StandardOutPath

StandardOutPath is a key used in launchd property lists on macOS to redirect a launched process’s standard output to a file. It is typically used together with StandardErrorPath to separately route standard error. The value of StandardOutPath is an absolute filesystem path to a file where stdout will be written for the lifetime of the job.

When a launchd job starts, its stdout is redirected to the file specified by StandardOutPath. The corresponding StandardErrorPath key controls where standard error is written. If you set StandardOutPath or StandardErrorPath to /dev/null, the respective output is discarded. The permissions of the target file and directory must allow the launchd service to write to them; otherwise the job may fail to start or the output may not be captured.

Common practice is to direct logs to files under /var/log or a dedicated log directory, with separate files for stdout and stderr to aid debugging and monitoring. Administrators should consider log rotation and disk space management to prevent unbounded growth.

Example plist snippet:

<dict>

<key>Label</key>

<string>com.example.daemon</string>

<key>ProgramArguments</key>

<array><string>/usr/bin/mydaemon</string></array>

<key>RunAtLoad</key><true/>

<key>StandardOutPath</key><string>/var/log/mydaemon.out</string>

<key>StandardErrorPath</key><string>/var/log/mydaemon.err</string>

</dict>

StandardInPath, a related key, can similarly redirect standard input. Together, these keys help manage a daemon’s I/O by isolating it from the parent process and enabling centralized logging.