Launching Custom Daemons Using launchd

In OSX I needed a shell script to execute at login. There are a few different ways to perform this so I thought it might be helpful to document what your options are. This is the shell script I will execute:

#!/bin/bash

function start() {
    echo ${PATH}
    echo "start mkdocs"
    # It should not append a & symbol to the end as urual to run the command in the background, cause we will let launch to take over the task.
    /Library/Frameworks/Python.framework/Versions/3.10/bin/mkdocs serve 

}

function stop() {
    echo "stop mkdocs client..."
  ps -ef | grep "mkdocs" | awk  '{ print $2 }' | xargs  kill 
}

case ${1} in
  "start")
    start
  ;;
  "stop")
    stop    
  ;;
  "restart")
    stop
    sleep 3
    start
  ;;
  "")
    start   
  ;;

  *)
  echo "error arguents"
  exit 1
  ;;
esac

This script was named "blogserver.sh" locating in my blog diractory "\~/wk/blog/". It start my blogserver, so that I can browse my blogs located in my own cumputer in the browser. It should be noted that the services programe you are going to excute should not append a & symbol to the end as urual to daemonize , cause we will let launchd to take over the task. If you do this way, launchd will lose track of it and attempt to relaunch it.

The interface to launchd is a tool called launchctl which allows for loading and unloading daemons into launchd. XML formatted plist files are used to describe operations loaded into launchctl.

<?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>mkdocs.blogs</string>
    <key>ProgramArguments</key>
    <array>
      <string>./blogserver.sh</string>
      <string>start</string>
    </array>
    <key>WorkingDirectory</key>
    <string>/Users/wzq/wk/blog</string>
    <key>RunAtLoad</key>
    <true />
    <key>StandardErrorPath</key>
    <string>/Users/wzq/Library/Logs/myblogs.log</string>
    <key>StandardOutPath</key>
    <string>/Users/wzq/Library/Logs/myblogs.log</string>
  </dict>
</plist>

The above file mkdocs.blogs.plist needs to be saved in the ~/Library/LaunchAgents directory. As you can see the xml dictates that the "blogserver.sh" file should be executed at load, note we no longer need a ".command" file extension. We will now use launchctl to load our plist file.

 launchctl load ~/Library/LaunchAgents/mkdocs.blogs.plist

To verify that your script executed correctly lets ask launchctl to show us what is running.

launchctl list | grep "mkdocs.blogs"

You will likely see an entries with three columns. Mine looks like this:

758 0   mkdocs.blogs

The first column is the process id. The second column displays the last exit status of the job, zero represent success.

Property list

A list of often used keys follows below. All keys are optional unless otherwise noted. For a full list, see Apple's manpage for launchd.plist.

Reference

• https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLaunchdJobs.html##//apple_ref/doc/uid/10000172i-SW7-BCIEDDBJ

• https://en.wikipedia.org/wiki/Launchd

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