How to Create a Background Service on Mac OS X

Aug 24, 2014

 Miscellaneous

•  MAC
•  OBJECTIVE-C

As a Windows developer, I spent some time looking for an efficient way to create a service, as a counterpart of Windows service, on Mac OS X. Referring to the online documentation – Designing Daemons and Services, there are four types of background processes. The type Launch Daemon satisfies my requirements: running in the background with no access to the window server. In this article, let’s go through the process of creating a Launch Daemon on Mac OS X.

Mac Background Service: Launch Daemon

1. Launch Xcode, and create a command line application named WebTwainService.

    #import <Foundation/Foundation.h>
       
    int main(int argc, const char * argv[])
    {
       
        @autoreleasepool {
       
            // insert code here...
            NSLog(@"Hello, World!");
       
        }
       
        while (1)
        {
            sleep(100);
        }
        return 0;
    }
   

2. Build the project, and move the executable file WebTwainService to /Applications/Dynamsoft/WebTwainService.
3. Referring to Create Launch Daemons and Agents, create a configuration file com.dynamsoft.WebTwainService.plist.
   • StandardErrorPath & StandardOutPath: service log file path
   • KeepAlive. Set it true. When WebTwainService crashes unexpectedly, the system will automatically re-launch the service.
   • Label: unique value.
   • ProgramArguments: executable file path.
4. These folders are where the plist should be placed:
   • ~/Library/LaunchAgents: Per-user agents provided by the user.
   • /Library/LaunchAgents: Per-user agents provided by the administrator.
   • /Library/LaunchDaemons: System-wide daemons provided by the administrator.
   • /System/Library/LaunchAgents: Per-user agents provided by Mac OS X.
   • /System/Library/LaunchDaemons: System-wide daemons provided by Mac OS X.
5. Move com.dynamsoft.WebTwainService.plist to /Library/LaunchDaemons.
6. To register service successfully, we have to modify the file permissions. Otherwise, we’ll receive the error message: launchctl: Dubious ownership on file (skipping). Launch terminal and type in the command sudo chown root  /Library/LaunchDaemons/com.dynamsoft.WebTwainService.plist.
7. Type in sudo launchctl to run launchd:
8. Register plist with command load -D system /Library/LaunchDaemons/com.dynamsoft.WebTwainService.plist. Then we can see our service has been loaded.
9. Type in the list to check whether the service is running.
10. Now, reboot the system to verify whether the WebTwainService can work. Open /var/log/webtwain.log

Source Code

WebTwainService