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nix-super/doc/manual/src/command-ref/conf-file-prefix.md
Jan Tojnar e96faadcd6 Fix XDG_CONFIG_DIRS fallback 
According to XDG Base Directory Specification,
it should fall back to /etc/xdg when the env var is not present.
2021-11-17 14:31:15 +01:00

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Name

nix.conf - Nix configuration file

Description

By default Nix reads settings from the following places:

  • 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.

  • 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.

  • If NIX_CONFIG is set, its contents is treated as the contents of a configuration file.

The configuration files consist of name = value pairs, one per line. Other files can be included with a line like include path, where path is interpreted relative to the current conf file and a missing file is an error unless !include is used instead. Comments start with a # character. Here is an example configuration file:

keep-outputs = true       # Nice for developers
keep-derivations = true   # Idem

You can override settings on the command line using the --option flag, e.g. --option keep-outputs false. Every configuration setting also has a corresponding command line flag, e.g. --max-jobs 16; for Boolean settings, there are two flags to enable or disable the setting (e.g. --keep-failed and --no-keep-failed).

A configuration setting usually overrides any previous value. However, 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. This is also available as a command line flag (e.g. --extra-substituters).

The following settings are currently available: