How to disable a laptop touchpad on Linux

Or any input device for that matter. Install xinput:

sudo apt-get install xinput

xinput list

⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ Logitech USB-PS/2 Optical Mouse id=11 [slave pointer (2)]
⎜ ↳ AlpsPS/2 ALPS DualPoint TouchPad id=14 [slave pointer (2)]
⎜ ↳ AlpsPS/2 ALPS DualPoint Stick id=15 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Video Bus id=7 [slave keyboard (3)]
↳ Power Button id=8 [slave keyboard (3)]
↳ Sleep Button id=9 [slave keyboard (3)]
↳ Laptop_Integrated_Webcam_FHD: I id=10 [slave keyboard (3)]
↳ Dell WMI hotkeys id=12 [slave keyboard (3)]
↳ AT Translated Set 2 keyboard id=13 [slave keyboard (3)]

Touch pad ID is 14

xinput set-prop 14 "Device Enabled" 0