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Re: What is the difference between unlink and rm -f?

From: Eric Blake
Subject: Re: What is the difference between unlink and rm -f?
Date: Wed, 29 Jan 2020 07:22:37 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 1/29/20 3:45 AM, Peng Yu wrote:

It seems to me unlink and rm -f are the same if the goal is the delete
files. When are they different? Thanks.

On really old systems, it was possible to hard link directories together. This had to be done carefully to avoid creating file system loops, so generally it was limited to only the root user (in fact, before the mkdir(2) syscall was invented, directories were first implemented by mkdir(1) as a root program that manually manipulated raw directory entries with mknod in such a manner as to create proper directory hard links on your behalf: But if you had a situation with hard linked directories, and want to remove a directory entry no matter whether it is a file or a directory or even missing, while still getting at any errno message from the kernel: 'unlink' does the job perfectly, while 'rm' fails (it does not remove directories even if unlink could) and 'rm -f' squelches error messages (which doesn't help if your goal is to see the result of the syscall).

These days, all systems have mkdir(2) and rmdir(2) syscalls, and you can no longer use mknod to create directories nor create directory hard links. So you are right that the original distinction between the two programs is much less significant than it used to be.

And asking here shows that you didn't google very hard, as I quickly found this answer to the same question:

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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