In finnish - Suomenkielinen versio osoitteessa iMac-Target-Display-Mode-Linuxissa

This is a step-by-step instruction for smc_util including Powerbutton support by FreekMank.

Target Display Mode is set On and Off by pressing Powerbutton.

Applicable with iMac models 2009 - 2014. Needs to have Apple High Sierra or earlier (Dual boot with Linux) in the iMac which is used as external display.

Proven to work with MiniDisplay Port cable. No personal experiences with Thunderbolt cable. Tested with iMac models 2009-2011.

The Off to work - First disable second display in your primary computer - then press Powerbutton in the display iMac.

This text is also in https://superuser.com/questions/1932625/use-imac-in-linux-as-an-external-display-in-target-display-mode/1932626#1932626

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NOTE: You may want to leave rc.local out of the installation (Step 16) - if and when you want also use the Linux OS of the display machine. (rc.local makes the machine boot directly to Target Display Mode)

Without rc.local the machine boots first to Linux OS and pressing Powerbutton sets TDM on.

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1.Download smc_util to home directory (in the intended display iMac)

git clone https://github.com/floe/smc_util.git

2.Move to smc_util

cd smc_util

3.Compile SmcDumpkey with GCC

gcc -O2 -o SmcDumpKey SmcDumpKey.c -Wall

4.Create files tdm_toggle.sh, powerbutton, powerbutton.sh and rc.local

touch tdm_toggle.sh powerbutton powerbutton.sh rc.local

5.Change content of file tdm_off.sh

#!/bin/bash
rm -f tdm_started
./SmcDumpKey MVHR 0
sleep 1
./SmcDumpKey MVMR 2
sleep 2
DISPLAY=:0.0 xrandr --output eDP --auto

6.Change content of file tdm_on.sh

#!/bin/bash
./SmcDumpKey MVHR 1
sleep 1
./SmcDumpKey MVMR 2
sleep 2
DISPLAY=:0.0 xrandr --output eDP --off
touch tdm_started

7.Create content to file tdm_toggle.sh

#!/bin/bash
pushd $(dirname "${BASH_SOURCE[0]}")

if [[ -f "tdm_started" ]]; then
  echo "Switching off TDM"
  source tdm_off.sh
else
  echo "Switch on TDM"
  source tdm_on.sh
fi

popd

8.Create content to file powerbutton

event=button/power PBTN
action=/etc/acpi/powerbutton.sh

9.Create content to file powerbutton.sh. REMEMBER TO CHANGE XXXXXXXXX to your username (in TWO LINES in the script)

#!/bin/bash

pushd $(dirname "${BASH_SOURCE[0]}")

FILE=powerbutton_pressed
NOW=$(date +%s)

if [[ -f "$FILE" ]]; then
  # Read timestamp of previous powerbutton press from file
  echo "File exists"
  typeset -i PREV=$(cat $FILE)
  echo Compare $NOW and $PREV

  # if two powerbutton presses were <1 seconds apart -> shutdown
  if [[ $(($NOW-$PREV)) -lt 2 ]]; then
    # Shutdown
    echo "Powerbutton pressed twice in a row: Shutting down"
    shutdown now
  else
    echo "Toggle TDM"
    /home/XXXXXXXXX/smc_util/tdm_toggle.sh &
  fi
else
  echo "Toggle TDM"
  /home/XXXXXXXXX/smc_util/tdm_toggle.sh &
fi

echo $NOW > $FILE

popd

10.Create content to file rc.local. REMEMBER to change XXXXXXXXX to your username

#!/bin/bash

# Start Target Display Mode such that the pc is used as external monitor right away
# Note: The Power button toggles TDM (see /etc/acpi/events)
pushd /home/XXXXXXXXX/smc_util
./tdm_on.sh
popd

11.Remove the SMC kernel driver to avoid conflicts

sudo rmmod applesmc

12.Make tdm_toggle.sh, rc.local and powerbutton.sh executable (change XXXXXXXX)

sudo chmod +x /home/XXXXXXXXX/smc_util/tdm_toggle.sh /home/XXXXXXXXX/smc_util/rc.local /home/XXXXXXXXX/smc_util/powerbutton.sh

13.Install build-essential and acpid

sudo apt install build-essential acpid acpid-suppport

14. Copy file powerbutton to /etc/acpi/events (change XXXXXXXXXX)

sudo cp /home/XXXXXXXXX/smc_util/powerbutton /etc/acpi/events

15.Copy file powerbutton.sh to /etc/acpi (change XXXXXXXX)

sudo cp /home/XXXXXXXXX/smc_util/powerbutton.sh /etc/acpi

16.Copy file rc.local to /etc (change XXXXXXXX)

sudo cp /home/XXXXXXXXX/smc_util/rc.local /etc/rc.local

17.Restart acpid

sudo systemctl restart acpid

18.Change the Powerbutton behaviour in Linux OS to

Do Nothing