CODEWITHSUNDEEP
linuxshellcommand-linefilesystems
Jonovono
Jonovono

Reputation: 3425

Unique File Id?

I am making an application that will save information for certain files. I was wondering what the best way to keep track of files. I was thinking of using the absolute path for a file but that could change if the file is renamed. I found that if you run ls -i each file has an id beside it that is unique(?). Is that ok to use for a unique file id?

Upvotes: 2

Views: 6599

Answers (2)

nsfyn55
nsfyn55

Reputation: 15363

The inode is unique per device but, I would not recommend using it because imagine your box crashes and you move all the files to a new file system now all your files have new ids.

It really depends on your language of choice but almost all of them include a library for generating UUID's. While collisions are theoretically possible its a veritable non-issue. Generate the UUID prepend it to the front of your file and you are in business. As your implementation grows it will also allow you to create a HashTable index of your files for quick look ups later.

Upvotes: 4

dstromberg
dstromberg

Reputation: 7177

The question is, "unique across what?"

If you need something unique on a given machine at a given point in time, then yes, the inode number + device number is nearly always unique - these can be obtained from stat() or similar in C, os.stat() in python. However, if you delete a file and create another, the inode number may be reused. Also, two different hosts may have a completely different idea of what the device,inodeno pairs are.

If you need something to describe the file's content (so two files with the same content have the same id), you might look into one of the SHA or RIPEMD functions. This will be pretty unique - the odds of an accidental collision are astronomically low.

If you need some other form of uniqueness, please elaborate.

Upvotes: 1

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