Re: core(5)

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

On Sat, 6 Jun 2020 at 20:32, Jakub Wilk <jwilk@jwilk.net> wrote:
>
> * Jonny Grant <jg@jguk.org>, 2020-06-06, 16:45:
> >>>3) Could i ask to clarify my understanding. For this "The binary
> >>>being executed by the process does not have read permission enabled."
> >>>-- is this when the binary permissions are changed after it starts
> >>>running?
> >>No, AFAICS the permission check is done when the process starts.
> >How can the process start if the binary file doesn't have read
> >permissions enabled?
>
> It's a bit weird, but the kernel doesn't mind:
>
>    $ cp /bin/ls .
>    $ chmod a-r ls
>    $ ./ls -l ls
>    --wx--x--x 1 jwilk jwilk 138856 Jun  6 20:22 ls

And from core(5):

       There are various circumstances in which a core dump file  is  not
       produced:
       ...
       *  The binary being executed by the process  does  not  have  read
          permission enabled.

So, the binary can be executed, but not read, and will not do a core
dump (since that might be readable).

Thanks,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/