Why does SaK kill gdm, which is running on a different VT?

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I run Fedora Linux 28, and have enabled sysrq. I pressed Alt+PrtScr+K, to kill a non-responsive X session. But this also restarted gdm, and one other X session, which were running on different VTs. Why?




linux gdm magic-sysrq




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    I run Fedora Linux 28, and have enabled sysrq. I pressed Alt+PrtScr+K, to kill a non-responsive X session. But this also restarted gdm, and one other X session, which were running on different VTs. Why?




    linux gdm magic-sysrq




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      up vote
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      favorite











      I run Fedora Linux 28, and have enabled sysrq. I pressed Alt+PrtScr+K, to kill a non-responsive X session. But this also restarted gdm, and one other X session, which were running on different VTs. Why?




      linux gdm magic-sysrq




      share|improve this question











      I run Fedora Linux 28, and have enabled sysrq. I pressed Alt+PrtScr+K, to kill a non-responsive X session. But this also restarted gdm, and one other X session, which were running on different VTs. Why?





      linux gdm magic-sysrq





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      asked Jun 21 at 15:48









      sourcejedi

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          1. Linux SaK kills all processes which have the current tty open.



            See https://elixir.bootlin.com/linux/v4.17/source/drivers/tty/tty_io.c#L2700




          2. systemd-logind appears to open all active ttys.



            You can verify this using lsof.



          3. When X is run as an unprivileged user and relies on systemd-logind, it does not handle a restart of systemd-logind. When X loses its connection to systemd-logind, it terminates itself.

          Alternative



          So SaK can indirectly affect all VTs, if you use unprivileged X, or Wayland.



          Instead, you can use Alt+PrtScr+R, then Ctrl+Alt+F6. You can log in on the text console, and manually kill processes e.g. Xorg, or gnome-shell if you use a GNOME Wayland session).






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            1. Linux SaK kills all processes which have the current tty open.



              See https://elixir.bootlin.com/linux/v4.17/source/drivers/tty/tty_io.c#L2700




            2. systemd-logind appears to open all active ttys.



              You can verify this using lsof.



            3. When X is run as an unprivileged user and relies on systemd-logind, it does not handle a restart of systemd-logind. When X loses its connection to systemd-logind, it terminates itself.

            Alternative



            So SaK can indirectly affect all VTs, if you use unprivileged X, or Wayland.



            Instead, you can use Alt+PrtScr+R, then Ctrl+Alt+F6. You can log in on the text console, and manually kill processes e.g. Xorg, or gnome-shell if you use a GNOME Wayland session).






            share|improve this answer



























              up vote
              1
              down vote



              accepted











              1. Linux SaK kills all processes which have the current tty open.



                See https://elixir.bootlin.com/linux/v4.17/source/drivers/tty/tty_io.c#L2700




              2. systemd-logind appears to open all active ttys.



                You can verify this using lsof.



              3. When X is run as an unprivileged user and relies on systemd-logind, it does not handle a restart of systemd-logind. When X loses its connection to systemd-logind, it terminates itself.

              Alternative



              So SaK can indirectly affect all VTs, if you use unprivileged X, or Wayland.



              Instead, you can use Alt+PrtScr+R, then Ctrl+Alt+F6. You can log in on the text console, and manually kill processes e.g. Xorg, or gnome-shell if you use a GNOME Wayland session).






              share|improve this answer

























                up vote
                1
                down vote



                accepted







                up vote
                1
                down vote



                accepted







                1. Linux SaK kills all processes which have the current tty open.



                  See https://elixir.bootlin.com/linux/v4.17/source/drivers/tty/tty_io.c#L2700




                2. systemd-logind appears to open all active ttys.



                  You can verify this using lsof.



                3. When X is run as an unprivileged user and relies on systemd-logind, it does not handle a restart of systemd-logind. When X loses its connection to systemd-logind, it terminates itself.

                Alternative



                So SaK can indirectly affect all VTs, if you use unprivileged X, or Wayland.



                Instead, you can use Alt+PrtScr+R, then Ctrl+Alt+F6. You can log in on the text console, and manually kill processes e.g. Xorg, or gnome-shell if you use a GNOME Wayland session).






                share|improve this answer
















                1. Linux SaK kills all processes which have the current tty open.



                  See https://elixir.bootlin.com/linux/v4.17/source/drivers/tty/tty_io.c#L2700




                2. systemd-logind appears to open all active ttys.



                  You can verify this using lsof.



                3. When X is run as an unprivileged user and relies on systemd-logind, it does not handle a restart of systemd-logind. When X loses its connection to systemd-logind, it terminates itself.

                Alternative



                So SaK can indirectly affect all VTs, if you use unprivileged X, or Wayland.



                Instead, you can use Alt+PrtScr+R, then Ctrl+Alt+F6. You can log in on the text console, and manually kill processes e.g. Xorg, or gnome-shell if you use a GNOME Wayland session).







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                edited Jun 21 at 15:54


























                answered Jun 21 at 15:48









                sourcejedi

                18.1k22375




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