Problema com resolução no Debian 9

Question

arlecchino@arlecchino:~$ cvt 1366 768 60
# 1368x768 59.88 Hz (CVT) hsync: 47.79 kHz; pclk: 85.25 MHz
Modeline "1368x768_60.00"   85.25  1368 1440 1576 1784  768 771 781 798 -hsync +vsync
arlecchino@arlecchino:~$ xrandr --newmode "1368x768_60.00"   85.25  1368 1440 1576 1784  768 771 781 798 -hsync +vsync
xrandr: Failed to get size of gamma for output default
X Error of failed request:  BadName (named color or font does not exist)
  Major opcode of failed request:  140 (RANDR)
  Minor opcode of failed request:  16 (RRCreateMode)
  Serial number of failed request:  19
  Current serial number in output stream:  19
arlecchino@arlecchino:~$ xrandr
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 640 x 400, current 1024 x 768, maximum 1024 x 768
default connected 1024x768+0+0 0mm x 0mm
   1024x768       0.00* 
   800x600        0.00  
   640x480        0.00  
   720x400        0.00  
  1368x768_60.00 (0x27f) 85.250MHz -HSync +VSync
        h: width  1368 start 1440 end 1576 total 1784 skew    0 clock  47.79KHz
        v: height  768 start  771 end  781 total  798           clock  59.88Hz
arlecchino@arlecchino:~$ xrandr --addmode default 1368x768_60.00
xrandr: Failed to get size of gamma for output default
arlecchino@arlecchino:~$ 

Como consertar isso? eu tenho resolução máxima 1024x