Running script automatically at startup at system level

Question

Hi all,
I am a newbie with MAC. I am looking for some application that is equivalent to Window's Task Scheduler - bascially, I have a bash script and I would like it to start running at startup and be always running in the background, no matter who logs into the computer, and whoever logged in can restrat the script if needed.
Background info (if that helps understand what I am trying ot accomplish):
I am using Selenium (a UI automation tool) to automate some web testing, and my script will be calling the Selenium library to start a server to listen for requests, and it will launch browser and run tests when a request comes in.
Long story short about what I want:
I would like to automate opening up a terminal and running a bash script when my MAC starts up, and have the script always running in the background regardless of which user is currently logged in, and I would like the user to be able to stop the script and restart it if it somehow gets stuck.
I did some quick research and found out about Automator. I would like to find out/confirm if Automator is what and all I need? If not, what are my options out there?
Any suggestion and advice would be greatly appreciated! Thank you so much for reading!

Answer 1

I'm not sure whether this should be a LaunchDaemon or a LaunchAgent - if it requires user interaction as you sugest it should really be the latter, so that's what I'll show how to do.
Open TextEdit, make sure the open document is set to plain text (not rich text), copy in the following text, then save it as user.bash_script.autostart in the folder /Library/LaunchAgents/.  Then restart the machine or load the plist using launchctl in terminal.
<?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>Label</key>
          <string>user.bash_script.autostart</string>
          <key>Program</key>
          <string>/path/to/bash script</string>
          <key>KeepAlive>
          <true/>
</dict>
</plist>
This job will start the script as a daemon so that it's running for all users.  The KeepAlive key specifies that if the daemon quits launchd should automatically restart it.  It's up to you to make sure users have the correct permissions to quit the process if it gets stuck.
Note: using a LaunchAgent means that a separate instance of this process will be created for each user who logs in, and that the process will not be running if no user is logged in.  if you need to have one running instance for all users you need to use a LaunchDaemon.  However, LaunchDaemons are not supposed to have user interaction, which it seems like you want.  more details would be helpful.