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-rw-r--r--doc/manual/expressions/builtins.xml11
1 files changed, 10 insertions, 1 deletions
diff --git a/doc/manual/expressions/builtins.xml b/doc/manual/expressions/builtins.xml
index 5489fab0026a..54f697d852e3 100644
--- a/doc/manual/expressions/builtins.xml
+++ b/doc/manual/expressions/builtins.xml
@@ -310,8 +310,17 @@ with import (fetchTarball https://github.com/NixOS/nixpkgs-channels/archive/nixo
 
 stdenv.mkDerivation { … }
 </programlisting>
+    </para>
+
+    <para>The fetched tarball is cached for a certain amount of time
+    (1 hour by default) in <filename>~/.cache/nix/tarballs/</filename>.
+    You can change the cache timeout either on the command line with
+    <option>--option tarball-ttl <replaceable>number of seconds</replaceable></option> or
+    in the Nix configuration file with this option:
+    <literal>tarball-ttl <replaceable>number of seconds to cache</replaceable></literal>.
+    </para>
 
-    Note that when obtaining the hash with <varname>nix-prefetch-url
+    <para>Note that when obtaining the hash with <varname>nix-prefetch-url
     </varname> the option <varname>--unpack</varname> is required.
     </para>