# os_log_create Creates a custom log object. ``` extern os_log_tos_log_create(const char *subsystem, const char *category); ``` ## Parameters `subsystem` An identifier string, in reverse DNS notation, that represents the subsystem that’s performing logging, for example, `com.your_company.your_subsystem_name`. The subsystem is used for categorization and filtering of related log messages, as well as for grouping related logging settings. `category` A category within the specified subsystem. The system uses the category to categorize and filter related log messages, as well as to group related logging settings within the subsystem’s settings. A category’s logging settings override those of the parent subsystem. ## Return Value A value of type `os_log_t`, which can be passed to other logging functions to perform logging and to determine whether a specific level of logging is enabled. A value is always returned and should be released when no longer needed. ## Discussion Typically, use the [`OS_LOG_DEFAULT`](/documentation/os/OS_LOG_DEFAULT) constant to perform logging using the system’s behavior. Create a custom log object only when you want to tag messages with a specific subsystem and category for the purpose of filtering, or to customize the logging behavior of your subsystem with a profile for debugging purposes. You only need to call this function once to initialize a custom log object. It doesn’t need to be called again when changing logging settings. The system automatically detects changes to logging settings. ## See Also [`os_log_type_enabled`](/documentation/os/OSLog/isEnabled(type:)) Returns a Boolean value that indicates whether the log can write messages with the specified log type. --- 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)