nix.conf

title: nix.conf(5)

text:
# nix.conf(5)

## 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:

1.

The system-wide configuration file sysconfdir/nix/nix.conf (i.e. /etc/nix/nix.conf on most systems), or $NIX_CONF_DIR/nix.conf if NIX_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.

2.

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 in XDG_CONFIG_DIRS and XDG_CONFIG_HOME. If unset, XDG_CONFIG_DIRS defaults to /etc/xdg, and XDG_CONFIG_HOME defaults to $HOME/.config as per XDG Base Directory Specification.

3.

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 the no- 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).

### Integer settings
Settings that have an integer type support the suffixes K, M, G and T. These cause the specified value to be multiplied by 2^10, 2^20, 2^30 and 2^40, respectively. For instance, --min-free 1M is equivalent to --min-free 1048576.

## Available settings
•

abort-on-warn

If set to true, builtins.warn throws an error when logging a warning.

This will give you a stack trace that leads to the location of the warning.

This is useful for finding information about warnings in third-party Nix code when you can not start the interactive debugger, such as when Nix is called from a non-interactive script. See debugger-on-warn.

Currently, a stack trace can only be produced when the debugger is enabled, or when evaluation is aborted.

This option can be enabled by setting NIX_ABORT_ON_WARN=1 in the environment.

Default: false

•

accept-flake-config

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 in nix.conf:

```
extra-experimental-features = flakes
accept-flake-config = ...
```

Whether to accept Nix configuration settings from a flake without prompting.

Default: false

•

access-tokens

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 the host portion against the “host” specification of the input. The host portion may contain a path element which matches against the prefix URL for the input. (eg: github.com/org=token). The actual use of the token 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 be type:tokenstring where type is either OAuth2 or PAT 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

•

allow-dirty

Whether to allow dirty Git/Mercurial trees.

Default: true

•

allow-dirty-locks

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 in nix.conf:

```
extra-experimental-features = flakes
allow-dirty-locks = ...
```

Whether to allow dirty inputs (such as dirty Git workdirs) to be locked via their NAR hash. This is generally bad practice since Nix has no way to obtain such inputs if they are subsequently modified. Therefore lock files with dirty locks should generally only be used for local testing, and should not be pushed to other users.

Default: false

•

allow-import-from-derivation

By default, Nix allows Import from Derivation.

With this option set to false, Nix throws an error when evaluating an expression that uses this feature, even when the required store object is readily available. This ensures that evaluation doesn’t require any builds to take place, regardless of the state of the store.

Default: true

•

allow-new-privileges

(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 or ping should fail. (Note that in sandbox builds, no such programs are available unless you bind-mount them into the sandbox via the sandbox-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

•

allow-symlinked-store

If set to true, Nix stops 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

Enable built-in functions that allow executing native code.

In particular, this adds:

•

builtins.importNative path symbol

Opens dynamic shared object (DSO) at path, loads the function with the symbol name symbol from it and runs it. The loaded function must have the following signature: cpp extern "C" typedef void (*ValueInitialiser) (EvalState & state, Value & v);

The Nix C++ API documentation has more details on evaluator internals.

•

builtins.exec arguments

Execute a program, where arguments are specified as a list of strings, and parse its output as a Nix expression.

Default: false

•

allowed-impure-host-deps

Which prefixes to allow derivations to ask for access to (primarily for Darwin).

Default: empty

•

allowed-uris

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 as fetchGit are allowed to access https://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

•

allowed-users

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 the wheel group. Also, you can allow all users by specifying *.

Note

Trusted users (set in trusted-users) can always connect to the Nix daemon.

Default: *

•

always-allow-substitutes

If set to true, Nix ignores the allowSubstitutes attribute in derivations and always attempt to use available substituters.

Default: false

•

auto-allocate-uids

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 in nix.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

•

auto-optimise-store

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 to false (the default), you can still run nix-store --optimise to get rid of duplicate files.

Default: false

•

bash-prompt

The bash prompt (PS1) in nix develop shells.

Default: empty

•

bash-prompt-prefix

Prefix prepended to the PS1 environment variable in nix develop shells.

Default: empty

•

bash-prompt-suffix

Suffix appended to the PS1 environment variable in nix develop shells.

