what is inode in linux

In Linux and other Unix-like operating systems, an inode (index node) is a data structure on a filesystem that stores information about a file or a directory, excluding its name or its actual data. Each file or directory is assigned a unique inode number within a filesystem, and this inode number serves as an identifier for the file's metadata. Here's a breakdown of what an inode typically contains: 1. **Metadata**: Inodes store metadata about the file or directory, including: - File type (regular file, directory, symbolic link, etc.) - Permissions (read, write, execute for owner, group, and others) - Owner and group information (user ID and group ID) - Timestamps (creation time, last access time, last modification time) - Size of the file - Number of hard links pointing to the inode - Pointers to the disk blocks where the file data is stored 2. **Structure**: The inode itself does not contain the filename or the actual content of the file; rather, the filesystem maintains a separate mapping of filenames to their respective inode numbers. This allows for the same file to have multiple names (hard links). 3. **Identification**: Each inode is identified by a unique inode number, which can be viewed using commands like `ls -i` in the shell. For example, running `ls -i filename` will show you the inode number of that file. 4. **Limits**: The total number of inodes is fixed when the filesystem is created. If a filesystem runs out of inodes, you will not be able to create new files even if there is free space available. In summary, inodes are fundamental components of the filesystem in Linux, serving as records for all the essential properties of files and directories.