[NTLUG:Discuss] MAJOR mess

[Steve Baker]

R P Herrold wrote:
> 
> On Sat, 27 Oct 2001, Jim Wildman wrote:
> 
> > Oh sure you're _supposed_ to....but real geeks edit passwd with
> > echo "newuser::..." >> /etc/passwd.  They don't even bother with vi!

I did do something like that once. (I used:

   # cat <<HERE >>/etc/passwd
   ? newuser::...
   ? HERE

It was on a Z8000-based machine from ONYX computing that didn't have a
working 'vi'. Faced with the alternatives, I chose 'cat' rather than
using 'ed'.  There are times when even a real geek knows when to back
down!

> ... ohhh ... we geeks could accidentally make that root userid
> deletion too -- my fingers might slip and type:
> 
>   grep -v ^root: /etc/passwd > /etc/pwtemp ; mv /etc/pwtemp \
>         /etc/passwd
> 
> and I'd be in the same mess ... (more ...)

You'd probably have bad permission bits on /etc/passwd too.
 
> MUCH worse would be:
> 
>   grep -v ^root: /etc/passwd > /etc/passwd
> 
> Anyone want to comment why <grin>?

That's *too* easy!

Because that completely erases *all* the passwords.

When you first hit return, the shell sees that you want to create the file
/etc/password and hence opens it for writing.  That creates a zero length
file. Then the shell starts grep which is now grepping an empty file.

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