[Bug 1822184] [NEW] clear_console locks up video when X is running and you log out from a plain text console

[Quesar]

Public bug reported:

References:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=810660
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=866898


If X is running and you switch to a plain text console (ie ctrl-alt-f3), log in as a regular user, and then log out, the display switches back to the graphical login screen and locks up.  The system is still functioning (can ssh in, etc) but the video output is frozen.

The underlying cause is:
https://gitlab.freedesktop.org/xorg/xserver/issues/492

However, the problem can at least be worked around by making
clear_console switch to tty 6 and back instead of switching to 1 and
back.  This patch corrects the problem:


--- bash-4.4.18.orig/debian/clear_console.c     2019-03-28 12:09:02.415907787 -0400
+++ bash-4.4.18/debian/clear_console.c  2019-03-28 12:08:11.984366858 -0400
@@ -205,7 +205,7 @@
 #if defined(__linux__)
   num = vtstat.v_active;
 #endif
-  tmp_num = (num == 1 ? 2 : 1);
+  tmp_num = (num == 6 ? 5 : 6);
 
   /* switch vt to clear the scrollback buffer */
   if (ioctl(fd, VT_ACTIVATE, tmp_num))

** Affects: bash (Ubuntu)
     Importance: Undecided
         Status: New

** Patch added: "makes clear_console switch to either tty6 or tty5 instead of tty1/tty2"
   https://bugs.launchpad.net/bugs/1822184/+attachment/5250280/+files/fix-clear_console-GUI-lockup.patch

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https://bugs.launchpad.net/bugs/1822184

Title:
  clear_console locks up video when X is running and you log out from a
  plain text console

Status in bash package in Ubuntu:
  New

Bug description:
  References:
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=810660
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=866898

  
  If X is running and you switch to a plain text console (ie ctrl-alt-f3), log in as a regular user, and then log out, the display switches back to the graphical login screen and locks up.  The system is still functioning (can ssh in, etc) but the video output is frozen.

  The underlying cause is:
  https://gitlab.freedesktop.org/xorg/xserver/issues/492

  However, the problem can at least be worked around by making
  clear_console switch to tty 6 and back instead of switching to 1 and
  back.  This patch corrects the problem:

  
  --- bash-4.4.18.orig/debian/clear_console.c     2019-03-28 12:09:02.415907787 -0400
  +++ bash-4.4.18/debian/clear_console.c  2019-03-28 12:08:11.984366858 -0400
  @@ -205,7 +205,7 @@
   #if defined(__linux__)
     num = vtstat.v_active;
   #endif
  -  tmp_num = (num == 1 ? 2 : 1);
  +  tmp_num = (num == 6 ? 5 : 6);
   
     /* switch vt to clear the scrollback buffer */
     if (ioctl(fd, VT_ACTIVATE, tmp_num))

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