Whats the best way to automatically start an app if its not running?

Question

I want to automatically start an application if its not running. My use is case that if I quit a particular application I want to automatically restart. Specifically in my case its the Messages app.

I always want to keep the Messages app running so if I quit Messages I want it to restart.

What's the best way to handle this?

Answer 1

What you are looking for is launchd.

It will allow you to run an app continuously (auto-start at boot, relaunch when it quits/crash)

To use it add a plist file in ~/Library/LaunchAgents/

<?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>RunAtLoad</key>  
        <true/>
        <key>KeepAlive</key>
        <true/>
        <key>Label</key>
        <string>SomeApp.restart</string>
        <key>ProgramArguments</key>
        <array>
                <string>/path/to/SomeApp.app/Contents/MacOS/SomeApp</string>
        </array>
        <key>StartCalendarInterval</key>
        <dict>
            <key>Hour</key>
            <integer>5</integer>
            <key>Minute</key>
            <integer>10</integer>
       </dict>
</dict>
</plist>

Then load it once with launchctl load ~/Library/LaunchAgents/SomeApp.restart.plist

• The RunAtLoad option will launch the application the first time launchctl runs this.
• The KeepAlive option will re-launch the application if it crashes.
• The StartCalendarInterval will run it at a certain time. Presumably this is mutually exclusive with the previous two, but is included to show what can be done with launchd Launchctl will run this after reboots.

Answer 2

As mentioned, launchctl is the command you want. I find that the syntax for launchctl to be rather difficult compared to crontab. Of course, launchctl does much more than cron. Thus, I use Lingon to provide a GUI to manage launchctl.