Default: empty

•

build-dir

Override the build-dir store setting for all stores that have this setting.

Default: ``

•

build-hook

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: nix __build-remote

•

build-poll-interval

How often (in seconds) to poll for locks.

Default: 5

•

build-users-group

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 are 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 never runs 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 be 1775.

If the build users group is empty, builds areperformed 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 if NIX_REMOTE is daemon). 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

•

builders

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 -.

1.

The URI of the remote store in the format ssh://[username@]hostname[:port].

Example

ssh://nix@mac

For backward compatibility, ssh:// may be omitted. The hostname may be an alias defined in ~/.ssh/config.

2.

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

3.

The SSH identity file to be used to log in to the remote machine. If omitted, SSH uses its regular identities.

Example

/home/user/.ssh/id_mac

4.

The maximum number of builds that Nix executes in parallel on the machine. Typically this should be equal to the number of CPU cores.

5.

The “speed factor”, indicating the relative speed of the machine as a positive integer. If there are multiple machines of the right type, Nix prefers the fastest, taking load into account.

6.

A comma-separated list of supported system features.

A machine is only used to build a derivation if all the features in the derivation’s requiredSystemFeatures attribute are supported by that machine.

7.

A comma-separated list of required system features.

A machine is only used to build a derivation if all of the machine’s required features appear in the derivation’s requiredSystemFeatures attribute.

8.

The (base64-encoded) public host key of the remote machine. If omitted, SSH uses 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 only builds derivations that have the attribute

```
requiredSystemFeatures = [ "benchmark" ];
```

or

```
requiredSystemFeatures = [ "benchmark" "kvm" ];
```

itchy cannot do builds that require kvm, but scratchy does support such builds. For regular builds, itchy is preferred over scratchy 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 necessarily root).

If you can’t or don’t want to configure root to be able to access the remote machine, set store 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 to true.

Default: machine-specific

•

builders-use-substitutes

If set to true, Nix instructs remote build machines to use their own substituters if available.

It means that remote build hosts fetches 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

•

commit-lock-file-summary

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 in nix.conf:

```
extra-experimental-features = flakes
commit-lock-file-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

Deprecated alias: commit-lockfile-summary

•

compress-build-log

If set to true (the default), build logs written to /nix/var/log/nix/drvs are compressed on the fly using bzip2. Otherwise, they are not compressed.

Default: true

Deprecated alias: build-compress-log

•

connect-timeout

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: 15

•

cores

Sets the value of the NIX_BUILD_CORES environment variable in the invocation of the builder executable of a derivation. The builder executable can use this variable to control its own maximum amount of parallelism.

For instance, in Nixpkgs, if the attribute enableParallelBuilding for the mkDerivation build helper is set to true, it passes the -j${NIX_BUILD_CORES} flag to GNU Make.

If set to 0, nix will detect the number of CPU cores and pass this number via NIXBUILDCORES.

Note

The number of parallel local Nix build jobs is independently controlled with the max-jobs setting.

Default: 0

Deprecated alias: build-cores

•

debugger-on-trace

If set to true and the --debugger flag is given, the following functions enter the debugger like builtins.break:

- builtins.trace

- builtins.traceVerbose if trace-verbose is set to true.

- builtins.warn

This is useful for debugging warnings in third-party Nix code.

Default: false

•

debugger-on-warn

If set to true and the --debugger flag is given, builtins.warn will enter the debugger like builtins.break.

This is useful for debugging warnings in third-party Nix code.

Use debugger-on-trace to also enter the debugger on legacy warnings that are logged with builtins.trace.

Default: false

•

diff-hook

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:

1.

A path to the previous build’s results

2.

A path to the current build’s results

3.

The path to the build’s derivation

4.

The path to the build’s scratch directory. This directory exists only if the build was run with --keep-failed.

The stderr and stdout output from the diff hook isn’t displayed to the user. Instead, it print to the nix-daemon’s log.

When using the Nix daemon, diff-hook must be set in the nix.conf configuration file, and cannot be passed at the command line.

Default: ``

•

download-attempts

The number of times Nix attempts to download a file before giving up.

Default: 5

•

download-buffer-size

The size of Nix’s internal download buffer in bytes during curl transfers. If data is not processed quickly enough to exceed the size of this buffer, downloads may stall. The default is 67108864 (64 MiB).

Default: 67108864

•

download-speed

Specify the maximum transfer rate in kilobytes per second you want Nix to use for downloads.

Default: 0

•

eval-cache

Whether to use the flake evaluation cache. Certain commands won’t have to evaluate when invoked for the second time with a particular version of a flake. Intermediate results are not cached.

Default: true

•

eval-profile-file

Specifies the file where evaluation profile is saved.

Default: nix.profile

•

eval-profiler

Enables evaluation profiling. The following modes are supported:

•

flamegraph stack sampling profiler. Outputs folded format, one line per stack (suitable for flamegraph.pl and compatible tools).

Use eval-profile-file to specify where the profile is saved.

See Using the eval-profiler.

Default: disabled

•

eval-profiler-frequency

Specifies the sampling rate in hertz for sampling evaluation profilers. Use 0 to sample the stack after each function call. See eval-profiler.

Default: 99

•

eval-system

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 the system 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

Experimental features that are enabled.

Example:

