardware virtualization is available on macOS, and the pseudo-featuresnixos-test,benchmarkandbig-parallelthat are used in Nixpkgs to route builds to specific machines.Default: machine-specific
-
The number of seconds a downloaded tarball is considered fresh. If the cached tarball is stale, Lix will check whether it is still up to date using the ETag header. Lix will download a new version if the ETag header is unsupported, or the cached ETag doesn't match.
Setting the TTL to
0forces Lix to always check if the tarball is up to date.Lix caches tarballs in
$XDG_CACHE_HOME/nix/tarballs.Files fetched via
NIX_PATH,fetchGit,fetchMercurial,fetchTarball, andfetchurlrespect this TTL.Default:
3600 -
The directory on the host used as the default temporary directory.
If not set, Nix will use the system temporary directory indicated by the
TMPDIRenvironment variable.This will be used for anything that would otherwise fall back to
TMPDIR, and the inheritedTMPDIRvalue will be preserved for child processes to use. Ifbuild-diris set, that takes precedence over this where it applies.If set, the value must be a path that exists and is accessible to all users.
Default: empty
-
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
--timeoutcommand line switch.The value
0means that there is no timeout. This is also the default.Default:
0Deprecated 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 1565795253249941684The
undefined positionmeans the function call is a builtin.Use the
contrib/stack-collapse.pyscript distributed with the Nix source code to convert the trace logs in to a format suitable forflamegraph.pl.Default:
false -
Whether
builtins.traceVerboseshould 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 Lix 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-sigsoption has been set tofalse - the store object is output-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-usersbut nottrusted-users) can pass assubstitutersonly 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,@wheelmeans all users in thewheelgroup.Warning
Adding a user to
trusted-usersis 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 -
Whether to enable a Darwin-specific hack for dealing with file name collisions.
Default: Darwin:
true, other platforms:false -
Whether to execute builds inside cgroups.
Cgroups are required and enabled automatically for derivations that require the
uid-rangesystem feature.Note This setting is only available on Linux systems.
Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
cgroups, is enabled. For example, include the following innix.conf:extra-experimental-features = cgroups use-cgroups = ...Default:
false -
Whether to use flake registries to resolve flake references.
Warning This setting is part of an experimental feature.
To change this setting, you need to make sure the corresponding experimental feature,
flakes, is enabled. For example, include the following innix.conf:extra-experimental-features = flakes use-registries = ...Default:
true -
Whether SQLite should use WAL mode.
Default: WSL 1:
false, other platforms:true -
If set to
true, Lix 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 Lix 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/channelsIf you already have Lix installed and are using profiles or channels, you should migrate manually when you enable this option. If
$XDG_STATE_HOMEis not set, use$HOME/.local/state/nixinstead 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/channelsDefault:
false -
String appended to the user agent in HTTP requests.
Default: empty
-
Whether to warn about dirty Git/Mercurial trees.
Default:
true