man: encourage the creation of empty machine-id instead of deleting it

Current text hints that machine-id in template image should be empty
if the system is read-only. But most of the bare metal systems and
regular VMs have /etc read-only at this phase of boot.

(cherry picked from commit 64fcb07199f8409a074575eda5abb69b0caab06f)

diff --git a/man/machine-id.xml b/man/machine-id.xml
index 79e020768d0edd1a7faf17e0577d3fadc88e328f..14ba878677c7c8b6997053c70e987cb6134b3c58 100644 (file)
--- a/man/machine-id.xml
+++ b/man/machine-id.xml
@@ -84,9 +84,9 @@
     containers or in the cloud, <filename>/etc/machine-id</filename> should be either missing or an empty
     file in the generic file system image (the difference between the two options is described under "First
     Boot Semantics" below). An ID will be generated during boot and saved to this file if possible. Having an
-    empty file in place is useful because it allows a temporary file to be bind-mounted over the real file,
-    in case the image is used read-only. Also see <ulink url="https://systemd.io/BUILDING_IMAGES">Safely
-    Building Images</ulink>.</para>
+    empty file in place is recommended because it allows a temporary file to be bind-mounted over the real file,
+    in case the image is used read-only and when <filename>/etc</filename> is mounted read-only in the early boot.
+    Also see <ulink url="https://systemd.io/BUILDING_IMAGES">Safely Building Images</ulink>.</para>
 
     <para><citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
     may be used to initialize <filename>/etc/machine-id</filename> on mounted (but not