HighMem

It's so easy yet it took me quite a while to 'google' it out.

The problem: Being root you would like to resume another user's screen session. Let the user be A.

You 'become' him by

su A -

Then you would like to

screen -r

but unfortunately this gives you an error:

Cannot open your terminal '/dev/pts/0' - please check.

or something similar. The simple cause is that user A does not have the right to write into your (root's) terminal. This can be fixed by chmod'ing the above displayed file. For example:

chmod a+rwx /dev/pts/0

Do it as root and be aware that this is a severe security risk!