```
experimental-features = nix-command flakes
```

The following experimental features are available:

{{#include experimental-features-shortlist.md}}

Experimental features are further documented in the manual.

Default: empty

•

extra-platforms

System types of executables that can be run on this machine.

Nix only builds a given store derivation locally when its system attribute equals any of the values specified here or in the system option.

Setting this can be useful to build derivations locally on compatible machines:

- i686-linux executables can be run on x86_64-linux machines (set by default)

- x86_64-darwin executables can be run on macOS aarch64-darwin with Rosetta 2 (set by default where applicable)

- armv6 and armv5tel executables can be run on armv7

- 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 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

•

fallback

If set to true, Nix falls back to building from source if a binary substitute fails. This is equivalent to the --fallback flag. The default is false.

Default: false

Deprecated alias: build-fallback

•

filter-syscalls

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

•

flake-registry

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 in nix.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

•

fsync-metadata

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 is true.

Default: true

•

fsync-store-paths

Whether to call fsync() on store paths before registering them, to flush them to disk. This improves robustness in case of system crashes, but reduces performance. The default is false.

Default: false

•

gc-reserved-space

Amount of reserved disk space for the garbage collector.

Default: 8388608

•

hashed-mirrors

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 tries 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 mirror http://tarballs.nixos.org/, when building the derivation

```
builtins.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, it tries the original URI.

Default: empty

•

http-connections

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

•

http2

Whether to enable HTTP/2 support.

Default: true

•

id-count

The number of UIDs/GIDs to use for dynamic ID allocation.

Default: 8388608

•

ignore-try

If set to true, ignore exceptions inside ‘tryEval’ calls when evaluating Nix expressions in debug mode (using the –debugger flag). By default the debugger pauses on all exceptions.

Default: false

•

ignored-acls

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 or system.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

•

impersonate-linux-26

Whether to impersonate a Linux 2.6 machine on newer kernels.

Default: false

Deprecated alias: build-impersonate-linux-26

•

impure-env

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 in nix.conf:

```
extra-experimental-features = configurable-impure-env
impure-env = ...
```

A list of items, each in the format of:

•

name=value: Set environment variable name to value.

If the user is trusted (see trusted-users option), when building a fixed-output derivation, environment variables set in this option is passed to the builder if they are listed in impureEnvVars.

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

•

json-log-path

A file or unix socket to which JSON records of Nix’s log output are written, in the same format as --log-format internal-json (without the @nix prefixes on each line). Concurrent writes to the same file by multiple Nix processes are not supported and may result in interleaved or corrupted log records.

Default: empty

•

keep-build-log

If set to true (the default), Nix writes 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 command nix-store -l path.

Default: true

Deprecated alias: build-keep-log

•

keep-derivations

If true (default), the garbage collector keeps the derivations from which non-garbage store paths were built. If false, they are 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

•

keep-env-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 isn’t 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 on keep-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, while keep-derivations only applies at the moment the garbage collector is run.

Default: false

Deprecated alias: env-keep-derivations

•

keep-failed

Whether to keep temporary directories of failed builds.

Default: false

•

keep-going

Whether to keep building derivations when another build fails.

