Hi Peng Mei Yu,

I agree with Ludo' that fixing this at the package level is more 
‘appropriate’ than in the service.

Peng Mei Yu 写道：
> There is no obvious way to fix the error, so setting 
> NIX_CONF_DIR is
> easier.  Perhaps someone can fix the nix package with a clean 
> patch.
> That would be better.

Obvious is different things to different people, but here's my 
go-to approach.  Override the relevant variables during the 
install phase without changing any run-time settings:

#+begin_example
diff --git a/gnu/packages/package-management.scm 
b/gnu/packages/package-management.scm
index c1e6657dff..fefa17a162 100644
--- a/gnu/packages/package-management.scm
+++ b/gnu/packages/package-management.scm
@@ -551,6 +551,19 @@ out) and returning a package that uses that 
as its 'source'."
               (base32
                "1hbqsrp1ii2sfq8x2mahjrl2182qck76n8blrl1jfz3xq99m6i15"))))
     (build-system gnu-build-system)
+    (arguments
+     `(#:configure-flags
+       (list "--sysconfdir=/etc")
+       #:phases
+       (modify-phases %standard-phases
+         (replace 'install
+           (lambda* (#:key (make-flags '()) outputs 
#:allow-other-keys)
+             (let* ((out (assoc-ref outputs "out"))
+                    (etc (string-append out "/etc")))
+               (apply invoke "make" "install"
+                      (string-append "sysconfdir=" etc)
+                      (string-append "profiledir=" etc 
"/profile.d")
+                      make-flags)))))))
     (native-inputs `(("pkg-config" ,pkg-config)))
     (inputs `(("boost" ,boost)
               ("brotli" ,brotli)
#+end_example

It installs correctly.  I didn't test the service.

Kind regards,

T G-R