What UNIX called an inode is unfortunately not what Linux now calls an inode. That thing might have better names, but we are stuck with it.

I don't know if it is useful to say "Linux inode" because that can refer to both what "ext4" calls an inode and what the Linux kernel refers to as a "virtual inode".

What POSIX called a "file serial number" (and goes in the `d_ino` field) is also not what Linux calls an inode. I sometimes think this is okay to refer to as a "POSIX inode" because POSIX doesn't otherwise use the term, and up until SUS6 the POSIX file serial number was compatible with a UNIX inode.

However I'm not trying to nit: Trying to develop a simplified mental model is essential to determining what to do (and what to sync!). From an application point of view, knowing that a symbolic link has a name (and contents) and lives in a directory, can help guide us.

How so? Here's a v6 on-disk inode: https://github.com/hephaex/unix-v6/blob/master/ino.h

and here's an ext4 on-disk inode: http://lxr.free-electrons.com/source/fs/ext4/ext4.h#L704

The latter is considerably larger, to be sure, but still contains all of the fields from the former (many of them with the same name!).

UNIX called them "inode" and "permanent inode"; Linux calls them "in-memory inode" and "on-disk inode". The BSDs use "vnode" and "inode".