[opensuse-factory] Solved - Re: Start displaymanager only if monitor is connected

3 Dec 2018

      On Mon, 3 Dec 2018 at 13:23, Manvendra Bhangui  wrote:
...
So I was thinking of a way the boot process can boot in runlevel 3 if
monitor is not switched on. I found a way to detect this by installing
the application monitor-get-edid.
So finally I did it. With a bit of google search, I stumbled on this
post which was about running a script when monitor gets connected.
The command
cat /sys/class/drm/card0-HDMI-A-1/status
gives you the status of the connection of the monitor.

https://superuser.com/questions/278082/linux-how-to-run-a-script-when-an-ext...

So my final solution is a systemd service, a shell script and a udev rule

1) systemd service
$ cat /usr/lib/systemd/system/monitor-check.service
[Unit]
Description=Monitor Hotplug
Before=display-manager.service

[Service]
Type=simple
RemainAfterExit=no
ExecStart=/home/mbhangui/bin/monitor_plug.sh

[Install]
WantedBy=graphical.target

2) A shell script to put the system in runlevel 3 or runlevel 5
depending on if the monitor is connected
$ cat monitor_plug.sh
#!/bin/sh
file=/etc/sysconfig/displaymanager
uid=$(id -u mbhangui)
#/usr/sbin/monitor-get-edid >/dev/null 2>&1

prev_state=$(cat /run/user/$uid/monitor_status 2>/dev/null)
cur_state=$(cat /sys/class/drm/card0-HDMI-A-1/status 2>/dev/null)

connect()
{
        if [ "$cur_state" != "$prev_state" ] ; then
                sed -i
's}.*DISPLAYMANAGER_AUTOLOGIN=.*}DISPLAYMANAGER_AUTOLOGIN="mbhangui"}g'
$file
                if [ ! -d /run/user/$uid ] ; then
                        exit 0
                fi
                echo $cur_state > /run/user/$uid/monitor_status
                systemctl is-active --quiet display-manager.service
                if [ $? -ne 0 ] ; then
                        systemctl isolate graphical.target
                fi
        fi
}

disconnect()
{
        if [ ! "$cur_state" = "$prev_state" ] ; then
                sed -i
's}.*DISPLAYMANAGER_AUTOLOGIN=.*}#DISPLAYMANAGER_AUTOLOGIN="mbhangui"}g'
$file
                if [ ! -d /run/user/$uid ] ; then
                        systemctl isolate multi-user.target
                        exit 0
                fi
                echo $cur_state > /run/user/$uid/monitor_status
                systemctl is-active --quiet display-manager.service
                if [ $? -eq 0 ] ; then
                        systemctl isolate multi-user.target
                fi
        fi
}
if [ $(cat /sys/class/drm/card0-HDMI-A-1/status) == "connected" ] ; then
        connect
elif [ $(cat /sys/class/drm/card0-HDMI-A-1/status) == "disconnected" ] ; then
        disconnect
else
        exit 0
fi

3) udev rule in /etc/udev/rules.d/55-monitor.rules
ACTION=="change" KERNEL=="card0", SUBSYSTEM=="drm",
RUN+="/usr/bin/systemctl start monitor-check.service"
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