Question

I am writing a simple C program to exchange messages
through named pipes on linux. The problem is I have
to run it as superuser to make it work, otherwise i get:
“Permission denied” error.
Write permission on the directory is granted:

drwxr-xr-x 2 alpa alpa  4096 26 giu 17.24 .

Umask should be ok:

$ umask
0022

The pipe file is actually created, but with wrong permissions bits:

$ ls -l | grep fifo.fifo
pr----x--t 1 alpa alpa     0 26 giu 17.29 fifo.fifo

So when I try to open it for reading or writing the
open() system call fails.

Here is the code:

...
if(mkfifo(pathname, perms) == -1 && errno != EEXIST)
  return NULL;
if(chmod(pathname, perms) == -1)
    return NULL;
...
fifo->fd[0]= open(fifo->pathname, O_RDONLY);
 if(fifo->fd[0] == -1){
fifo_delete(&fifo);
  return NULL;
...

Thank you in advance for your help.

Answer 1

The value that you are passing is decimal 666, which corresponds to octal 01232 (01210 after applying ~umask).

You should be passing either 0666, or decimal 438.