Creating FIFO's

**Dpontes11** · 11-29-2005

hi

i've been using knoppix for a few weeks because of a class at the university. this class is basically learning how to create processes in linux using C language.

the problem i'm having is the following:

im tying to use the named pipes, known as FIFO's. the thing is, when i try to create a normal unnamed pipe, it creates it and works without any problem. however, when i want to create a FIFO, it doesn't create it.

it's not a instructional error, as i've shown this problem to my teacher.

he said it might be because simply knoppix doesn't give me permitions to create this FIFO.

any sugestions on what I should do, if in fact there is something i can do?

thanx

**lakerdonald** · 11-29-2005

How are you creating this FIFO? What is the exact mkfifo invocation you're using?

**Dpontes11** · 12-02-2005

sorry about the delay... no internet acess for the last few days!

the code i'm using is:

Code:

unlink&#40;"temp_fifo"&#41;;
mknod&#40;"temp_fifo",S_IFIFO|0660,0&#41;;

when testing this last line, it returns (-1), which means that the creation on the FIFO failed.

anyway, i hope this brings new light to someone who might be able to help me out...

thanx

**lakerdonald** · 12-02-2005

Okay, include <errno.h> and <stdio.h>, then add:

Code:

perror&#40;NULL&#41;;

after the mknod() so that you can see what the exact error was.

**Dpontes11** · 12-03-2005

Ok, i'll do that.

I've been told by a friend that Knoppix really doesn't allow the creation of FIFO's, but still there could be a way...

thanks

**Dpontes11** · 12-03-2005

Ok, so this is what came up:

Code:

Operation Not Permitted

a bit generalistic, i guess...

Maybe knoppix really doens allow the creation of FIFO's.

**lakerdonald** · 12-03-2005

Are you root at the time?

**Dpontes11** · 12-04-2005

yes,i am... any suggestions yet, or are you as lost as me?

**lakerdonald** · 12-05-2005

Well according to

Code:

errno&#40;3&#41;

, "Operation not Permitted" is associated with EPERM. According to mknod(2):

Code:

 EPERM  mode requested creation of something other than a regular  file,
              FIFO  &#40;named pipe&#41;, or Unix domain socket, and the caller is not
              privileged &#40;Linux&#58; does not have the CAP_MKNOD capability&#41;; also
              returned  if the filesystem containing pathname does not support
              the type of node requested.

What kind of filesystem are you trying this on?

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