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ACER ASPIRE 5738 (ZG) TOUCHPAD ENABLE/DISABLE BUTTON ISSUE
                Written on 20.11.2011
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Problem description

Acer Aspire 5738 has a button next to the touchpad that allows toggling the
touchpad on or off. Unfortunately for some reason this doesn't work really
well in Linux distributions by default. If you disable the touchpad and then
try re-enabling it, nothing will happen.


Solution

Open your GRUB configuration file (grub/menu.lst) and add the parameter
"i8042.nomux" to your kernel settings. Example:

    # (0) Arch Linux
    title   Arch Linux
    root    (hd0,0)
    kernel  /vmlinuz-linux root=/dev/disk/by-uuid/... ro i8042.nomux
    initrd  /initframfs-linux.img



Source
https://bugs.launchpad.net/ubuntu/+source/xfree86-driver-synaptics/+bug/374459/comments/68