A pipe in UNIX:

Question

A pipe in UNIX:

BlackTom AI · Accepted Answer

A UNIX pipe is a kernel-managed, in-memory communication channel that connects a writer to a reader, so each of the listed statements is correct.

1. Relevant concepts
- Pipe as IPC (interprocess communication): created by the pipe() system call, providing a buffered channel.
- File descriptors: UNIX processes access resources via file descriptors; pipe() returns two descriptors.
- Kernel space buffer: the pipe buffer is managed by the kernel in memory, not persisted to disk.
- Directionality: an unnamed/ordinary pipe provides a single data flow direction (one writer, one reader).

2. Step-by-step reasoning
- Option: "has input and output accessed by file descriptors"
  - The pipe() syscall returns two file descriptors: fd[0] for reading, fd[1] for writing. Thus input/output are accessed by FDs.
- Option: "runs in kernel space and operates in-memory"
  - The kernel allocates and manages the pipe buffer in kernel memory; data is copied into/out of that buffer by the kernel, so the mechanism “runs” in kernel space and operates in memory.
- Option: "is uni-directional"
  - A standard (unnamed) UNIX pipe provides a single data direction: writes go to the write end and can be read from the read end. For bidirectional communication you need two pipes or a different primitive (e.g., socketpair).
- Option: "has a read end and a write end"
  - As noted, pipe() gives distinct read and write ends (fd[0], fd[1]); attempts to read from the write end or write to the read end are incorrect usage.

3. Why the correct answer is correct
Each individual option accurately describes fundamental properties of UNIX pipes: accessed via file descriptors, kernel-managed in-memory buffers, unidirectional by default, and having distinct read/write ends. All four statements are true simultaneously.

4. Why no other options are incorrect
Because every listed option correctly states a property of UNIX pipes, there are no incorrect options among them.

Conclusion: The correct choice is "ALL are true," which matches the provided answer.

A pipe in UNIX:单项选择题

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