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Editorial Team
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Asked: 2026-05-31T05:58:42+00:00

I built the Command Line tool (Foundation) template in Xcode. It just logs Hello

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I built the Command Line tool (Foundation) template in Xcode. It just logs “Hello World” to the console.There is only one class in it main.m. Here’s the code:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])

{

   @autoreleasepool {

       // insert code here...
       NSLog(@"Hello, World!");

   }
   return 0;

}

Now I want to run it as a daemon and log “Hello World” to the console every 10 seconds. So I moved the product/binary to /tmp on my Mac. I created the following plist for launchd:

<?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>helloDaemon</string>
    <key>ProgramArguments</key>
    <array>
        <string>/tmp/helloDaemon</string>
    </array>
    <key>StartInterval</key>
    <integer>10</integer>
</dict>
</plist>

I loaded the plist using launchctl, but I do not see any “Hello World”s in the console. Instead, I get this:

11/03/2012 00:55:35.141 com.apple.launchd: (helloDaemon) Throttling respawn: Will start in 1 seconds
11/03/2012 00:55:45.141 com.apple.launchd: (helloDaemon) Throttling respawn: Will start in 2 seconds
11/03/2012 00:55:55.140 com.apple.launchd: (helloDaemon) Throttling respawn: Will start in 3 seconds

So what’s going wrong?

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1 Answer

  1. Editorial Team

    NSLog is not working because when you launch a demon process it does not have any standard io sockets or file handles attached to it. They have to be specifically allocated. A good resource for how to create a proper daemon and how to write the console and syslog is provided in the book “Advanced Mac OS X Programming (chapter 20) by Dalrymple & Hillegass.

    They have define a skeleton program that addresses the io issues you highlight. I remembered reading it a while ago and thought that maybe someday I’d need it. The authors show a sample using the syslog.h lib using openlog() and syslog() for simple communications. They also show some other lower level methods for communication to files and even sockets (for servers, etc).

    I always appreciate when someone can tell me how to do something rather than reference something, but in this case, that is the best I can do. good luck.

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