man: document that scope units can fail, but not due to process exit statusses

Let's clarify that scope units can fail, but not due to process exit
statusses.

This hopefully clears up some confusion that manifested in #14142: scope
units can fail, but for other reasons than assumed there.

Fixes: #14142

diff --git a/man/systemd.scope.xml b/man/systemd.scope.xml
index daf3554db2b663b457e93acd576c2188d2eb3417..e4de2b0fd0db43dbdd742162aabe076e60d3c183 100644 (file)
--- a/man/systemd.scope.xml
+++ b/man/systemd.scope.xml
@@ -45,6 +45,15 @@
     url="https://www.freedesktop.org/wiki/Software/systemd/ControlGroupInterface/">New
     Control Group Interfaces</ulink> for an introduction on how to make
     use of scope units from programs.</para>
+
+    <para>Note that unlike service units scope units have no "main" process, all processes in the scope are
+    equivalent. The lifecycle of the scope unit is thus not bound to the lifetime of one specific process but
+    to the existance of any processes in the scope. This also means that the exit status of these processes
+    do not cause the scope unit to enter a failure state. Scope units may still enter a failure state, for
+    example due to resource exhaustion or stop timeouts being reached, but not due to programs inside of them
+    terminating uncleanly. Since processes managed as scope units generally remain children of the original
+    process that forked them off it's also the job of that process to collect their exit statuses and act on
+    them as needed.</para>
   </refsect1>
 
   <refsect1>