should my program lock /etc/.pwd.lock when reading /etc/passwd?

fpemud · 10-08-2014, 06:09 PM

I'm writing some program that operates /etc/{passwd,group,shadow,gshadow}.

I learned that any program should lock /etc/.pwd.lock by calling lckpwdf() before writing the above files so that write collisions can be avoided.

I guess reading operation also needs this lock so that program won't read out inconsistent data.

But I found I can't do the lock when reading /etc/passwd as non-root, because /etc/.pwd.lock is owned by root:root and has mode 0600.

Am I wrong? Doesn't reading need this lock?

linosaurusroot · 10-09-2014, 01:22 PM

Reading doesn't need the lock because the file should be replaced rather than modified.

Are you sure you should be reading these rather than using the likes of getpwent() ?