My mini-PC has Intel i7 running Lubuntu-18.04.
It has 2 monitor outputs, one HDMI and one DisplayPort.
The HDMI port has a HDMI monitor (E2441) plugged into it.
The DisplayPort has a DisplayPort-HDMI converter in it, with a big HDMI TV screen plugged into it, and switched on.
But Menu > Preferences > Monitor Settings (lxrandr) only shows 1 monitor attached.
/var/log/syslog shows:
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011ports:
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011hdmi-output-1: HDMI / DisplayPort 2 (priority 5800, latency offset 0 usec, available: yes)
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011properties:
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011#011device.icon_name = "video-display"
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011#011device.product.name = "E2441"
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011active port: <hdmi-output-1>
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: 2 source(s) available.
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011properties:
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011hdmi-output-0: HDMI / DisplayPort (priority 5900, latency offset 0 usec, available: no)
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011properties:
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011#011device.icon_name = "video-display"
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011hdmi-output-1: HDMI / DisplayPort 2 (priority 5800, latency offset 0 usec, available: yes)
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011properties:
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011#011device.icon_name = "video-display"
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011#011device.product.name = "E2441"
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011hdmi-output-2: HDMI / DisplayPort 3 (priority 5700, latency offset 0 usec, available: no)
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011properties:
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011#011device.icon_name = "video-display"
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011hdmi-output-3: HDMI / DisplayPort 4 (priority 5600, latency offset 0 usec, available: no)
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011properties:
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011#011device.icon_name = "video-display"
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011hdmi-output-4: HDMI / DisplayPort 5 (priority 5500, latency offset 0 usec, available: no)
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011properties:
Oct 17 07:56:06 i7 pulseaudio[2107]: [pulseaudio] main.c: #011#011#011#011device.icon_name = "video-display"
The "available: no" seems to be the problem.
Does it need a special driver?
$ xrandr
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
DP-1 disconnected primary (normal left inverted right x axis y axis)
HDMI-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 531mm x 299mm
1920x1080 60.00*+ 50.00 59.94
1920x1080i 60.00 50.00 59.94
1680x1050 59.88
1280x1024 75.02 60.02
1280x960 60.00
1152x864 75.00
1280x720 60.00 50.00 59.94
1024x768 75.03 60.00
832x624 74.55
800x600 75.00 60.32 56.25
720x576 50.00
720x480 60.00 59.94
640x480 75.00 60.00 59.94
720x400 70.08
$ uname -a
Linux i7 4.15.0-65-generic #74-Ubuntu SMP Tue Sep 17 17:06:04 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
This says it will load all HWE modules:
https://wiki.ubuntu.com/Kernel/LTSEnablementStack#Ubuntu_14.04_LTS_-_Trusty_Tahr says for Bionic:
$ sudo apt-get install --install-recommends linux-generic-hwe-18.04 xserver-xorg-hwe-18.04
I tried it, followed by a reboot - but still no change, apart from:
$ uname -a
Linux i7 5.0.0-31-generic #33~18.04.1-Ubuntu SMP Tue Oct 1 10:20:39 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
External monitor not detected on Ubuntu 18.04 is a similar problem with different hardware.
It seems to show that nobody agrees what fixes it.
What next?
I don't know what any of this means, but maybe somebody does.
$ sudo lshw -c video
name: i915
$ modinfo i915
filename: /lib/modules/5.0.0-32-generic/kernel/drivers/gpu/drm/i915/i915.ko
license: GPL and additional rights
description: Intel Graphics
author: Intel Corporation
...
parm: enable_dp_mst:Enable multi-stream transport (MST) for new DisplayPort sinks. (default: true) (bool)
parm: enable_dpcd_backlight:Enable support for DPCD backlight control (default:false) (bool)
parm: enable_gvt:Enable support for Intel GVT-g graphics virtualization host support(default:false) (bool)
(full listing at https://davekimble.net/problem.DP.txt)
/sys/class/drm/card0/card0-DP-1/status = "disconnected"
/sys/class/drm/card0/card0-HDMI-A-1/status = "connected"
TL;DR Check if your DP cable firmly plugged in
As mine wasn't fully plugged in, so I had "no signal" message on my monitor. After I inserted the cable firmly I got the signal.
Before, I've tried to install mesa drivers and wake up DP manually with
xrandr -d :0 --output DP-1 --auto
Eventually I removed all installed packages and it's working okay on blank Ubuntu 20.04.
Does your miniPC have a DP++ icon? (see chapter "DisplayPort dual-mode" on DisplayPort wikipedia page) Laptops had it from the beginning, but first GPUs with DP needed active DP-HDMI adapters (which start at 20-30$). If you have access to DP cable and monitor, try it that way to check the port is working.
Maybe you could add info about your miniPC. I assume you are runnign from Intel IGP, but which gen?