Default: false

•

keep-outputs

If true, the garbage collector keeps the outputs of non-garbage derivations. If false (default), outputs are 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 still deletes 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

•

log-lines

The number of lines of the tail of the log to show if a build fails.

Default: 25

•

max-build-log-size

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

•

max-call-depth

The maximum function call depth to allow before erroring.

Default: 10000

•

max-free

When a garbage collection is triggered by the min-free option, it stops as soon as max-free bytes are available. The default is infinity (i.e. delete all garbage).

Default: 9223372036854775807

•

max-jobs

Maximum number of jobs that Nix tries to build locally in parallel.

The special value auto causes Nix to use the number of CPUs in your system. Use 0 to disable local builds and directly use the remote machines specified in builders. This doesn’t affect derivations that have preferLocalBuild = 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

•

max-silent-time

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

•

max-substitution-jobs

This option defines the maximum number of substitution jobs that Nix tries to run in parallel. The default is 16. The minimum value one can choose is 1 and lower values are interpreted as 1.

Default: 16

Deprecated alias: substitution-max-jobs

•

min-free

When free disk space in /nix/store drops below min-free during a build, Nix performs a garbage-collection until max-free bytes are available or there is no more garbage. A value of 0 (the default) disables this feature.

Default: 0

•

min-free-check-interval

Number of seconds between checking free disk space.

Default: 5

•

nar-buffer-size

Maximum size of NARs before spilling them to disk.

Default: 33554432

•

narinfo-cache-negative-ttl

The TTL in seconds for negative lookups. If a store path is queried from a substituter but was not found, a negative lookup is 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

•

narinfo-cache-positive-ttl

The TTL in seconds for positive lookups. If a store path is queried from a substituter, the result of the query is 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

•

netrc-file

If set to an absolute path to a netrc file, Nix uses 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

•

nix-path

List of search paths to use for lookup path resolution. This setting determines the value of builtins.nixPath and can be used with builtins.findFile.

- The configuration setting is overridden by the NIX_PATH environment variable.

- NIX_PATH is overridden by specifying the setting as the command line flag --nix-path.

- Any current value is extended by the -I option or --extra-nix-path.

If the respective paths are accessible, the default values are:

•

$HOME/.nix-defexpr/channels

The user channel link, pointing to the current state of channels for the current user.

•

nixpkgs=$NIX_STATE_DIR/profiles/per-user/root/channels/nixpkgs

The current state of the nixpkgs channel for the root user.

•

$NIX_STATE_DIR/profiles/per-user/root/channels

The current state of all channels for the root user.

These files are set up by the Nix installer. See NIX_STATE_DIR for details on the environment variable.

Note

If restricted evaluation is enabled, the default value is empty.

If pure evaluation is enabled, builtins.nixPath always evaluates to the empty list [ ].

Default: machine-specific

•

nix-shell-always-looks-for-shell-nix

Before Nix 2.24, nix-shell would only look at shell.nix if it was in the working directory - when no file was specified.

Since Nix 2.24, nix-shell always looks for a shell.nix, whether that’s in the working directory, or in a directory that was passed as an argument.

You may set this to false to temporarily revert to the behavior of Nix 2.23 and older.

Using this setting is not recommended. It will be deprecated and removed.

Default: true

•

nix-shell-shebang-arguments-relative-to-script

Before Nix 2.24, relative file path expressions in arguments in a nix-shell shebang were resolved relative to the working directory.

Since Nix 2.24, nix-shell resolves these paths in a manner that is relative to the base directory, defined as the script’s directory.

You may set this to false to temporarily revert to the behavior of Nix 2.23 and older.

Using this setting is not recommended. It will be deprecated and removed.

Default: true

•

plugin-files

A list of plugin files to be loaded by Nix. Each of these files is dlopened by Nix. If they contain the symbol nix_plugin_entry(), this symbol is called. Alternatively, they can 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 libraries directly, as those are already available 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

•

post-build-hook

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

•

pre-build-hook

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 as sandbox-paths.

Default: empty

•

preallocate-contents

Whether to preallocate files when writing objects with known size.

Default: false

•

print-missing

Whether to print what paths need to be built or downloaded.

