man: document that ConditionKernelCommandLine= looks at /proc/1/environ in containers

Fixes: #16941
(cherry picked from commit af4b8f8048e2d2da0b1a1a4927339cf39c62fb8a)

diff --git a/man/systemd.unit.xml b/man/systemd.unit.xml
index 214c688160c5254d54ffb736e30bb07fd5fdcedb..cf6af676a47f80a9f7fc26684c468e672bf132fd 100644 (file)
--- a/man/systemd.unit.xml
+++ b/man/systemd.unit.xml
@@ -1209,7 +1209,10 @@
           argument must either be a single word, or an assignment (i.e. two words, separated by
           <literal>=</literal>). In the former case the kernel command line is searched for the word
           appearing as is, or as left hand side of an assignment. In the latter case, the exact assignment is
-          looked for with right and left hand side matching.</para>
+          looked for with right and left hand side matching. This operates on the kernel command line
+          communicated to userspace via <filename>/proc/cmdline</filename>, except when the service manager
+          is invoked as payload of a container manager, in which case the command line of <filename>PID
+          1</filename> is used instead (i.e. <filename>/proc/1/cmdline</filename>).</para>
           </listitem>
         </varlistentry>