Software Fn Lock

June 8, 2019

Most laptops feature a way to lock the function keys (Fn Lock), often by pressing Fn + Esc or changing some BIOS or UEFI settings.

However, my laptop (ASUS VivoBook, X510UA-BB51-CB) does not have any way to lock the function keys, forcing me to press the Fn key every time I want to, for instance, change the screen brightness or the audio volume.

Since I use those much more than the F1 to F12 keys, I had to find a software way to invert the function of those keys.

While I couldn’t come up with a perfect automatic solution, I resorted to a custom xmodmap configuration.

First, I listed the default mappings.

xmodmap -pke

My keyboard have the following mappings by default:

If not sure based on what’s written on the keyboard, you can also use the xev program to find out what is the default association.

Then, filtering the output of xmodmap -pke for those keys, I found the currently associated keycodes:

keycode  71 = F5 F5 F5 F5 F5 F5 XF86Switch_VT_5
keycode  72 = F6 F6 F6 F6 F6 F6 XF86Switch_VT_6
keycode  73 = F7 F7 F7 F7 F7 F7 XF86Switch_VT_7
keycode  76 = F10 F10 F10 F10 F10 F10 XF86Switch_VT_10
keycode  95 = F11 F11 F11 F11 F11 F11 XF86Switch_VT_11
keycode  96 = F12 F12 F12 F12 F12 F12 XF86Switch_VT_12
keycode 232 = XF86MonBrightnessDown NoSymbol XF86MonBrightnessDown
keycode 233 = XF86MonBrightnessUp NoSymbol XF86MonBrightnessUp
keycode 160 = XF86ScreenSaver NoSymbol XF86ScreenSaver
keycode 121 = XF86AudioMute NoSymbol XF86AudioMute
keycode 122 = XF86AudioLowerVolume NoSymbol XF86AudioLowerVolume
keycode 123 = XF86AudioRaiseVolume NoSymbol XF86AudioRaiseVolume

I then just have to make a ~/.xmodmaprc that inverts the keys:

keycode 71  = XF86MonBrightnessDown
keycode 232 = F5
keycode 72  = XF86MonBrightnessUp
keycode 233 = F6
keycode 73  = XF86ScreenSaver
keycode 160 = F7
keycode 76  = XF86AudioMute
keycode 121 = F10
keycode 95  = XF86AudioLowerVolume
keycode 122 = F11
keycode 96  = XF86AudioRaiseVolume
keycode 123 = F12

Make sure to add xmodmap ~/.xmodmaprc to your .xinitrc or whatever you use to configure your X11 session.