File table in Ubuntu OS

Question

Does linux/Ubuntu OS creates a table, which keeps the entry of every file with its absolute address that is stored on the hard drive?

Just curious to know, because I am planning to make a file searcher program.

I know there are terminal commands like find etc, but as I will program in C I was thinking if there any such thing Ubuntu OS does, if so, how can I access that table?

Update:

As some people mentioned there is no such thing, then If I want to make a file searcher program, I would have to search each and every folder of every directory, starting program root directory. The resultant program will be very sluggish and will perform poorly! So is there a better way? Or my way is good!

Answer 1

The "thing" you describe is commonly called a file system and as you may know there's a choice of file systems available for Linux: ext3, ext4, btrfs, Reiser, xfs, jffs, and others.

The table you describe would probably map quite well onto the inode-directory combo.

From my point of view, the entire management of where files are physically located on the harddisk is none of the user's business, it's strictly the operating system's domain and not something to mess with unless you have an excellent excuse (like you're writing a data recovery program) and very deep knowledge of the file system(s) involved. Moreover, in most cases a file's storage will not be contiguous, but spread over several locations on the disk (fragments).

But the more important question here is probably: what exactly do you hope to achieve by finding files this way?

EDIT: based on OP's comment I think there may be a serious misunderstanding here - I can't see the link between absolute file addresses and a file searcher, but that may be due to a fundamental difference between our respective understanding of "absolute address" in the context of a file system.

If you just want to look at all files in the file system you can either

1. perform a recursive directory read or
2. use the database prepared by updatedb as suggested by SmartGuyz

As you want to look into the files anyways - and that's where almost all runtime will be spent on - I can't think of any advantage 2) would have over 1) and 2) has the disadvantage to have an external dependency, in casu the file prepared by updatedb must exist and be very fresh.

An SO question speaking about more advanced ways of traversing directories than good old opendir/readdir/closedir : Efficiently Traverse Directory Tree with opendir(), readdir() and closedir()

EDIT2 based on OP's question addendum: yes, traversing directories takes time, but that's life. Consider the next best thing, ie locate and friends. It depends on a "database" that will be updated regularly (typically once daily), so all files that were added or renamed after the last scheduled update will not be found, and files that were removed after the last scheduled update will be mentioned in the database although they don't exist anymore. Assuming locate is even installed on the target machine, something you can't be sure of.

As with most things in programming, it never hurts to look at previous solutions to the same problem, so may I suggest you read the documentation of GNU findutils?

Answer 2

No, there is no a single table of block addresses of files, you need to go deeper.

First of all, the file layout depends on the filesystem type (e.g. ext2, ext3, btrfs. reisersf, jfs, xfs, etc). This is abstracted by the Linux kernel, which provides drivers for access to files on a lot of filesystems and a specific partition with its filesystem is abstracted under the single Virtual File System (the single file-directory tree, which contains other devices as its subtrees).

So, basically no, you need to use the kernel abstract interfaces (readdir(), /proc/mounts and so on) in order to search for files or roll your own userspace drivers (e.g. through FUSE) to examine raw block devices (/dev/sda1 etc) if you really need to examine low-level details (this requires a lot of understanding of the kernel/filesystems internals and is highly error-prone).

Answer 3

updatedb -l 0 -o db_file -U source_directory

This will create a database with files, I hope this will help you.

Answer 4

No. The file system is actually structured with directories, each directory containing files and directories.

Within Linux, all of this is managed into the kernel with inodes.

Answer 5

YES.

Conceptually, it does create a table of every file's location on the disc**. There are a lot of details which muddy this picture slightly.

However, you should usually not care. You don't want to work at that level, nor should you. There are many filesystems in Linux which all do it in a slightly (or even significantly) different way.

** Not actually physical location. A hard drive may map the logical blocks to physical blocks in some way determine by its firmware.