Permissions

[Jeffrey Pyne]

One question that perplexed me when I first learned UNIX (actually Solaris),
was why, if I have a umask of 022, do new files I create get created with
644 permissions, not 755.  777 XOR 022 = 755, does it not?  It turns out
that the permissions of new files are determined by XORing your umask with
666, while the permissions of new directories are determined by XORing your
umask with 777.  So:

$ umask
022
$ touch foo
$ mkdir bar
$ ls -l
total 4096
-rw-r--r--    1 jpyne    jpyne           0 Dec 16 12:14 foo
drwxr-xr-x    2 jpyne    jpyne        4096 Dec 16 12:14 bar

I wonder, what was the historical reason for making the default permissions
of a new file 666 and a new directory 777?

~Jeff

On Sunday, December 15, 2002 8:41 PM, J.Francois wrote:

> A fully available file is like you have above:
> 
> 7 7 7  ==  rwx  rwx  rwx
>            111  111  111
> 
> a umask of 022, for example, means "take away access 
> permisions" like so:
> 
>   7 7 7  111 111 111
> - 0 2 2  000 010 010 <--- Here is your umask
> ======== ===========
>   7 5 5  111 101 101
>          rwx r-x r-x