Hi,

I'm reading "Beginning Linux Programming (4th Edition)", published in 2007.

In chapter 3 - "Working with files", page 94, they said:

"When you delete a file all that happens is that the directory entry for the file is removed and the number of links to the file goes down by one. The data for the file is possibly still available through other links to the same file. When the number of links to a file (the number after the permissions in ls -l) reaches zero, the inode and the data blocks it references are then no longer in use and are marked as free."

I still don't understand this even after searching Google for more information. So when we delete a file, its data is still available if there is something's linked to it?

Anyone could explain more for me, or give me a example please.

Thank you so much!

Regards,
Hung

Try this link for more info:

http://www.linux.com/archive/feature/58142

I'm reading this one now.

I figure it's something like this ...

A file is a base inode plus none or more indirectly linked inodes plus none or more data blocks as explained here. Its name(s) are contained in directory entries which point to the base inode; the base inode has a count of the number of such links. When a directory entry is removed the link count is decremented and the kernel checks the new number of links. If it is zero the kernel checks if any processes have the file open (this information is in kernel memory) and if it is zero the kernel deletes the file otherwise it waits for the process(es) to close the file and each time that happens it checks again to see if any processes have the file open (described here). Presumably actually deleting the file means marking all its inodes as free.

What happens if there is a power failure while a file has no directory entries but is held open by one or more processes? There is no opportunity to delete it (as described above) but it is not accessible either. Presumably that is why it is good practice to run fsck after a power failure so this can be rectified.

There is no such thing as base inode or indirectly linked inodes. The file can have many names and many blocks associated with it but it always has exactly one inode. For regular files the inode contains file permissions, number of hard links (this is the same as the number of names of the file) etc.

1 members found this post helpful.

Thank you for the correction