Re: [coreutils] RFC for adding file creation mode feature into touch utility.

[Bob Proulx]

Rakib Mullick wrote:
> Jim Meyering wrote:
> > Why do you want an option for this when you can already use touch
> > to create a file with selected permissions via your umask?
> 
> I think umask change the the file creation mask system wide. I might
> not want it for every file I create.

No.  The umask only affects the current process.  It doesn't affect
other processes system wide.  It will affect files created by the
current process, but that is the point of it.

> > If you say that you require an execute bit or some special bit to
> > be set, please explain why.  I do not see how having such bits set
> > on an empty file would be useful.  If you're about to add content,
> 
> No. It's not just about setting an execute bit, say I might have
> create a file with 'sudo touch filename', in that case I just can see
> the file by doing 'cat filename' or 'vim filename'.

In which case the file is zero sized.  Emitting the file with 'cat'
would read a zero sized file.  But you wouldn't want to edit the file
with 'editor filename'.  Since you specifically created it as a root
owned file then the user would not have permissions to edit the file.
And you wouldn't want to 'sudo editor filename' either because of the
security implications.  You /may/ want to use 'sudoedit'.

> So, again I need to do, 'sudo chmod xxx filename' to make it
> available to its user. So, it can be summed up as:

Please say exactly what mode bits you want to set.  That was the
question asked in the last email.  Please don't say mode xxx but
instead say exactly what mode bits you are talking about.

Because otherwise we have to imagine and guess.  I can only guess that
you mean to make it unavailable, right?

  $ sudo touch /tmp/afile
  $ ls -l /tmp/afile
  -rw-r--r-- 1 root root 0 Jan  9 11:48 /tmp/afile

If you wanted to block it then you should need to chmod it.

  $ sudo chmod go-rwx /tmp/afile
  $ ls -l /tmp/afile
  -rw------- 1 root root 0 Jan  9 11:48 /tmp/afile

> (Assume, to create a file under /usr/src/work)
>              sudo touch /usr/src/work/filename (to create a file)
>              sudo chmod xxx /usr/src/work/filename (to give a user proper 
> permission)

Please say exactly what mode bits you want to set.

Because with the above touch you would have a root owned file.  The
only way you could give a user permission to write to the file would
be to open it up for global writing by any user.

  $ sudo chmod ugo=rw /tmp/afile
  $ ls -l /tmp/afile
  -rw-rw-rw- 1 root root 0 Jan  9 11:48 /tmp/afile

That is bad.  You do not want to do this.

> After adding this feature we can do this:
>             sudo touch --mode xxx /usr/src/work/filename
> thats it.

As I read your message you are saying you want to do:

  sudo touch --mode ugo=rw /usr/src/work/filename

Instead of doing:

  sudo touch /usr/src/work/filename
  sudo chmod ugo=rw /usr/src/work/filename

Just wishing to reduce two commands down to one command is not a good
reason for doing this.

Secondly you don't want to make files writable by other just to share
them.  That is bad.

If you want to provide for a group of users to be able to share access
to a file then you should use group permissions.  Create a work group
for use by the group.  Make the directory owned and writable by the
group.  Then when new files are created it will be owned by the group.
There is no need to use sudo.  Just operate as a normal user.  For
each user that is to have access to this group add that user to the
group.

This is a very short summary of the process.  Search the web for User
Private Group and read about how Unix file group permissions enable
this behavior natively.  I believe this is the concept that you should
be using.

Bob