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Inode and file Descriptor | An Introduction

Did you know that in Unix-like operating systems, files are represented by two data structures, inodes, and file descriptors?

Inodes can be described as data structures that store information about a file, like its size, permissions, and location on disk. Additionally, each file has a unique inode number, which identifies the file in the file system.

When a file is created, an inode is created to hold the file’s metadata. When a file is deleted, the associated inode is freed and can be reused for new files.

On the other hand, file descriptors are integers that refer to open files. When we open a file, the kernel assigns it a file descriptor. This file descriptor is a small non-negative integer. It can then be used to read from, write to, or close the file.

Furthermore, each process has its own set of file descriptors. By default, the first three file descriptors (0, 1, and 2) are reserved for standard input, standard output, and standard error.

The difference between the two is that an inode represents a file while a descriptor represents a ticket to access the file, with limited permission and time window. Inodes are stored on disk and are not deleted when a file is closed. File descriptors, on the other hand, are stored in memory and are deleted when a file is closed.

The relationship between inodes and descriptors can be seen below:

• Each file has a unique inode number.
• When a file is opened, the kernel assigns it a file descriptor.
• The file descriptor is used to access the file’s inode.
• The inode contains information about the file.

In addition to inodes and file descriptors, there are other data structures that help manage files. These include directory entries, indirect blocks, and extents.

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Conclusion

In summary, our Support Techs introduced us to Inode and file descriptors and the difference between them.