Ubuntu不再检测外部显示器

Question

我刚刚安装了一些更新并重新启动，然后 Ubuntu 没有检测到外部显示器。它与HDMI连接。我该怎么办？它不会出现在显示设置中。我使用笔记本电脑，内置显示器正在工作并检测到，但外部显示器在今天更新后退出工作。计算机是戴尔 Latitude E7450。

$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Broadwell-U Integrated Graphics (rev 09)

~$ dmesg | grep -E 'VGA|HDMI'
[    0.882972] fb0: VESA VGA frame buffer device
[    5.718803] fb: switching to inteldrmfb from VESA VGA
[    5.719040] [drm] Replacing VGA console driver
[    6.224466] input: HDA Intel HDMI HDMI/DP,pcm=3 as /devices/pci0000:00/0000:00:03.0/sound/card0/input16
[    6.224530] input: HDA Intel HDMI HDMI/DP,pcm=7 as /devices/pci0000:00/0000:00:03.0/sound/card0/input17
[    6.224590] input: HDA Intel HDMI HDMI/DP,pcm=8 as /devices/pci0000:00/0000:00:03.0/sound/card0/input18



$ dmesg | grep -iE 'fail|error|skip'
[    0.000022] Calibrating delay loop (skipped), value calculated using timer frequency.. 5187.65 BogoMIPS (lpj=10375316)
[    3.285636] psmouse serio1: Failed to enable mouse on isa0060/serio1
[    4.077454] EXT4-fs (sda1): re-mounted. Opts: errors=remount-ro
[    5.849972] init: failsafe main process (612) killed by TERM signal
[    7.787412] systemd-logind[854]: Failed to start unit user@123.service: Unknown unit: user@123.service
[    7.787417] systemd-logind[854]: Failed to start user service: Unknown unit: user@123.service
[    8.418720] systemd-logind[854]: Failed to start unit user@125.service: Unknown unit: user@125.service
[    8.418725] systemd-logind[854]: Failed to start user service: Unknown unit: user@125.service
[    9.170491] vboxdrv: module verification failed: signature and/or  required key missing - tainting kernel
[   16.373837] systemd-logind[854]: Failed to start unit user@1000.service: Unknown unit: user@1000.service
[   16.373842] systemd-logind[854]: Failed to start user service: Unknown unit: user@1000.service

$ xrandr
Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
eDP1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 309mm x 173mm
   1920x1080      60.0*+   59.9     48.0  
   1680x1050      60.0     59.9  
   1600x1024      60.2  
   1400x1050      60.0  
   1280x1024      60.0  
   1440x900       59.9  
   1280x960       60.0  
   1360x768       59.8     60.0  
   1152x864       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

更新

以下过程解决了这个问题：从 U 盘启动 Ubuntu 14。然后重新启动到本地安装的 Ubuntu 并且外部屏幕工作。