Name
maerct – Ma_Sys.ma Emergency Remote Control: Kill X11 in
case of hangs.
Synopsis
maerct [-f] FILEDescription
This program has to be run by the root user. It takes a Linux
keyboard event device, e. g. /dev/input/event0 and grabs it
exclusively. Do not run it if you only have one keyboard attached.
-f forks twice.
Table of blink codes
| NumLock | CapsLock | ScrollLock | Description |
|---|---|---|---|
| slow | off | off | Program operating correctly. |
| fast | off | off | Program expecting input. |
| off | fast | off | Process X takes >80% CPU. |
| off | slow | off | RAM exceeded. |
| off | off | slow | Shorttime Load AVG greater 10. |
| off | off | fast | Command is being executed. |
| off | off | off | Program not operating. |
Table of possible inputs
| Key | Description |
|---|---|
| ESC | Cancel pending operation |
| F1 | Attempt to kill X11 process |
| F2 | Attempt to start (and immediately terminate) new X server. |
| F4 | Exit this program (no unlock required) |
| u | Press this before another operation to unlock input. |
Extended Description
This program is intended to run as a background service on an interactively used machine with a second keyboard connected for the sole purpose of being used by this program (e. g. one can install otherwise unused PS2 keyboards for the purpose).
It then outputs a limited amount of status information in form of regular blink codes using the three keyboard LEDs: NumLock, CapsLock and ScrollLock.
Apart from displaying status, it can serve as a remote control (thus the name) for killing the X-server. This might be an interesting feature for users of third-party kernel modules (e. g. NVidia drivers or VirtualBox modules) which used to cause some X11 freezes on the machine this program was developed for. By pressing [U], followed by [F1], one can cause the X-server to be terminated, freeing access to the console (if it does not work, sequence [U] followed by [F2] attempts to restart the X-server).
Be aware that similar to SysRq-codes (which may also work in such cases), this program allows bypassing any running screensaver! In case you only want the keyboard blinking, consider using ma_capsblinker(11) (currently does not provide any status information, but does not need to run on a separate keyboard).
This program is provided together with an LSB init script
(masysma-emergency-remote-control) and a default
configuration in /etc/default/maerct which is actually a
shellscript sourced into the init script, allowing for host-specific
configuration or any other logic.
Compilation
To compile this program, a C compiler is needed e. g. as provided by
Debian package gcc-8-base. Additionally, the
ant build tool is needed and can then be invoked by running
ant. To build the Debian package (with the necessary
dependencies installed), use ant package.