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Now that Unity is gone, the usual way of setting a Compose Key (via Keyboard Preferences > Layout) no longer works (because in Ubuntu 18.04, Devices > Keyboard has no Layout tab).

How do we set a Compose Key in Ubuntu 18.04 Bionic Beaver?

pomsky
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Tim
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4 Answers4

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You may use (GNOME) Tweaks to set the option.

First install Tweaks by running 

sudo apt install gnome-tweaks

(or sudo apt install gnome-tweak-tool).

Alternatively, for those who prefer the GUI:

  1. launch the Ubuntu Software application.

  2. search for "gnome tweaks".

  3. install.

Then launch Tweaks and go to "Keyboard & Mouse" section. The "Compose Key" options is disabled by default. Click on the "Disabled" button.

enter image description here

Then a window will pop up. Toggle the switch at the top on and then you'll be select the compose key

enter image description here

pomsky
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    I don't have Scroll Lock, so I tried PrtScn, RightAlt, and none of them worked, what I'm missing? – Michael Sep 03 '18 at 11:02
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    Same here, I set it to Right Alt and it doesn't work. – zwolin Sep 26 '18 at 15:04
  • @zwolin Did you check out the question posted by Michael? – pomsky Sep 26 '18 at 15:11
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    @pomsky thank you, now I did. But it didn't help my case. I solved it just now by setting in GNOME Tweaks: Keyboard & Mouse -> Additional Layout Options ->Key to choose the 3rd level -> Right Alt. And now my Polish diacritic characters work as expected – zwolin Sep 26 '18 at 15:46
  • Maybe I should ask this as a separate question but is it possible to somehow set multiple compose keys (left and right alt)? It does not seem possible using the Tweaks menu. – Kvothe Nov 05 '18 at 14:36
  • @Kvothe Sorry, no idea :( Might be possible using dconf/gsettings. Asking a new question sounds like a good idea. – pomsky Nov 05 '18 at 14:43
  • @Kvothe It is possible, see my answer. – Quasímodo Oct 17 '20 at 11:28
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To expand upon what @pomsky detailed in their answer, the official documentation covers the two solutions available.

One is through installing Gnome Tweak Tool via the terminal like so: sudo apt install gnome-tweak-tool

And the other is typing the Unicode character's code point. To do this, press Ctrl+Shift+U, release all keys (you'll see an underlined u), type the code point desired, and then press Space or Enter to complete.

For example, a common one I use is referred to as “Smart Quotes” which are U+201C & U+201D respectively. So you would type 201C or 201D after releasing the initial keys, and complete the process with Space or Enter.

David Metcalfe
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Issue man xkeyboard-config and look for the compose options (shortcut: enter /compose:). You will find

compose:ralt          Right Alt                  
compose:lwin          Left Win                   
compose:lwin-altgr    3rd level of Left Win      
compose:rwin          Right Win                  
compose:rwin-altgr    3rd level of Right Win     
compose:menu          Menu                       
compose:menu-altgr    3rd level of Menu          
compose:lctrl         Left Ctrl                  
compose:lctrl-altgr   3rd level of Left Ctrl     
compose:rctrl         Right Ctrl                 
compose:rctrl-altgr   3rd level of Right Ctrl    
compose:caps          Caps Lock                  
compose:caps-altgr    3rd level of Caps Lock     
compose:102           <Less/Greater>             
compose:102-altgr     3rd level of <Less/Greater>
compose:paus          Pause                      
compose:prsc          PrtSc                      
compose:sclk          Scroll Lock

Let us say you want to pick Pause as the compose key. Just issue

setxkbmap -option compose:paus

To make it reboot-persistent, open /etc/default/keyboard with your favorite editor.

sudo nano /etc/default/keyboard

and to the line XKBOPTIONS add compose:paus. If you had other options already, separate them with commas. For example:

XKBOPTIONS="terminate:ctrl_alt_bksp,compose:paus"

Multiple compose keys can be used simultaneously.

Quasímodo
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    Always nice to have a pure CLI alternative Thanks! – Tim Oct 17 '20 at 12:43
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    @Tim You are welcome! This has an advantage of not requiring Gnome or Ubuntu or anything of the sort, only X11. – Quasímodo Oct 17 '20 at 15:11
  • setxkbmap -option compose:paus work for me

    but changing

    XKBOPTIONS="terminate:ctrl_alt_bks,compose:paus"

    In /etc/default/keyboard dont work for me :/ I don't understand.

     – 1000i100 Jul 08 '21 at 20:28
4

The dconf setting that worked for my GNOME 3.28.2 is 

/org/gnome/desktop/input-sources/xkb-options

To set the Scroll Lock as the compose key, the value should be

['compose:sclk']

See the gnome-tweaks source code for other potential values.

That means you can run a command like this:

dconf write /org/gnome/desktop/input-sources/xkb-options "['compose:sclk']"
lucidbrot
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Matthias
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    In case you would like to define multiple compose keys, simply extend the array: ['compose:prsc', 'compose:rwin']. Another way to show the list of possible keys: grep "compose:" /usr/share/X11/xkb/rules/base.lst – ph0t0nix Jul 09 '19 at 09:27
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    Eg dconf write /org/gnome/desktop/input-sources/xkb-options "['compose:sclk']" – Craig McQueen Aug 30 '19 at 03:54