What does the 'error write epipe undefined' message signify?

The 'error write epipe undefined' message typically indicates a problem with the `epipe` system call in a program, specifically related to writing to a shared memory region. `epipe` (efficient pipe) is used for inter-process communication (IPC). The 'undefined' part suggests that either the `epipe` call itself is not defined in the program's environment (perhaps due to an incorrect compilation or missing library) or that the system is unable to find a valid `epipe` implementation. It often arises when using shared memory for fast data exchange between processes and a necessary system component or library is not linked correctly.