14.4. I-nodes

A file system’s i-node table contains one i-node (short for index node) for each file residing in the file system. I-nodes are identified numerically by their sequential location in the i-node table. The i-node number (or simply i-number) of a file is the first field displayed by the ls -li command. The information maintained in an i-node includes the following:

• File type (e.g., regular file, directory, symbolic link, character device).

• Owner (also referred to as the user ID or UID) for the file.

• Group (also referred to as the group ID or GID) for the file.

• Access permissions for three categories of user: owner (sometimes referred to as user), group, and other (the rest of the world). Section 15.4 provides further details.

• Three timestamps: time of last access to the file (shown by ls -lu), time of last modification of the file (the default time shown by ls -l), and time of last status change (last change to i-node information, shown by ls -lc). As on other UNIX implementations, it is notable that most Linux file systems don’t record the creation time of a file.

• Number of hard links to the file.

• Size of the file in bytes.

• Number of blocks actually allocated to the file, measured in units of 512-byte blocks. There may not be a simple correspondence between this number and the size of the file in bytes, since a file can contain holes (Section 4.7), and thus require fewer allocated blocks than would be expected according to its nominal size in bytes.

• Pointers to the data blocks of the file.