What information does an inode store?

The inode stores metadata about a file or directory in a filesystem. It does not contain the actual file data.

Key information stored in an inode:

• File type (regular file, directory, symbolic link, etc.)
• Access rights (owner, group, others; read, write, execute permissions)
• Number of hard links to this inode
• Owner user ID (UID)
• Owner group ID (GID)
• File size in bytes
• Timestamps:
  • Last access time (atime)
  • Last modification time (mtime)
  • Last status change time (ctime)
• Disk block numbers where file data is stored
• Data block size

Example structure (conditional):

// Conditional representation of inode structure
struct inode {
    // File metadata
    unsigned int    i_mode;      // File type and permissions
    unsigned int    i_uid;       // Owner UID
    unsigned int    i_gid;       // Owner GID
    unsigned int    i_nlink;     // Number of hard links
    __time_t        i_atime;     // Last access time
    __time_t        i_mtime;     // Last modification time
    __time_t        i_ctime;     // Creation/modification time
    unsigned long   i_size;      // File size
    unsigned long   i_blocks;    // Number of blocks occupied by the file
    unsigned int    i_blksize;   // Filesystem block size
    // Data block addresses (direct, indirect, depending on FS)
    unsigned int    i_block[N_BLOCKS]; 
    // + additional FS-specific information
};

Table with access rights examples in octal system:

Octal value	Description
777	All rights for owner, group, others
755	rwx for owner, r-x for group and others
644	rw- for owner, r-- for group and others