Re: New!!!: Base-passwd 2.0
I've just reviewed the code for chsh, passwd, vipw and rpc.yppasswd and they
all use the /etc/ptmp locking mechanism. Although it's slightly different
from how I remember it for SunOS.
> 1) open(2) /etc/ptmp (with O_CREAT|O_EXCL)
> (if that fails, wait and try again)
> 2) read in /etc/passwd and write changed passwd file to /etc/ptmp
> (in this way /etc/passwd is maintained intact for others to use
> while you make your changes)
> 3) rename(2) /etc/ptmp to /etc/passwd
> (rename is a guaranteed atomic action)
>
> The same is tru for /etc/group except that /etc/gtmp is used.
The only thing that changes is that in step 3 they do a hard link
from /etc/passwd to /etc/ptmp and then unlink /etc/ptmp. (Effectively
a rename. I suspect that a rename isn't guaranteed atomic in linux?)
Anyone can confirm the above by checking out the nis and loginutils
source packages.
I would suggest using this same locking mechanism and even making sure
all debian utils that deal with /etc/passwd uses this same mechanism.
At my old IT job, not all the in house UNIX utils used use this, and
once a month (sometimes even once a week) /etc/passwd would be corrupted
(at the time /etc/passwd was over 6000 entries!). The symptomes were
that usually about half of all users couldn't login. Eek! Oh well.
I hope this helps!
Behan
--
Behan Webster mailto:behanw@verisim.com
(613) 224-7547 http://www.verisim.com/
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