Problems with screen on Windows 10 Preview system

Stephen John Smoogen
Sat May 2 18:57:00 GMT 2015

On 2 May 2015 at 07:47, Corinna Vinschen <> wrote:
> On May  1 17:32, Stephen John Smoogen wrote:
>> I downloaded and installed a copy of Windows 10 on a spare system to
>> see how Cygwin works. Most of the applications worked similarly to
>> what I was testing on my Windows 7 system. However I have run into a
>> problem with the screen command.
>> The first time I run screen the command gives me a standard help
>> screen and data. If I type exit to get back to mintty and then
>> type screen again.. I get:
>> Directory '/tmp/uscreens' must have mode 777.
>> Which after going through the faq and old mailing list was
>> something that occurred on FAT partitions. So I went to check the
>> install and the file format is NTFS. I then looked at /tmp and
>> got
>> drwx---rwt+ 1 smoog smoog 0 May 1 16:01 uscreens
> You're using a "Microsoft Account", one of those for twhich the primary
> group SID is set to the same SID as your user account has.  So
> uid==gid==the exact same SID.  The group "smoog" is NOT a group called
> "smoog", it's your user account.  This leads to a chicken-egg problem:

Oooooh that explains a lot. I was figuring there was an issue with my
account but I wasn't sure if this was a new one due to Windows 10
preview, or something I didn't know about Windows account systems.
[Time to get a book on deep Windows internals and administration.]

> Either Cygwin sets the group permissions in the POSIX permission
> attributes to the same value as the user permissions, e.g.
>   rwxrwxr-x
> then security-sensitive POSIX applications will complain that the
> permissions are too wide-open.
> Or, Cygwin sets the group permissions to 0, e.g.
>   rwx---r-x
> Then, apparently, screen complains.
> There would be a third way, which is, to spill the "other" permissions
> into the group permissions, in my example:
>   rwxr-xr-x
> That should work, but needs YA patch to Cygwin and needs some testing.
> Bad timing right now (vaca).
> Workaround:  Set the primary group to the affected files explicitely to
> an existing group which is in your user token.  That would typically be
> the group "users", e.g.
>   chgrp users /tmp/uscreens
> should work, and then you can chmod it and screen should stop
> complaining.

Thank you for answering while you are on vacation. I am going to see
if a /etc/passwd and /etc/group entry to better fix that long term.

> HTH,
> Corinna
> --
> Corinna Vinschen                  Please, send mails regarding Cygwin to
> Cygwin Maintainer                 cygwin AT cygwin DOT com
> Red Hat

Stephen J Smoogen.

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