The cron module is a scalebox public module similar to the cron function under UNIX, which periodically sends messages to each sub-module to start related timing operations.
## Usage
Define timing operations for multiple modules through the file cron.txt.
In the cron.txt file, lines beginning with '#' are comment lines.
Each line defines the timing operation for a module, including timing operation interval definition and module name, separated by commas.
A sample cron.txt file is as follows:
```
# comments for cron.txt
@every 1m,mod0
@every 1m30s,mod1
```
The definition part of the timing operation interval refers to:
