man: document that user namespacing complicates file copies

diff --git a/man/systemd-nspawn.xml b/man/systemd-nspawn.xml
index 17c14e9f22d395c3247e654594ae97c563054f5c..96f8c3a61fd7d55beeeedc1bbaf5caf9c088edfd 100644 (file)
--- a/man/systemd-nspawn.xml
+++ b/man/systemd-nspawn.xml
@@ -474,7 +474,12 @@
 
         <para>Note that the picked UID/GID range is not written to <filename>/etc/passwd</filename> or
         <filename>/etc/group</filename>. In fact, the allocation of the range is not stored persistently anywhere,
-        except in the file ownership of the files and directories of the container.</para></listitem>
+        except in the file ownership of the files and directories of the container.</para>
+
+        <para>Note that when user namespacing is used file ownership on disk reflects this, and all of the container's
+        files and directories are owned by the container's effective user and group IDs. This means that copying files
+        from and to the container image requires correction of the numeric UID/GID values, according to the UID/GID
+        shift applied.</para></listitem>
       </varlistentry>
 
       <varlistentry>