Why does hostname -h return 255

Question

"No news is good news", which, sticking with the normal convention should return 0. Why does

hostname -h 

return 255, especially when, 255 by convention, is meant to mean "Exit status out of range"

Answer 1

"hostname -h"

does not return 255 on my RHEL machine.

it does return error 4 which make sense

hostname -h
Usage: hostname [-v] {hostname|-F file}      set hostname (from file)
........
echo $?
4

If you take a look at hostname.c from net-utils you will clearly see that:

static void usage(void)
{
    fprintf(stderr, _("Usage: hostname [-v] {hostname|-F file}      set hostname (from file)\n"));
........
  exit(4); /* E_USAGE */
}

and reference to usage() in here in the same file:

........
    case '?':
    case 'h':
    default:
        usage();

    };

So i am not really sure why you are getting 255, on MAC version you might get "1", but i never seen "255".

EDIT you are right, i've just looked at fedora19 and hostname comes from hostname RPM and indeed for usage they do return 255:

void
usage(FILE *stream)
{
        fprintf(stream,
.....
 exit(-1);
}

;

So here I will try to explain your confusion.

Well, first doing exit(-1) there is a mistake by a programmer, at least for POSIX environment, since in such OS anything that not 0 in exit status considered FAILURE, but:

What about the exit() function found in the standard C library?

It’s manpage tells us that “the exit() function causes normal process termination and the value of status & 0377 is returned to the parent”.

Now, status & 0377?

What does that mean?

Well, 0377 is 377 in octal, which is 255 in decimal, or 0xFF in hexadecimal.

#include <stdlib.h>
void exit(int status);

So, if exit takes a signed argument, but returns a 0xFF masked one to its parent( which is shell), and “-1” is represented as all ones in two’s-complement, this only means that the value the shell is going to see and, thus, $? is going to store = 0xff Recall that 0xff is 255, and that’s pretty much it.

Even if programmer is aware that all user will get is 255 when he calls exit(-1), it is a poor habit to do that while programming in POSIX environment. The code will eventually reach someone that will misunderstand the meaning of the -1(255) argument and raise a question like you(OP) did.

Answer 2

In my Ubuntu, hostname -h return 255.

Using apt-get source hostname to get its source, diving into it, we can see that, if using -h options, hostname command will return -1, which is out of range:

void                                                                            
usage(FILE *stream)
{
....
    exit(-1);                                                                   
}

In main function, line 501:

case 'h':                                                               
            usage(stdout);                                                      
            break;

Answer 3

In later versions of hostname, version 3.15, it returns -1.

usage(FILE *stream)
{
  fprintf(stream,
    "Usage: hostname [-b] {hostname|-F file}         set host name (from file)\n"
...
...
  exit(-1);
}

This looks like a situation where the status is managed as a signed int, but is then at some point converted to an unsigned int.