bug#42440: closed (bug with rm)

[GNU bug Tracking System]

Your message dated Wed, 22 Jul 2020 00:05:34 -0600
with message-id <20200721234555688656350@bob.proulx.com>
and subject line Re: bug#42440: bug with rm
has caused the debbugs.gnu.org bug report #42440,
regarding bug with rm
to be marked as done.

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42440: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=42440
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--- Begin Message --- Subject: bug with rm Date: Mon, 20 Jul 2020 17:51:05 +0800

sometimes,rm can't delete the file.

but when using rm -rf + file .

the file can be deleted.

--- End Message ---

> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: bug#42440: bug with rm
>
>
>
>
> Date: 
>
> Wed, 22 Jul 2020 00:05:34 -0600
>
>
>
>
> tags 42440 + notabug
> thanks
>
> ���� wrote:
> > sometimes,rm can't delete the file.
> > but when using rm -rf + file .
> > the file can be deleted.
>
> This does not sound like a bug in the rm command.  Therefore I am
> tagging this as such.  If you have follow up information and this
> turns out to be an actual bug then we can reopen the bug report.
>
> Unfortunately there is not enough information in the report to know
> exactly the case that you are talking about.  For example I don't know
> if you are talking about a literal "+" in that line or not.  I will
> assume that you are since it is there.
>
> There are several FAQs listed for rm.  Any of these might be a
> problem.
>
>   
> https://www.gnu.org/software/coreutils/faq/coreutils-faq.html#How-do-I-remove-files-that-start-with-a-dash_003f
>   
> https://www.gnu.org/software/coreutils/faq/coreutils-faq.html#Why-doesn_0027t-rm-_002dr-_002a_002epattern-recurse-like-it-should_003f
>
> You might have experienced either of those problems.  Or a different
> problem.  We can't tell.
>
> > sometimes,rm can't delete the file.
>
> There are two main cases.  One is that if the file is not writable by
> the user then 'rm' will check for this and ask the user for
> confirmation.
>
>     rwp@angst:/tmp/junk$ touch file1
>     rwp@angst:/tmp/junk$ chmod a-w file1
>     rwp@angst:/tmp/junk$ rm file1
>     rm: remove write-protected regular empty file 'file1'? n
>     rwp@angst:/tmp/junk$ ls -l file1
>     -r--r--r-- 1 bob bob 0 Jul 21 23:52 file1
>
> The -f option will force it without prompting.
>
>     rwp@angst:/tmp/junk$ rm -f file1
>     rwp@angst:/tmp/junk$ ls -l file1
>     ls: cannot access 'file1': No such file or directory
>
> This is a courtesy confirmation.  Because the permissions on the file
> is not important when it comes to removing a directory entry.  A file
> is really just an entry in the directory containing it.  Removing a
> file simply removes the entry from the directory.  When the last link
> to the file reaches zero then the file system reclaims the storage.
> The file system is a "garbage collection" system using reference
> counting.
>
>     https://en.wikipedia.org/wiki/Garbage_collection_(computer_science)
>
> Therefore the only permission needed to remove a file is write
> permission to the directory containing it.
>
>     rwp@angst:/tmp/junk$ touch file2
>     rwp@angst:/tmp/junk$ ls -ld . file2
>     drwxrwxr-x 3 rwp rwp 100 Jul 21 23:56 ./
>     -rw-rw-r-- 1 rwp rwp   0 Jul 21 23:56 file2
>     rwp@angst:/tmp/junk$ chmod a-w .
>     rwp@angst:/tmp/junk$ ls -ld . file2
>     dr-xr-xr-x 3 rwp rwp 100 Jul 21 23:56 ./
>     -rw-rw-r-- 1 rwp rwp   0 Jul 21 23:56 file2
>
> This creates a file.  The file is writable.  But I have changed the
> directory containing it not to be writable.  This prevents the ability
> to remove the file.  Can't remove it because the directory is not wriable.
>
>     rwp@angst:/tmp/junk$ rm file2
>     rm: cannot remove 'file2': Permission denied
>     rwp@angst:/tmp/junk$ rm -f file2
>     rm: cannot remove 'file2': Permission denied
>     rwp@angst:/tmp/junk$ rm -rf file2
>     rm: cannot remove 'file2': Permission denied
>     rwp@angst:/tmp/junk$ ls -ld . file2
>     dr-xr-xr-x 3 rwp rwp 100 Jul 21 23:56 ./
>     -rw-rw-r-- 1 rwp rwp   0 Jul 21 23:56 file2
>
> In order to remove the file we must have write permission to the
> directory.  Adding write permission to the directory allows removing
> the file.
>
>     rwp@angst:/tmp/junk$ chmod ug+w .
>     rwp@angst:/tmp/junk$ rm file2
>     rwp@angst:/tmp/junk$ ls -ld file2
>     ls: cannot access 'file2': No such file or directory
>
> Expanding upon this problem is if there are many directories deep and
> the directories are not writable.
>
>     rwp@angst:/tmp/junk$ mkdir -p dir1 dir1/dir2 dir1/dir2/dir3
>     rwp@angst:/tmp/junk$ touch dir1/dir2/dir3/file3
>     rwp@angst:/tmp/junk$ chmod -R a-w dir1
>     rwp@angst:/tmp/junk$ find dir1 -ls
>      69649132      0 dr-xr-xr-x   3 rwp      rwp            60 Jul 22 00:00 dir1
>      69649133      0 dr-xr-xr-x   3 rwp      rwp            60 Jul 22 00:00 
> dir1/dir2
>      69649134      0 dr-xr-xr-x   2 rwp      rwp            60 Jul 22 00:00 
> dir1/dir2/dir3
>      69650655      0 -r--r--r--   1 rwp      rwp             0 Jul 22 00:00 
> dir1/dir2/dir3/file3
>
> That sets up the test case.  None of the directories are wriable.
> Therefore we cannot remove any of them.  The directory holding the
> entries must be writable.
>
>     rwp@angst:/tmp/junk$ rm -rf dir1
>     rm: cannot remove 'dir1/dir2/dir3/file3': Permission denied
>
> Even using 'rm -rf' does not work.  And should not work.  Because the
> directories are not writable.
>
> In order to remove these files the directories must be made writable.
>
>     rwp@angst:/tmp/junk$ chmod -R u+w dir1
>     rwp@angst:/tmp/junk$ rm -rf dir1
>     rwp@angst:/tmp/junk$ ls -ld dir1
>     ls: cannot access 'dir1': No such file or directory
>
> Hopefully this helps you understand how directory entries work, that
> the directory holding an entry (either file or another directory) must
> be writable.  How to add write permission.  How to remove a single
> file.  How to remove a directory tree.  Hopefully this helps! :-)
>
> Bob
>
>
> --- End Message ---