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-rw-r--r--doc/manual/src/command-ref/conf-file-prefix.md30
1 files changed, 22 insertions, 8 deletions
diff --git a/doc/manual/src/command-ref/conf-file-prefix.md b/doc/manual/src/command-ref/conf-file-prefix.md
index 9987393d2..3140170ab 100644
--- a/doc/manual/src/command-ref/conf-file-prefix.md
+++ b/doc/manual/src/command-ref/conf-file-prefix.md
@@ -19,19 +19,33 @@ By default Nix reads settings from the following places:
and `XDG_CONFIG_HOME`. If these are unset, it will look in
`$HOME/.config/nix.conf`.
-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
+ - 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`.
+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: