What are Named Pipes or FIFO in Linux/Unix systems?

Named Pipes (also called FIFO - First-In-First-Out) are a mechanism for inter-process communication (IPC) in Linux/Unix systems that allows unrelated processes to communicate with each other. Unlike anonymous pipes, which work only between parent and child processes, named pipes create a special file on the filesystem that can be accessed by any process with appropriate permissions.

Named pipes support bidirectional communication, meaning data can flow in both directions through a single pipe, making them more versatile than regular pipes for complex communication scenarios.

Creating Named Pipes

There are two primary ways to create named pipes in Linux/Unix systems:

Using mknod() System Call

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int mknod(const char *pathname, mode_t mode, dev_t dev);

The mknod() system call creates special files including FIFOs. The parameters are:

• pathname − Path where the named pipe will be created

• mode − File type and permissions

• dev − Device information (unused for FIFOs)

Using mkfifo() Library Function

#include <sys/types.h>
#include <sys/stat.h>

int mkfifo(const char *pathname, mode_t mode);

The mkfifo() function is specifically designed for creating FIFO files and is simpler to use than mknod().

File Modes and Permissions

File types for mknod():

Permission modes:

Permissions can also be specified in octal notation (0XYZ), where X = owner, Y = group, Z = others. Values: read=4, write=2, execute=1. For example, 0640 means read+write (6) for owner, read (4) for group, no permissions (0) for others.

One-Way Communication Example

Server Process Steps:

• Creates named pipe "MYFIFO" using mknod()

• Opens the pipe in read-only mode

• Waits for messages from client

• Prints received messages until "end" is received

Client Process Steps:

• Opens the named pipe in write-only mode

• Accepts user input and sends to server

• Terminates when user enters "end"

Two-Way Communication

For bidirectional communication, both processes open the named pipe in read-write mode (O_RDWR). The server receives messages, processes them (e.g., reverses the string), and sends responses back through the same FIFO.

Advantages and Disadvantages

Conclusion

Named Pipes (FIFOs) provide a powerful IPC mechanism for unrelated processes in Linux/Unix systems. They support bidirectional communication and persist in the filesystem, making them ideal for client-server applications running in separate terminals or processes. While slower than anonymous pipes, they offer greater flexibility for inter-process communication scenarios.