# CFNetServiceMonitorStart(_:_:_:) Starts monitoring. ``` func CFNetServiceMonitorStart(_ monitor: CFNetServiceMonitor, _ recordType: CFNetServiceMonitorType, _ error: UnsafeMutablePointer?) -> Bool ``` ## Parameters `monitor` CFNetServiceMonitor, created by calling [`CFNetServiceMonitorCreate(_:_:_:_:)`](/documentation/CFNetwork/CFNetServiceMonitorCreate(_:_:_:_:)), that is to be started. `recordType` CFNetServiceMonitorType that specified the type of record to monitor. For possible values, see [`CFNetServiceMonitorType`](/documentation/CFNetwork/CFNetServiceMonitorType). `error` Pointer to a structure. If an error occurs, on output, the structure’s `domain` field will be set to the error code’s domain and the `error` field will be set to an appropriate error code. Set this parameter to `NULL` if you don’t want to receive the error code and its domain. ## Return Value `TRUE` if an asynchronous monitor was started successfully. `FALSE` if an error occurred when starting an asynchronous or synchronous monitor, or if [`CFNetServiceMonitorStop(_:_:)`](/documentation/CFNetwork/CFNetServiceMonitorStop(_:_:)) was called for an synchronous monitor. ## Discussion This function starts monitoring for changes to records of the type specified by `recordType`. If a monitor is already running for the service associated with the specified CFNetServiceMonitorRef, this function returns `FALSE`. For synchronous monitors, this function blocks until the monitor is stopped by calling [`CFNetServiceMonitorStop(_:_:)`](/documentation/CFNetwork/CFNetServiceMonitorStop(_:_:)), in which case, this function returns `FALSE`. For asynchronous monitors, this function returns `TRUE` or `FALSE`, depending on whether monitoring starts successfully. ### Special Considerations This function is thread safe. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)