MacOS – Execute a script with GUI Access before login

launchdmacosstartup

I need to execute a command-line tool to force maximum display brightness before user logs in (so login screen is shown with maximum brightness)

My problem is, if I run it from LaunchDaemons, it doesn't work. I think it is because from LaunchDaemons you can't run anything that interacts with the Window Server.

If I run it from LaunchAgents, it works. But it runs after login, so it is not an option.

Is there any alternative to LaunchDaemons to run scripts or programs that allow WindowServer access?

Best Answer

PreLoginAgents

macOS supports the ability to run graphical applications pre-login:

Running Agents Before Login

Most software that displays a user interface does not run prior to the user logging in. However, in some rare cases, it may be necessary to create a graphical agent that does.

By default, OS X does not allow any application to draw content prior to login. If you need to do so, your agent must call the setCanBecomeVisibleWithoutLogin: method on its windows. For more information, see the documentation for that method and the PreLoginAgents sample code.

The trick is to add the following lines to your /Library/LaunchAgents launchd plist:

<key>LimitLoadToSessionType</key>
<string>LoginWindow</string>

The executable must be stored in /Library/PrivilegedHelperTools.

We used this ability to show a notification window pre-login for Power Manager pending events.

This functionality may not be supported in the latest macOS; we have not relied on it for a long while.

Related Solutions

MacOS – Is loading your desktop before login safe

As @eyemyth said above, the script above is the equivalent of choosing "Login Window..." from menu bar when you have user switching enabled.

The only security 'issue' I can see with doing this is that momentarily your desktop will be shown until the computer calls the script - depending on how many scripts you have or how busy your login is that may not be instantly.

Also, someone (correct me if I'm wrong) could boot into single user mode, delete the plist file and then reboot - though this is an extreme.

How to write to Notification Center from a launchd command

You can send to Notification Centre using Applescript (osascript )in you shell script.

There is a very good thread here that explains the various ways of either running only Applescript as a shell script or being able to mix applescript in with bash, for example.

I created a shell script with:

#!/bin/bash
theDate=`date '+DATE: %m/%d/%y TIME:%H:%M:%S'`

osascript -e "display notification \"$theDate\" with title \"test 1\" subtitle \" sub 1\""

I then created a LaunchDaemon in the same way you have and loaded it without sudo.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>notifTest</string>
    <key>ProgramArguments</key>
    <array>
        <string>/Users/userName/Documents/notify.sh</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>StartInterval</key>
    <integer>90</integer>
</dict>
</plist>

Every 90 seconds I get a notification:

enter image description here

The notification icon you will notice is the Script Editors one. Which means the Notification is controlled by the Script Editors Notification settings in Notification Centre

Best Answer

PreLoginAgents

Running Agents Before Login

Related Solutions

MacOS – Is loading your desktop before login safe

How to write to Notification Center from a launchd command

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