[NTLUG:Discuss] umask (was: Permissions)

[Steve Baker]

Hrothgar wrote:
> 
> On Fri, 3 Sep 1999 Kyle_Davenport at compusa.com wrote:
> 
> :</snip>
> :and set joe's umask:
> :umask 002
> :</snip>
> :
> 
> could someone tell me what umask is?  the bash man page doesn't tell me
> jack-squat.  thanks

It determines what permissions you wish to deny when you create a file.

Hence if you did this:

% umask 777 ; touch t1
% umask 007 ; touch t2
% umask 077 touch t3
% ls -l t?
----------   1 steve    users           0 Sep  3 19:36 t1
-rw-rw----   1 steve    users           0 Sep  3 19:36 t2
-rw-------   1 steve    users           0 Sep  3 19:36 t3

You can see that with a umask of 777, files come out with NO permissions
granted at all!

With 007, you prohibited the world from messing with your files.

With 077, you prohibited the world *and* members of your group from
accessing files that you create.

umask with no parameters displays your current umask.

At work, I usually set mine to:

   umask 026

...which doesn't prevent any of my permissions from getting through, it
allows members of my group to read and execute my files - but not write
to them - and it allows anyone to execute programs/scripts I write.

At home, I use:

   umask 0

...just because wide-open permissions work fine for me at home.

Your choices may well be different.

Typically, you'd only use umask in your login script - but you
could imagine other situations where it would matter.

Note that umask can only deny additional privilages - it can't
add them.

Hence, when I did:

   umask 007 ; touch t2

...it didn't give the file execute-by-owner or execute-by-group
privilages
because 'touch' didn't want to grant them - even though a umask of 007
*allows* it to grant that permission.

-- 
Steve Baker                  http://web2.airmail.net/sjbaker1
sjbaker1 at airmail.net (home)  http://www.woodsoup.org/~sbaker
sjbaker at hti.com      (work)