Re: Emacs cannot write file in a Virtual Box shared folder

[Robert Pluim]

>>>>> On Mon, 21 Oct 2019 20:22:04 +1100, Bernardo <bernardo.bacic@pobox.com> 
>>>>> said:

    Bernardo> Greetings,

    Bernardo> Running GNU Emacs in Debian (9.11) VM guest under VirtualBox host 
(6.0.14) running on Windows 10 box.
    Bernardo> (hope all this makes sense)

    Bernardo> Am having problems editing files located in a Virtual Box shared
    Bernardo> directory. The directory is owned by root but members of 'vboxsf'
    Bernardo> group have read/write/execute rights.  Emacs user is a member of
    Bernardo> 'vboxsf' group.

    Bernardo>  $ groups
    Bernardo>   some_user cdrom sudo audio <snip> bluetooth vboxsf

    Bernardo> The (old) version of Emacs that comes with Debian reads/writes 
files ok;
    Bernardo>   GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.11) of 
2017-09-12 on hullmann, modified by Debian

    Bernardo> The version of Emacs that's built from Git repos cannot write
    Bernardo> file. Also by default it opens the file in read-only mode.
    Bernardo>   GNU Emacs 27.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 
3.22.11) of 2019-10-21

    Bernardo> Debugger entered--Lisp error: (file-error "Unlocking file" 
"Operation not permitted" "/media/sf_Home/zz_stuff")
    Bernardo>   write-region(nil nil "/media/sf_Home/zz_stuff" nil t 
"/media/sf_Home/zz_stuff")
    Bernardo>   basic-save-buffer-2()
    Bernardo>   basic-save-buffer-1()
    Bernardo>   basic-save-buffer(t)
    Bernardo>   save-buffer(1)
    Bernardo>   funcall-interactively(save-buffer 1)
    Bernardo>   call-interactively(save-buffer nil nil)
    Bernardo>   command-execute(save-buffer)

Looks like emacs is trying to create/delete a lockfile, and
failing. Does /media/sf_Home support symlinks?

You can work around this temporarily by customizing 'create-lockfiles'
to nil, but then emacs won't detect if youʼre editing the same file
from a different emacs session.

Robert