simple umask question

danahata · 08-25-2003, 10:50 PM

Ok I do umask 0333, and then touch a file, and the file gets created with permissions of -r--r--r--, which is 0444. I thought that the file permissions are determined internally by ANDing the umask with another value, such as 0666 or 0777. But there is nothing that 0333 can be ANDed with to produce 0444. What am I missing here?

Dana

Skyline · 08-25-2003, 11:04 PM

A umask=0333 will give you

-r--r--r--

A umask=0444 will give you

--wx-wx-wx

You would typically set a umask value globally for all new files and directories created - locally you would typically use chmod

shellcode · 08-25-2003, 11:32 PM

$man umask | grep 666
666 & ~022 = 0644 = rw-r--r-- in the usual case where is mode is specified as 0666

666 - 022 = 644
you subtract the umask from 666 to get the permissions.

danahata · 08-26-2003, 09:27 AM

Ok, so the real answer is that the file permissions are determined this way -->

0666 AND (NOT umask)

Dana

kev82 · 08-26-2003, 09:47 AM

almost,

file_permision = requested_permision AND (NOT umask)

so with a umask of 022, trying to create a file with permission 777 will give it 755. requested permision is not necessarily 666 which you seemed to assume above.

danahata · 08-26-2003, 10:34 AM

Ok, I thought I had it- now I'm confused again. I guess I don't understand the concept of 'requested permission' as you described. What is it and how is it set? (Also why do you need it?) I guess I thought that the umask was a form of requested permissiion.

Dana

kev82 · 08-26-2003, 10:55 AM

sorry, what i said is unimportant, requested permission defaults to 0666 when creating files and 0777 when creating directories. so if you create a directory with umask 002 it will have permision 775

if you are programming when you create a file or directory you have to specify what permissions you want the file to initially have, this is what i mean by requested permission, however ive just checked and touch and mkdir dont let you choose this, they use 0666 and 0777 respectivly

danahata · 08-26-2003, 11:01 AM

Ok I've got it now.

For FILES:

file permission = 0666 AND (NOT umask)

I hope this helps others!

Dan

Skyline · 08-26-2003, 11:04 AM

You can change the default umask value in /etc/profile.