diff --git a/en/optimization/debugging.txt b/en/optimization/debugging.txt
index a62810cc46b..cf4d84a1685 100644
--- a/en/optimization/debugging.txt
+++ b/en/optimization/debugging.txt
@@ -62,6 +62,11 @@ messages from MapServer.  You can pass the following values to
   environment variable always requires an absolute path since there would
   be no mapfile to make the path relative to.
 
+  Note that on Linux, if your are using a path from the `/tmp` directory
+  like `/tmp/ms_error.txt`, the log will actually output in
+  (`private directory provided by systemd <https://systemd.io/TEMPORARY_DIRECTORIES/>`__)
+  generated for the web server used (like Apache).
+
 **stderr**
   Use this to send MapServer's debug messages to the Web server's log
   file (i.e. "standard error").  If you are using Apache, your debug