Bug#841935: pbuilder: incorrect permissions on /dev/ptmx breaks openpty()

[James Clarke]

> On 6 Nov 2016, at 20:34, Yuriy M. Kaminskiy <yumkam at gmail.com> wrote:
> 
> Andreas Henriksson <andreas at fatal.se> writes:
> 
>> It seems /dev/ptmx has incorrect permissions in a pbuilder chroot:
>> 
>> # ls -l /dev/ptmx
>> lrwxrwxrwx 1 root root 8 Oct  4 06:43 /dev/ptmx -> pts/ptmx
>> # ls -l /dev/pts/ptmx
>> c--------- 1 root root 5, 2 Oct 24 14:46 /dev/pts/ptmx
>> 
>> Please compare to what's stated in
>> https://www.kernel.org/doc/Documentation/filesystems/devpts.txt
>> 
>> For comparison this is from my regular system:
>> $ ls -l /dev/ptmx /dev/pts/ptmx
>> crw-rw-rw- 1 root tty  5, 2 okt 24 17:03 /dev/ptmx
>> c--------- 1 root root 5, 2 okt 11 12:35 /dev/pts/ptmx
>> 
>> I've hacked up my pbuilder installation and confirmed that appending
>> ",ptmxmode=0666" to the /dev/pts mount flags fixes the issue.
> 
> IIRC, it would also need `,newinstance` option by then (otherwise
> it will clobber "host system" devpts options).

newinstance seems to be a world of pain, as then it can’t access the TTY
for std{in,out,err}. I tried many months ago and couldn’t get it to work,
but would love to be proved wrong.

James