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call the unlink function to remove the specified file


unlink FILE

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(How) does deleting open files on Linux and a FAT file system work?

You are correct in your assumption that while all directory entries are deleted immediately after calling unlink(), the actual blocks that physically make up the file are only cleared on disk when nothing is using the inode anymore. (I say "directory entries" because in vfat, a file can actually have several of those, because of how vfat's long file name support is implemented.)

In this context, by inode, I mean the structure in memory that the Linux kernel uses for handling files. It is used even when the filesystem is not "inode based". In the case of vfat, the inode is simply backed by some blocks on disk.

Taking a look at the Linux kernel source code, we see that vfat_unlink, which implements the unlink() system call for vfat, does roughly the following (extremely simplified for illustration):

static int vfat_unlink(struct inode *dir, struct dentry *dentry)
        fat_remove_entries(dir, &sinfo);

So what happens is:

  1. fat_remove_entries simply removes the entry for the file in its directory.
  2. clear_nlink sets the link count for the inode to 0, which means that no file (i.e. no directory entry) points to this inode anymore.

Note that at this point, neither the inode nor its physical representation are touched in any way (except for the decreased link count), so it still happily exists in memory and on disk, as if nothing happened!

(By the way, it's also interesting to note that vfat_unlink always sets the link count to 0 instead of just decrementing it using drop_link. This should tip you off that FAT filesystems do not support hard links! And is further indication that FAT itself does not know of any separate inode concept.)

Now let's take a look at what happens when the inode is evicted. evict_inode is called when we do not want the inode in memory anymore. At its earliest, this can of course only happen when no process holds any open file descriptor to that inode anymore (but may in theory also happen at a later time). The FAT implementation for evict_inode looks (again, simplified) like this:

static void fat_evict_inode(struct inode *inode)
        truncate_inode_pages(&inode->i_data, 0);
        if (!inode->i_nlink) {
                inode->i_size = 0;
                fat_truncate_blocks(inode, 0);

The magic happens exactly within the if-clause: if the inode's link count was 0, it means that no directory entry is actually pointing to it. So we set its size to 0 and actually truncate it down to 0 bytes, which actually deletes it from disk by clearing up the blocks it was made of.

So, the corruption you are experiencing in your experiments is easily explained: Just as you suspected, the directory entry has already been removed (by vfat_unlink), but because the inode wasn't evicted yet, the actual blocks were still untouched, and were still marked in the FAT (an acronym for File Allocation Table) as used. fsck.vfat however detects that there is no directory entry which points to those blocks anymore, complains, and repairs it.

By the way, CHKDSK would not just clear those blocks by marking them as free, but create new files in the root directory pointing to the first block in each chain, with names like FILE0001.CHK.


Unlinking an open file then crashing

After a system crash there will be one of two conditions: either the journal will be recovered or fsck will be run. Did you seen Clearing orphaned inode XXXXX messages it's printing on boot? This is exactly your case: an inode that is not referenced from anywhere in the filesystem.


Call the unlink function to remove the specified FILE.


display this help and exit


output version information and exit


Copyright © 2012 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <>.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

reporting bugs

Report unlink bugs to bug-coreutils[:at:]gnu[:dot:]org
GNU coreutils home page: <>
General help using GNU software: <>
Report unlink translation bugs to <>

see also


The full documentation for unlink is maintained as a Texinfo manual. If the info and unlink programs are properly installed at your site, the command

info coreutils 'unlink invocation'

should give you access to the complete manual.


Written by Michael Stone.

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