YJL

Back in December, 2008, I posted Proper way to turn on SHMConfig in X Server 1.5 with input hotplugging, that was when HAL had not been deprecated. I checked my un-merging log, HAL was removed from my system in December, 2010, two years later of the post.

According to man synaptics, since X server 1.6, you don't need SHMConfig for changing settings on the fly via synclient. However, the -m touchpad activity monitoring option still requires SHMConfig, or you will get the same old error message:

Can't access shared memory area. SHMConfig disabled?

I have a plan for monitoring activity of touchpad, so I tried to turn it on again and the proper way is to edit /usr/share/X11/xorg.conf.d/50-synaptics.conf:

Section "InputClass"
        Identifier "touchpad catchall"
        Driver "synaptics"
        MatchDevicePath "/dev/input/event*"
        MatchIsTouchpad "on"
        Option "SHMConfig" "on"
EndSection

The lines in bold text were what I added to it, the rest were the original content. I found out /dev/input/event* is crucial to get SHMConfig turned on. Without it, I still got the same error message saying SHMConfig disabled. I don't know if it also affects other options, but you don't actually need to put touchpad options here, you can change in your ~/.xinitrc or write a startup script.

If you don't have the file, then just create one in the same directory or one listed in man xorg.conf, X server looks into many different directories for configuration files.

Your X probably doesn't have xorg.conf but automatically detect devices. Since Fedora 9, there is no xorg.conf after installing.

I just want to turn on the SHMConfig in order to change some settings of Synaptics touchpad. I then found out I need to create a configuration file, but the fact is not necessary. I only need to add a setting to /usr/share/hal/fdi/policy/20thirdparty/10-synaptics.fdi:

<?xml version="1.0" encoding="ISO-8859-1"?>
<deviceinfo version="0.2">
  <device>
    <match key="info.capabilities" contains="input.touchpad">
      <match key="info.product" contains="Synaptics TouchPad">
    <merge key="input.x11_driver" type="string">synaptics</merge>
    <merge key="input.x11_options.SHMConfig" type="string">on</merge>
      </match>
      <match key="info.product" contains="AlpsPS/2 ALPS">
    <merge key="input.x11_driver" type="string">synaptics</merge>
      </match>
      <match key="info.product" contains="appletouch">
          <merge key="input.x11_driver" type="string">synaptics</merge>
      </match>
      <match key="info.product" contains="bcm5974">
          <merge key="input.x11_driver" type="string">synaptics</merge>
      </match>
    </match>
  </device>
</deviceinfo>

This file ships with Fedora 10 with an added line:

<merge key="input.x11_options.SHMConfig" type="string">on</merge>

That will enable SHMConfig after your restart X.

By the way, if you want to auto-disable the touchpad while external mouse attached, add a /etc/udev/rules.d/50-synaptics.rules with content as follows:

ACTION=="add", SUBSYSTEM=="input", ID_CLASS="mouse", RUN+="/usr/bin/synclient -s TouchpadOff=1"
ACTION=="remove", SUBSYSTEM=="input", ID_CLASS="mouse", RUN+="/usr/bin/synclient -s TouchpadOff=0"

You should see the touchpad being disabled/enabled if you plug/unplug a mouse without restart X.

You can read more about touchpad and input hotplugging on ArchWiki.

Updated on 2009-10-26: Added -s to synclient command, newer version requires specifying the use of SHM. Without that argument, the root account (or whom run the synclient) couldn't be able to set the touchpad's parameters.