Linux 5.2 on a PC, we when running xmodmap. xmodmap: up to 2 keys per modifier, (keycodes in parentheses): shift lock control modl mod2 mod3 mod4 mod5 Shift_L (0x32), Shift_R (0x3e) Caps_Lock (0x42) Control_L (0x25), Control_R (0x6d) Alt_L (0x40), Alt_R (0x71) Num_Lock (0x4d) Scroll_Lock