Re: Can not delete file with correct permissions
On Thu, May 06, 2021 at 06:04:31PM +0200, tomas@tuxteam.de wrote:
> OK. The problem is you have some directory where users are
> supposed to be able to create a file, but to only remove
> *their* files, but not other's.
>
> This is a well-known problem (/tmp also has that problem), and
> UNIX-like file systems have something for that. This is called
> the "sticky bit" [1].
>
> And lo and behold, *my* /var/mail has this sticky bit:
>
> | tomas@trotzki:~$ ls -al /var/mail
> | total 220
> | drwxrwsr-x 2 root mail 4096 Feb 25 15:30 .
> ^ Here it is
Incorrect. That's the setgid bit.
unicorn:~$ ls -ld /var/mail /tmp
drwxrwxrwt 16 root root 12288 May 6 12:39 /tmp/
drwxrwsr-x 2 root mail 4096 Jan 11 2018 /var/mail/
/tmp has the sticky bit, which is shown as a "t" in the lowest bit
position. /var/mail has the setgid bit, shown as an "s" in the group
execute bit's position.
MUAs are not expected to DELETE user inbox files. If you delete all of
the messages in your inbox, this should simply leave your inbox file
empty, not deleted.
There is no need for a user MUA to delete or rename inbox files in
system-wide /var/mail directories. There's an argument to be made that
it might want to *create* one if it doesn't already exist, but it can't,
so we simply ignore that. The inbox file will be created by the system
MTA when the first message is delivered to that user. At that point,
the user's MUA can read and write the existing file without problems.
(Insert arguments for user mailboxes to be in ~/Maildir/ instead.)
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