Problems with screen on Windows 10 Preview system
Corinna Vinschen
corinna-cygwin@cygwin.com
Sat May 2 16:47:00 GMT 2015
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:
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.
HTH,
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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