passwd access method?

[Mark Wolfe]

    As a part of beefing up security on the machines I administer, I'm working
on implementing password aging. In order to simplify the process, I wrote a 
program that runs at login time and reports the time left before the users
password expires. If there is not an aging field on the entry, I generate one
and append it to the password field. 

    My question is this:
    Is there a proper way to access the passwd file to insure file inegrity and
security? I use the lockf call to reduce the chance of simultaneous access doing
some unknown damage to the file. Is this sufficient, or are there other checks
I should be making to insure multiple accesses leave the file in a good state?

    I guess I'm trying to find out if there is some standard (even defacto
standard) method of accessing the password file, or does everyone that does 
this invent their own method.

Mark

markw at hpbs1529