man: document that sd_notify() is racy in some cases

1 files changed, 11 insertions, 4 deletions

diff --git a/man/systemd-notify.xml b/man/systemd-notify.xml
index 4a8e119eb6..9bb35a3a0c 100644
--- a/man/systemd-notify.xml
+++ b/man/systemd-notify.xml
@@ -72,10 +72,17 @@
     <para>The command line may carry a list of environment variables
     to send as part of the status update.</para>
 
-    <para>Note that systemd will refuse reception of status updates
-    from this command unless <varname>NotifyAccess=all</varname> is
-    set for the service unit this command is called from.</para>
-
+    <para>Note that systemd will refuse reception of status updates from this command unless
+    <varname>NotifyAccess=</varname> is set for the service unit this command is called from.</para>
+
+    <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
+    the sending process is still around at the time PID 1 processes the message, or if the sending process is
+    explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
+    off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
+    <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
+    <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
+    attribute the message to the unit, and thus will ignore it, even if
+    <varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
   </refsect1>
 
   <refsect1>