I have been using Ubuntu 17.10 for a while and is working great. But today after the update, I have a new shortcut, Alt+Shift, as an alternative Switch to the next input source. Alt+Shift is a common modifier in Intellij so a lot of shortcuts doesn't work any more.
I tried to change the shortcut but it is not listed in the shortcuts window.
Is there a file where I can change it (the alternative)?
Here is the screenshot of the option
Finally I found the option. I had to install Tweaks and go to
Keyboard and mouse > Additional layout options > switching to another layout
The strange thing is that there is that the default shortcut super+space was not selected in that window, only the alternative shortcut.
In my answer I assume that you use Gnome 3.x.
You can use Tweaks, but you can also write the value directly, for example, changing from Alt+Shift to Ctrl+Shift can be done by the following command in terminal:
To disable the option of alternative switch to the next source type in terminal:
This worked for me. No reboot is necessary.
For Ubuntu 18.04: Alternative switch to next source Can Changed or Disabled only with "Tweak Tool":
and then Keyboard & Mouse > Additional Layout Options > Switching to another layout