xstartup: Require sess dsktop file if WM specified

xinitrc is poorly or not at all supported on modern Un*x distributions.
Executing it as a fallback if the session desktop file for the specified
window manager could not be found sometimes caused hard-to-diagnose
issues.

ChangeLog.md

@@ -69,6 +69,10 @@ with the TurboVNC Server on Ubuntu 23.10 and later (if the `polkitd-pkla`
 package is not installed) and on RHEL 7 and Fedora 19 and later (if the
 `polkit-pkla-compat` package is not installed.)
 
+12. The default X startup script (`xstartup.turbovnc`) now throws an error,
+rather than trying to execute **xinitrc** or twm, if a window manager is
+specified and the session desktop file for the window manager cannot be found.
+
 
 3.0.3
 =====

unix/vncserver.man.in

@@ -136,13 +136,13 @@ another command to launch the window manager.
 .TP
 \fB-wm\fR \fIwindow-manager\fR
 This sets the value of the \fBTVNC_WM\fR environment variable to
-\fIwindow-manager\fR. The default X startup script will launch the window
-manager specified in the \fBTVNC_WM\fR environment variable, if it is set and a
+\fIwindow-manager\fR. If the \fBTVNC_WM\fR environment variable is set, then
+the default X startup script will launch the specified window manager if a
 corresponding session desktop file exists under \fB/usr/share/xsessions\fR
-(\fB/usr/local/share/xsessions\fR on *BSD systems.) If the window manager is
-not specified, then the default X startup script will launch the "gnome" or
-"ubuntu" window manager if a corresponding session desktop file exists and
-execute \fB/etc/X11/xinit/xinitrc\fR otherwise.
+(\fB/usr/local/share/xsessions\fR on *BSD systems) and fail otherwise. If the
+window manager is not specified, then the default X startup script will launch
+the "gnome" or "ubuntu" window manager if a corresponding session desktop file
+exists and execute \fB/etc/X11/xinit/xinitrc\fR otherwise.
 .TP
 \fB\-x509cert\fR \fIcert\fR
 Specify the X.509 signed certificate file (in PEM format) to use with X.509

unix/xstartup.turbovnc

@@ -82,6 +82,31 @@ OS=`uname -s`
 
 # Emulate GDM
 
+find_session()
+{
+ for SESSION in $SESSIONS; do
+ if [ "$XSESSIONSDIR" != "" -a -f $XSESSIONSDIR/$SESSION.desktop ]; then
+ DESKTOP_SESSION=$SESSION; export DESKTOP_SESSION
+ fi
+ done
+ if [ "$DESKTOP_SESSION" = "" ]; then
+ if [ "$TVNC_WM" = "" ]; then
+ echo "xstartup.turbovnc: The session desktop file for the default window manager was"
+ echo "xstartup.turbovnc: not found at:"
+ else
+ echo "xstartup.turbovnc: The session desktop file for the '$TVNC_WM'"
+ echo "xstartup.turbovnc: window manager was not found at:"
+ fi
+ for SESSION in $SESSIONS; do
+ echo "xstartup.turbovnc: $XSESSIONSDIR/$SESSION.desktop"
+ done
+ if [ "$TVNC_WM" != "" ]; then
+ exit 1
+ fi
+ fi
+ unset SESSIONS
+}
+
 # Use Unity 2D on Ubuntu 12 if no WM is specified. Historically, Unity 3D
 # 5.20.x didn't even pretend to work properly with our X server, although it
 # probably would now.
@@ -113,16 +138,12 @@ case "$TVNC_WM" in
  NOXSESSION=1
  TVNC_WM=`echo $TVNC_WM | $SED -r 's/:noxsession$//g'`
  fi
- # RHEL 7, Fedora: gnome-classic
+ # RHEL 7+, Fedora: gnome-classic
  # Ubuntu 12: ubuntu-2d
  # Ubuntu 14: gnome-fallback
  # Ubuntu 16+: gnome-flashback-metacity
- for SESSION in "gnome-classic" "gnome-fallback" "ubuntu-2d" "2d-gnome" \
- "gnome-flashback-metacity"; do
- if [ "$XSESSIONSDIR" != "" -a -f $XSESSIONSDIR/$SESSION.desktop ]; then
- DESKTOP_SESSION=$SESSION; export DESKTOP_SESSION
- fi
- done
+ SESSIONS="gnome-classic gnome-fallback ubuntu-2d 2d-gnome gnome-flashback-metacity"
+ find_session
  unset TVNC_WM
  ;;
  *)
@@ -136,22 +157,16 @@ case "$TVNC_WM" in
  esac
  if [ "$TVNC_WM" = "" ]; then
  # No window manager was specified. Use GNOME or Unity if it exists.
- for SESSION in "gnome" "ubuntu"; do
- if [ "$XSESSIONSDIR" != "" -a -f $XSESSIONSDIR/$SESSION.desktop ]; then
- DESKTOP_SESSION=$SESSION; export DESKTOP_SESSION
- fi
- done
+ SESSIONS="gnome ubuntu"
+ find_session
  else
  # For backward compatibility with TurboVNC 2.2.x, we allow a window
  # manager's startup script (e.g. mate-session, gnome-session) to be
  # specified using -wm / $wm, but if there is a matching session desktop
  # file for it, we use that instead.
- SESSION=`echo $TVNC_WM | $SED -r 's/^.*\/|-session$//g'`
- if [ "$XSESSIONSDIR" != "" -a -f "$XSESSIONSDIR/$SESSION.desktop" ]; then
- DESKTOP_SESSION=$SESSION; export DESKTOP_SESSION
- unset TVNC_WM
- fi
- unset SESSION
+ SESSIONS="`echo $TVNC_WM | $SED -r 's/^.*\/|-session$//g'`"
+ find_session
+ unset TVNC_WM
  fi
  ;;
 esac