# Modules

A module is a separate program which runs as a separate Unix process but transmits commands to fvwm to execute. Users can write their own modules to do any weird or bizarre manipulations without bloating or affecting the integrity of fvwm itself.

Modules must be spawned by fvwm so that it can set up two pipes for fvwm and the module to communicate with. The pipes are already open for the module when it starts and the file descriptors for the pipes are provided as command line arguments.

Modules can be spawned by fvwm at any time during the X session by use of the command. Modules can exist for the duration of the X session, or can perform a single task and exit. If the module is still active when fvwm is told to quit, then fvwm closes the communication pipes and waits to receive a SIGCHLD from the module, indicating that it has detected the pipe closure and has exited. If modules fail to detect the pipe closure fvwm exits after approximately 30 seconds anyway. The number of simultaneously executing modules is limited by the operating system's maximum number of simultaneously open files, usually between 60 and 256.

Modules simply transmit commands to the fvwm command engine. Commands are formatted just as in the case of a mouse binding in the `config` setup file. Certain auxiliary information is also transmitted, as in the sample module .

Please refer to the section for details.