How to disable/enable/toggle touchpad in a Dell laptop

You can switch the touchpad off with this command:

xinput disable 13

Enable it back by

xinput enable 13

The device is not controlled by psmouse. It is controlled by synaptics_i2c. And it is device 13.

You can also toggle it by name as you tried before, not to depend on the ID. But if you do not connect new input devices, the ID should stay.

See this answer for some details.

To remove a wrongly detected device you need to add i8042.nopnp kernel boot parameter.

Using gsettings

If you can change settings by gsettings, generally it is the preferred option. Since you can enable/disable touchpad from System Settings, and I am pretty sure System Settings does use gsettings, it looks like the method below should do the job, on your Dell as well.

Script to toggle the touchpad

14.04

#!/usr/bin/env python3
import subprocess

key = "org.gnome.settings-daemon.peripherals.touchpad" ;val = "touchpad-enabled"
curr = subprocess.check_output(["gsettings", "get", key, val]).decode("utf-8").strip()
newval = "false" if curr == "true" else "true"
subprocess.Popen(["gsettings", "set", key, val, newval])

15.04+

#!/usr/bin/env python3
import subprocess

key = "org.gnome.desktop.peripherals.touchpad" ;val = "send-events"
curr = subprocess.check_output(["gsettings", "get", key, val]).decode("utf-8").strip()
newval = "disabled" if curr == "'enabled'" else "enabled"
subprocess.Popen(["gsettings", "set", key, val, newval])

To use it

1. Copy the script above, for your correct Ubuntu version, into an empty file, save it as toggle_touchpad.py

2. Add the following command to a shortcut:

   python3 /path/to/toggle_touchpad.py
   

   Choose: System Settings > "Keyboard" > "Shortcuts" > "Custom Shortcuts". Click the "+" and add the command:

   python3 /path/to/toggle_touchpad.py
   

Explanation

The command to disable touchpad:

for 14.04:

gsettings set org.gnome.settings-daemon.peripherals.touchpad touchpad-enabled false

for 15.04 +:

gsettings set org.gnome.desktop.peripherals.touchpad send-events disabled

Read the current state

If we use a script to read the current settings by the command:

gsettings get org.gnome.settings-daemon.peripherals.touchpad touchpad-enabled

(14.04), or

gsettings get org.gnome.desktop.peripherals.touchpad send-events

(15.04+)

We can make the script set the opposite value, and thus toggle the touchpad.

EDIT; bash version of the toggle script

Just to be complete, and because OP indicated the python script(s) worked, but not wanted to use python, the bash version(s) of the two toggle scripts:

14.04

#!/bin/bash

key="org.gnome.settings-daemon.peripherals.touchpad"
val="touchpad-enabled" ;curr="$key $val"

if [ "$(gsettings get $curr)" == "false" ]
then
 gsettings set $key $val true
else
 gsettings set $key $val false
fi

15.04+

#!/bin/bash

key="org.gnome.desktop.peripherals.touchpad"
val="send-events" ;curr="$key $val"

if [ "$(gsettings get $curr)" == "'enabled'" ]
then
 gsettings set $key $val disabled
else
 gsettings set $key $val enabled
fi

To put under a shortcut key

• Save the script as toggle_touchpad.sh

• put the following command under a custom shortcut:

  /bin/bash /path/to/toggle_touchpad.sh