Default: true

•

pure-eval

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:

- builtins.currentSystem

- builtins.currentTime

- builtins.nixPath

- builtins.storePath

Default: false

•

require-drop-supplementary-groups

Following the principle of least privilege, Nix attempts 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. Search setgroups(2) for EPERM to find more detailed information on this.

If you encounter such a failure, setting this option to false enables you to ignore it and continue. But before doing so, you should consider the security implications carefully. Not dropping supplementary groups means the build sandbox is less restricted than intended.

This option defaults to true when the user is root (since root usually has permissions to call setgroups) and false otherwise.

Default: false

•

require-sigs

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 in trusted-public-keys, or a public key counterpart to a private key stored in a file listed in secret-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

•

restrict-eval

If set to true, the Nix evaluator doesn’t allow access to any files outside of builtins.nixPath, or to URIs outside of allowed-uris.

Default: false

•

run-diff-hook

If true, enable the execution of the diff-hook program.

When using the Nix daemon, run-diff-hook must be set in the nix.conf configuration file, and cannot be passed at the command line.

Default: false

•

sandbox

If set to true, builds are performed in a sandboxed environment, i.e., they’re isolated from the normal file system hierarchy and 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 the sandbox-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 to true do not run in sandboxes.

The default is true on Linux and false on all other platforms.

Default: true

Deprecated alias: build-use-chroot, build-use-sandbox

•

sandbox-build-dir

Linux only

The build directory inside the sandbox.

This directory is backed by build-dir on the host.

Default: /build

•

sandbox-dev-shm-size

Linux only

This option determines the maximum size of the tmpfs filesystem mounted on /dev/shm in Linux sandboxes. For the format, see the description of the size option of tmpfs in mount(8). The default is 50%.

Default: 50%

•

sandbox-fallback

Whether to disable sandboxing when the kernel doesn’t allow it.

Default: true

•

sandbox-paths

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 mounts 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 only be mounted in the sandbox if it exists in the host filesystem.

If the source is in the Nix store, then its closure is 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 of bash.

Default: empty

Deprecated alias: build-chroot-dirs, build-sandbox-paths

•

secret-key-files

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 to trusted-public-keys in their nix.conf.

Default: empty

•

show-trace

Whether Nix should print out a stack trace in case of Nix expression evaluation errors.

Default: false

•

ssl-cert-file

The path of a file containing CA certificates used to authenticate https:// downloads. Nix by default uses the first of the following files that exists:

1.

/etc/ssl/certs/ca-certificates.crt

2.

/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:

1.

NIX_SSL_CERT_FILE

2.

SSL_CERT_FILE

Default: machine-specific

•

stalled-download-timeout

The timeout (in seconds) for receiving data from servers during download. Nix cancels idle downloads after this timeout’s duration.

Default: 300

•

start-id

The first UID and GID to use for dynamic ID allocation.

Default: 872415232

•

store

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

•

substitute

If set to true (default), Nix uses binary substitutes if available. This option can be disabled to force building from source.

Default: true

Deprecated alias: build-use-substitutes

•

substituters

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

•

sync-before-registering

Whether to call sync() before registering a path as valid.

Default: false

•

system

The system type of the current Nix installation. Nix only builds a given store derivation locally when its system attribute equals any of the values specified here or in extra-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 the eval-system configuration option is set as the empty string.

Default: x86_64-linux

•

system-features

A set of system “features” supported by this machine.

This complements the system and extra-platforms configuration options and the corresponding system 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, see [tests/systemd-nspawn/nix][nspawn].

[nspawn]: https://github.com/NixOS/nix/blob/67bcb99700a0da1395fa063d7c6586740b304598/tests/systemd-nspawn.nix

Included by default on Linux if the auto-allocate-uids setting is enabled.

Default: machine-specific

•

tarball-ttl

The number of seconds a downloaded tarball is considered fresh. If the cached tarball is stale, Nix checks whether it is still up to date using the ETag header. Nix downloads 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, and fetchurl respect this TTL.

Default: 3600

•

timeout

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

•

trace-function-calls

If set to true, the Nix evaluator traces every function call. Nix prints 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 for flamegraph.pl.

Default: false

•

trace-import-from-derivation

By default, Nix allows Import from Derivation.

