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Asked: 2026-06-10T15:24:40+00:00

I am investigating ways to take a directory (folder) and derive some form of

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I am investigating ways to take a directory (folder) and derive some form of unique numerical identifier. I have investigated “string to hash” methods, however, the Pigeon Hole Principle means that one can never derive a truely unique number for every single string.

String to unique hash is no good.

I have recently been investigating other means of achieving my goal and thus have the following question to ask:

Directory time stamps – how ‘unique’ are they?
To what resolution are the time stamps reported by ‘stat’ as described here (second post)? if the resolution is small enough, is it possible for more than one folder to share the exact same time stamp on a Linux system?

If anyone has other methods/techniques they’d like to share, I’d be happy to listen 🙂

Edit 1 To clarify my use case in response to the answers posted so far: I am working on Android platforms, so the filesystem is not linked to any other (except of course for removeable media such as Micro SD cards).

I am inserting each path into a database but trying to avoid string comparisons when querying the table. The use of maps/hashmaps is not an option here. Yes, the path itself is unique, but ideally I need a numerical identifier that can be used to query the table as opposed to the path itself. The identifier must also be unique per path. I have experimented with std::collate but found there were many collides in the hashes (a dataset of 20, 000 paths yeilds approximatley 100 collides). What was even more surprising is that the hashes appeared to be largely different each time my application is run. I wonder if it’s seeded somehow?

Many thanks,
P

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1 Answer

  1. Editorial Team

    On any UNIX-based system, you can use the inode number as a unique identifier within that file system. Combining it with the device number will make it unique within the machine. If you wanted it to be globally unique, you could throw in the system’s primary MAC address.

    Keep in mind, however, that:

    1. The inode number will “follow” the directory if it is moved or renamed. It will change if the directory is deleted and replaced.

    2. The inode number will not be stable across systems, beyond one or two really special directories. (For instance, / is usually inode 2.)

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