Andrey Borodin <x4mmm(at)yandex-team(dot)ru> writes:
> Is it safe to use file modification time to track that file were changes
> since previous backup?
I'd say no:
1. You don't know the granularity of the filesystem's timestamps, at least
not without making unportable assumptions.
2. There's no guarantee that the system clock can't be set backwards.
3. It's not uncommon for filesystems to have optimizations whereby they
skip or delay some updates of file mtimes. (I think this is usually
optional, but you couldn't know whether it's turned on.)
#2 is probably the worst of these problems.
regards, tom lane