When this setting is true, Nix logs a warning indicating that it performed such an import. This option has no effect if allow-import-from-derivation is disabled.

Default: false

•

trace-verbose

Whether builtins.traceVerbose should trace its first argument when evaluated.

Default: false

•

trust-tarballs-from-git-forges

If enabled (the default), Nix considers tarballs from GitHub and similar Git forges to be locked if a Git revision is specified, e.g. github:NixOS/patchelf/7c2f768bf9601268a4e71c2ebe91e2011918a70f. This requires Nix to trust that the provider returns the correct contents for the specified Git revision.

If disabled, such tarballs are only considered locked if a narHash attribute is specified, e.g. github:NixOS/patchelf/7c2f768bf9601268a4e71c2ebe91e2011918a70f?narHash=sha256-PPXqKY2hJng4DBVE0I4xshv/vGLUskL7jl53roB8UdU%3D.

Default: true

•

trusted-public-keys

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 to false

- the store URL is configured with trusted=true

- the store object is content-addressed

Default: cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=

Deprecated alias: binary-cache-public-keys

•

trusted-substituters

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 not trusted-users) can pass as substituters only those URLs listed in trusted-substituters.

Default: empty

Deprecated alias: trusted-binary-caches

•

trusted-users

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 realisations or unsigned input-addressed store objects.

You can also specify groups by prefixing names with @. For instance, @wheel means all users in the wheel 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

•

upgrade-nix-store-path-url

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

•

use-case-hack

Whether to enable a macOS-specific hack for dealing with file name case collisions.

Default: false

•

use-cgroups

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

•

use-registries

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 in nix.conf:

```
extra-experimental-features = flakes
use-registries = ...
```

Whether to use flake registries to resolve flake references.

Default: true

•

use-sqlite-wal

Whether SQLite should use WAL mode.

Default: true

•

use-xdg-base-directories

If set to true, Nix conforms 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

•

user-agent-suffix

String appended to the user agent in HTTP requests.

Default: empty

•

warn-dirty

Whether to warn about dirty Git/Mercurial trees.

Default: true

•

warn-large-path-threshold

Warn when copying a path larger than this number of bytes to the Nix store (as determined by its NAR serialisation). Default is 0, which disables the warning. Set it to 1 to warn on all paths.

Default: 0

•

warn-short-path-literals

If set to true, the Nix evaluator will warn when encountering relative path literals that don’t start with ./ or ../.

For example, with this setting enabled, foo/bar would emit a warning suggesting to use ./foo/bar instead.

This is useful for improving code readability and making path literals more explicit.

Default: false


notmuch-hooks

package: notmuch

title: notmuch-hooks(5)

summary: hooks for notmuch

text:
# notmuch-hooks(5)

## NAME
notmuch-hooks - hooks for notmuch

## SYNOPSIS
<hook_dir>/{pre-new, post-new, post-insert}

## DESCRIPTION
Hooks are scripts (or arbitrary executables or symlinks to such) that notmuch invokes before and after certain actions. These scripts reside in a directory defined as described in notmuch-config. They must have executable permissions.

The currently available hooks are described below.

pre-new

This hook is invoked by the notmuch-new command before scanning or importing new messages into the database. If this hook exits with a non-zero status, notmuch will abort further processing of the notmuch-new command. Typically this hook is used for fetching or delivering new mail to be imported into the database.

post-new

This hook is invoked by the notmuch-new command after any new messages have been imported into the database and initial tags have been applied. The hook will not be run if there have been any errors during the scan or import. Typically this hook is used to perform additional query-based tagging on the imported messages.

post-insert

This hook is invoked by the notmuch-insert command after the message has been delivered, added to the database, and initial tags have been applied. The hook will not be run if there have been any errors during the message delivery; what is regarded as successful delivery depends on the --keep option. Typically this hook is used to perform additional query-based tagging on the delivered messages.

## SEE ALSO
notmuch, notmuch-config, notmuch-count, notmuch-dump, notmuch-insert, notmuch-new, notmuch-reply, notmuch-restore, notmuch-search, notmuch-search-terms, notmuch-show, notmuch-tag

## AUTHOR
Carl Worth and many others

## COPYRIGHT
2009-2025, Carl Worth and many others

branch: sisyphus