run: add environment variable to prevent the setting of terminal title

This goes together with the existing SYSTEMD_TINT_BACKGROUND.

Closes https://github.com/systemd/systemd/issues/33301

docs/ENVIRONMENT.md

@@ -714,6 +714,10 @@ Tools using the Varlink protocol (such as `varlinkctl`) or sd-bus (such as
   no effect if the background color is explicitly selected via the relevant
   `--background=` switch of the tool.
 
+* `$SYSTEMD_ADJUST_TERMINAL_TITLE` – Takes a boolean. When false the terminal
+  window title will not be updated for interactive invocation of the mentioned
+  tools.
+
 `systemd-hostnamed`, `systemd-importd`, `systemd-localed`, `systemd-machined`,
 `systemd-portabled`, `systemd-timedated`:
 

src/run/run.c

@@ -1848,7 +1848,8 @@ static int start_transient_service(sd_bus *bus) {
                         if (!isempty(arg_background))
                                 (void) pty_forward_set_background_color(c.forward, arg_background);
 
-                        set_window_title(c.forward);
+                        if (shall_set_terminal_title())
+                                set_window_title(c.forward);
                 }
 
                 path = unit_dbus_path_from_name(service);

src/shared/ptyfwd.c

@@ -17,6 +17,7 @@
 #include "sd-event.h"
 
 #include "alloc-util.h"
+#include "env-util.h"
 #include "errno-util.h"
 #include "extract-word.h"
 #include "fd-util.h"
@@ -367,6 +368,21 @@ static int insert_background_fix(PTYForward *f, size_t offset) {
         return insert_string(f, offset, s);
 }
 
+bool shall_set_terminal_title(void) {
+        static int cache = -1;
+
+        if (cache >= 0)
+                return cache;
+
+        cache = getenv_bool("SYSTEMD_ADJUST_TERMINAL_TITLE");
+        if (cache == -ENXIO)
+                return (cache = true);
+        if (cache < 0)
+                log_debug_errno(cache, "Failed to parse $SYSTEMD_ADJUST_TERMINAL_TITLE, leaving terminal title setting enabled: %m");
+
+        return cache != 0;
+}
+
 static int insert_window_title_fix(PTYForward *f, size_t offset) {
         assert(f);
 

src/shared/ptyfwd.h

@@ -50,4 +50,6 @@ int pty_forward_set_titlef(PTYForward *f, const char *format, ...) _printf_(2,3)
 
 int pty_forward_set_title_prefix(PTYForward *f, const char *prefix);
 
+bool shall_set_terminal_title(void);
+
 DEFINE_TRIVIAL_CLEANUP_FUNC(PTYForward*, pty_forward_free);