The Devils 0666 File Creation Permission

Author profile picture

@taha-alami-idrissiTaha ALAMI IDRISSI

As far as I can tell, this is hard-coded into standard utilities. I straced both a touch creating a new file and a mkdir creating a new directory.

The touch trace produced this:
open("newfile", O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 0666) = 3
while the mkdir trace produced this:
mkdir("newdir", 0777)
Short of coding the file/directory creation process in C, I don't see a way of modifying the default permissions. It seems to me, though, that not making files executable by default makes sense: you don't want any random text to be accidentally misconstrued as shell commands.
Update
To give you an example of how the permission bits are hard-coded into the standard utilities. Here are some relevant lines from two files in the coreutils package that contains the source code for both
touch(1)
 and
mkdir(1)
, among others:
mkdir.c:
if (specified_mode)
   {   
     struct mode_change *change = mode_compile (specified_mode);
     if (!change)
       error (EXIT_FAILURE, 0, _("invalid mode %s"),
              quote (specified_mode));
     options.mode = mode_adjust (
                      S_IRWXUGO, true, 
                      umask_value, change,
                      &options.mode_bits
                    );
     free (change);
   }   
  else
    options.mode = S_IRWXUGO & ~umask_value;
}   
In other words, if the mode is not specified, set it to S_IRWXUGO (read:
0777
) modified by the umask_value.
touch.c is even clearer:
int default_permissions = 
  S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
That is, give read and write permissions to everyone (read:
0666
), which will be modified by the process umask on file creation, of course.
You may be able to get around this programmatically only: i.e. while creating files from within either a C program, where you make the system calls directly or from within a language that allows you to make a low-level syscall (see for example Perl's sysopen under perldoc -f sysopen).


Tags

The Noonification banner

Subscribe to get your daily round-up of top tech stories!