Question

I created and written to a named pipe in C under Linux. For how long the text that is written in there is saved in the named pipe?

From what I have done, and the bytes of the pipe file after my program is run I suppose that the text is not preserved in the pipe after the program ends. In the mkfifo manual there is no info about this. I know that ordinary pipes are destroyed after the process that have created them is closed. But what about named pipes, that are still in your file system after the program has finished?

This is the code I use to create a named pipe and to write/read from it.

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

int main(int argc, char *argv[]) {
    int FIFOFileDescriptorID;
    FIFOFileDescriptorID = mkfifo(argv[1], 0660);

    int ProccesID = fork();
    if (ProccesID == 0) {
        int TempFileDescriptor = 0;
        char buffer[512] = "Some random text goes here...";

        TempFileDescriptor = open(argv[1], O_WRONLY);
        write(TempFileDescriptor, &buffer, sizeof(buffer));
        close(TempFileDescriptor);
    } else {
        int TempFileDescriptor = 0;
        char buffer[512];

        TempFileDescriptor = open(argv[1], O_RDONLY);
        read(TempFileDescriptor, &buffer, sizeof(buffer));
        close(TempFileDescriptor);
        printf("Received string: %s\n", buffer);
    }

    return 0;
}

After I have run this program and created and use the pipe for write/read, I run another one – just to read the text from the given pipe. Indeed, there was no text there.

I will exam this thing better, because there is a good change, after I start the program do delete/create the pipe again.

Answer 1

It’ll not save anything. When you read/write something to the named pipe, it the process will be blocked unless some other process writes/reads from the same named pipe.

The file stays in the file-system. But the content goes away when reading/writing finishes.

From linux manual,

Once you have created a FIFO special file in this way, any process
can open it for reading or writing, in the same way as an ordinary file.
However, it has to be open at both ends simultaneously before you can
proceed to do any input or output operations on it. Opening a FIFO for
reading normally blocks until some other process opens the same FIFO for
writing, and vice versa.